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Good sleep, good learning, good life

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Dr Piotr Wozniak, May 2012 (updated Oct 21, 2017)

I have for years been interested in sleep research due to my professional involvement in memory and learning. This article attempts to produce a synthesis of what is known about sleep with a view to practical applications, esp. in people who need top-quality sleep for their learning or creative achievements. Neurophysiology of sleep is an explosively growing branch of science. Many theories that are currently contested will soon be forgotten as a result of new findings. Consequently, this text is likely to grow old very quickly (compare the old version from the year 2000 here). Still, some basic truths about sleep are well-established, and practical conclusions can be drawn with the benefit to human creativity and intellectual accomplishment. In this text, I provide some links to research papers and popular-scientific articles that advocate disparate and contradictory theories. Please consult other sources to be certain you do not to get a one-sided view! This article includes some indications on how to use free running sleep in the treatment of insomnia, advanced and delayed phase shift syndromes, and some other sleep disorders. If your own experience can contribute to the ideas presented herein, I will gladly hear from you (esp. in the context of learning and creativity).

1 Foreword

1.1 Notes

2 Importance of sleep

2.1 Why understanding sleep is important?

2.2 Why do we sleep?

2.2.1 Disk and RAM metaphor
2.3 Bad sleep kills and costs billions

2.4 If you do not sleep, you die!

2.4.1 Brain's garbage collection
2.4.2 Sleep protection
2.4.3 Anabolic sleep
2.4.4 Why do we die without sleep?

2.5 Two components of sleep

2.5.1 Circadian component
2.5.2 Homeostatic component
2.5.3 Clock and Hourglass metaphor

2.5.4 The fundamental theorem of good sleep

2.5.4.1 When good sleep might not come?

3 Formula for good sleep

3.1 Free running sleep

3.2 Should we free run our sleep?

3.2.1 Argument 1: Phase shifts
3.2.2 Argument 2: Excessive sleeping
3.2.3 Free running sleep is stressless

3.3 Free running sleep algorithm

3.3.1 Cardinal mistakes in free running sleep
3.3.2 Sleep logging tips

3.4 Optimizing the timing of brainwork

3.4.1 Circadian graph and brainwork
3.4.2 Best brainwork time
3.4.3 Balanced 24 hour cycle
3.5 Sleeping against your natural rhythm

3.6 Kill the alarm clock!

3.6.1 Alarm clock epidemic
3.6.2 Insomnia trap
3.6.3 Wake up the President
3.6.4 Alarm clock monsters

3.7 Sleep inertia

3.7.1 What is sleep inertia?
3.7.2 Does sleep inertia show a circadian rhythm?
3.7.3 How can I recover from sleep inertia?
3.7.4 Can sleep impair learning?
3.7.5 Why naps cause sleep inertia?
3.7.6 Long sleep and sleep inertia

3.8 Health effects of shift-work and jetlag

3.8.1 Properly designed shift work
3.9 Excessive sleeping

4 Sleep habits

4.1 Body clock
4.2 Components of sleep in phase disorders
4.3 Lark-owl misconception

4.4 Charting sleep with SleepChart

4.4.1 SleepChart in SuperMemo
4.4.2 Sleep timeline in SleepChart
4.4.3 Sleep and learning timeline in SuperMemo

4.4.4 Circadian graph

4.4.4.1 Sleep initiation
4.4.4.2 Sleep maintenance
4.4.4.3 Optimizing bedtime
4.4.4.4 Example 1: Unstable circadian cycle
4.4.4.5 Example 2: Stable circadian cycle
4.4.4.6 Phase shift disorders

4.5 24-hour sleep cycle

4.5.1 Perfect 24-hour cycle
4.5.2 Sleep and stress
4.5.3 Monophasic sleep
4.6 Preference for night sleep

4.7 Biphasic nature of human sleep

4.7.1 Biphasic learning
4.7.2 Biphasic sleep periodogram
4.7.3 Biphasic learning and sleep
4.7.4 Biphasic graphs in SuperMemo
4.7.5 Monophasic sleep with biphasic learning
4.7.6 Biphasic circadian graph
4.7.7 Two components of biphasic sleep propensity
4.7.8 Biphasic performance in sleep deprivation
4.7.9 Summary: Napping is good!

4.8 Segmented sleep

4.8.1 Interpretation of segmented sleep
4.8.2 Segmented sleep and Borbely model
4.8.3 Segmented sleep and two-component model

4.8.4 Examples of segmented sleep

4.8.4.1 Example: Premature bedtime
4.8.4.2 Example: Nocturnal awakening caused by stress
4.8.4.3 Example: Intense exercise
4.8.5 Application of segmented sleep

4.9 Delayed Sleep Phase Syndrome (DSPS)

4.9.1 DSPS in teenagers
4.9.2 Solution to the DSPS problem
4.9.3 Is DSPS a disease?

4.9.4 Asynchronous DSPS

4.9.4.1 Combating phase shift
4.9.4.2 Resynchronizing the cycle
4.9.4.3 Social life in DSPS
4.9.4.4 DSPS: genes or lifestyle?
4.9.4.5 Chronotherapy and its perils
4.9.5 Synchronous DSPS

4.9.6 28 hour day schedule

4.9.6.1 28 hour day in DSPS

4.9.6.1.1 Conventional schedule in severe DSPS
4.9.6.1.2 28 hour schedule in severe DSPS
4.9.6.1.3 Free running sleep in severe DSPS

4.9.7 Curing DSPS and insomnia

4.9.7.1 Solution for insomnia, DSPS and N-24
4.9.7.2 DSPS and lifestyle
4.9.7.3 Implausible solutions
4.9.7.4 Plausible solutions
4.9.7.5 The algorithm
4.9.7.6 Outcome: Balanced 24h sleep cycle!
4.9.7.7 Summary

4.10 Advanced Sleep Phase Syndrome (ASPS)

4.10.1 Genes and lifestyle in ASPS
4.10.2 Example 1: ASPS and substance abuse
4.10.3 Example 2: Overmedication and daytime drowsiness
4.11 Phase shift graph
4.12 Correlates of sleep phase syndromes

4.13 Baby sleep

4.13.1 How to make babies sleep well?
4.13.2 Sleeping throughout the night
4.13.3 Development of a healthy circadian cycle
4.13.4 Co-sleeping as a circadian solution
4.13.5 Best timing for feeding
4.13.6 Child's own bed
4.13.7 What about the mom?
4.13.8 Why babies sleep so much?
4.13.9 Conclusion: Perfect formula for baby sleep

4.14 Insomnia

4.14.1 Insomnia vs. electricity
4.14.2 How to fall asleep faster?
4.14.3 Phase-shift based insomnia
4.15 Hypersomnia
4.16 Sleep apnea

5 Napping

5.1 Napping is good

5.1.1 Napping and evolution
5.1.2 Naps and brain power
5.1.3 To nap or not to nap? Nap!
5.1.4 Napping in the corporate world
5.1.5 Napping rulebook

5.2 Napping myths

5.2.1 Myth #1: Only lazy people take naps
5.2.2 Myth #2: A nap is a nap is a nap
5.2.3 Myth #3: Make sure you wake up from Stage 2 NREM
5.2.4 Myth #4: The circadian cycle can be ignored or abolished

5.3 Best nap timing

5.3.1 Circadian timing of naps

5.3.1.1 Phase 0: Waking time
5.3.1.2 Phase 3: Creativity time
5.3.1.3 Phase 5: Pre-siesta
5.3.1.4 Phase 7: Siesta
5.3.1.5 Phase 11: Evening
5.3.1.6 Phase 13: Pre-sleep
5.3.1.7 Phase 15: Segmented sleep
5.3.1.8 Phase 18-24: Night sleep
5.4 One nap per day is enough

5.5 Polyphasic sleep

5.5.1 The law of accelerating returns
5.5.2 The Uberman's Sleep Schedule
5.5.3 Polyphasic sleep
5.5.4 To sleep or not to sleep polyphasically
5.5.5 5 years since the Uberman Big Bang
5.5.6 Compression of sleep stages in sleep deprivation
5.5.7 Sleep and creativity: Less is more
5.5.8 Polyphasic sleep in babies
5.5.9 Ultradian oscillations in babies
5.5.10 Do Piraha people sleep polyphasically?

5.5.11 Polyphasic sleep: scientific challenge

5.5.11.1 Are early risers better at polyphasic adaptation?
5.5.11.2 Why so little research into polyphasic sleep?
5.5.11.3 Medical supervision of polyphasic sleep
5.5.11.4 My own polyphasic sleep trial

5.5.12 Charting polyphasic sleep

5.5.12.1 Source of data
5.5.12.2 Stampi yachting research
5.5.12.3 Polyphasic sleep attempt
5.5.12.4 Uberman sleep logs
5.5.12.5 Two-process sleep model vs. polyphasic sleep
5.5.12.6 Polyphasic rollercoaster
5.5.12.7 Free running circadian cycle in polyphasic sleep

5.5.13 Claudio Stampi

5.5.13.1 Polyphasic vs. creative lifestyle
5.5.13.2 Polyphasic Bible
5.5.13.3 Cognitive tests in polyphasic sleep
5.5.14 Sleep deprivation is like alcohol intoxication

5.5.15 Sleep debt and napping

5.5.15.1 PureDoxyk Law
5.5.15.2 Minimizing total sleep time
5.5.15.3 Optimum nap duration
5.5.15.4 Personality characteristics of irregular sleepers

5.5.16 Polyphasic geniuses

5.5.16.1 Buckminster Fuller
5.5.16.2 Leonardo da Vinci
5.5.16.3 Nepoleon Bonaparte
5.5.16.4 Thomas Jefferson
5.5.16.5 Benjamin Franklin
5.5.16.6 Winston Churchill
5.5.16.7 Thomas Alva Edison
5.5.16.8 Nikola Tesla

5.5.17 Sustainability of polyphasic sleep

5.5.17.1 Clock and Hourglass model of polyphasic sleep
5.5.17.2 The limits of the body clock training
5.5.17.3 Conclusion
5.5.18 Caffeine in polyphasic sleep
5.5.19 Polyphasic sleep mutants

5.5.20 Polyphasic sleep blogs

5.5.20.1 Polyphasic myths

6 Factors that affect sleep

6.1 Stress

6.1.1 Positive stress
6.2 Alcohol
6.3 Caffeine
6.4 Sleeping pills
6.5 Melatonin
6.6 Nicotine

6.7 Exercise

6.7.1 Exercise is good for sleep
6.7.2 What is the best time to exercise?
6.7.3 Formula for best exercise
6.7.4 Sleep is good for exercise
6.7.5 Sex and exercise differ
6.8 TV
6.9 Cannabis
6.10 Sex

6.11 Diet

6.11.1 Vegetarian diet
6.11.2 Sleep and glucose metabolism
6.11.3 Fasting
6.11.4 Combating jetlag with diet

6.12 Learning

6.12.1 Learning should help you sleep
6.12.2 Does learning increase total sleep?

7 Sleep and learning

7.1 Sleep length

7.1.1 Optimum length of sleep

7.1.1.1 Recommended 8 hours of sleep
7.1.1.2 Saving time with polyphasic sleep
7.1.1.3 Minimizing sleep time
7.1.1.4 Inefficiencies in the sleep control system
7.1.1.5 Length of sleep among users of SuperMemo
7.1.2 People who sleep less live longer?

7.1.3 Jim Horne and Daniel Kripke

7.1.3.1 Dr Horne
7.1.3.2 Dr Kripke
7.1.3.3 My own prejudice
7.1.4 Effects of sleep duration and sleep phase on learning
7.1.5 Sleep block length distribution

7.2 How sleep affects learning?

7.2.1 Why is sleep important for learning?
7.2.2 Sleep and learning research

7.3 Studying sleep and learning with SuperMemo

7.3.1 Long sleep results in poor learning?
7.3.2 Learning reduces the demand for sleep?
7.3.3 Approximating the sleep phase
7.3.4 Timing of repetitions
7.3.5 The impact of SleepChart

7.3.6 Recall vs. Consolidation

7.3.6.1 Recall

7.3.6.2 Memory consolidation

7.3.6.2.1 Correlation between recall and consolidation
7.3.6.2.2 Good learning days
7.3.7 Alarm clock vs. learning
7.3.8 Learning in free running sleep
7.3.9 Alertness multiplier
7.3.10 Learning overload
7.3.11 Alertness vs. learning

7.4 How learning affects sleep?

7.4.1 Impact of learning on sleep

7.5 Sleep and school

7.5.1 Sleepy kids learn little!
7.5.2 Excessive school workload
7.5.3 School hours and homeschooling
7.5.4 Sleep deprivation in kids
7.5.5 Poor recall on schooldays

7.5.6 Examples

7.5.6.1 Example #1: Long weekend sleep
7.5.6.2 Example #2: Phase 12 napping
7.6 Learning in alpha state

7.7 Learning during sleep

7.7.1 Lucid dreaming

8 Physiology of sleep

8.1 Why do we fall asleep?

8.1.1 Initiation of sleep

8.1.1.1 Homeostatic signal
8.1.1.2 Circadian signal
8.1.1.3 Integrating homeostatic and circadian signals
8.1.1.4 Not all scientists agree
8.1.2 Circadian cycle

8.1.3 Borbély model

8.1.3.1 Borbély model in practice
8.1.3.2 Borbély model and evolution
8.1.3.3 Three-process model

8.1.4 Phase response curve (PRC)

8.1.4.1 Changing the length of the circadian period
8.1.4.2 Phase-shifting neural inputs

8.1.5 Recursive phase response curve (rPRC)

8.1.5.1 Recursive PRC in DSPS
8.1.5.2 Recursive PRC and phase advance
8.1.5.3 Recursive PRC in polyphasic sleep
8.1.5.4 Chaotic phase-shifting input
8.1.6 Two-component model of sleep in SleepChart

8.1.7 REM rebound hypothesis

8.1.7.1 Kinky napping
8.1.7.2 REM deficit
8.1.7.3 Three components of sleep propensity
8.1.8 Sleep-wake flip-flop
8.1.9 Suprachiasmatic nucleus (SCN)
8.1.10 Dorsomedial Hypothalamic Nucleus (DMH)
8.1.11 Ventrolateral Preoptic Nucleus (VLPO)
8.1.12 Nucleus of the Solitary Tract (NTS)
8.1.13 Adenosine

8.2 NREM and REM sleep

8.2.1 NREM and REM alternations
8.2.2 Evolution of NREM and REM
8.2.3 NREM and REM deficits
8.2.4 NREM control

8.2.5 Neuromodulation in sleep

8.2.5.1 Growth hormone and cortisol
8.2.6 REM Homeostasis
8.2.7 Transition to REM

8.2.8 REM flip-flop

8.2.8.1 Models of REM flip-flop
8.2.9 Termination of sleep

8.3 Why do we need sleep?

8.3.1 Biological origins of sleep

8.3.2 Sleep theories

8.3.2.1 Theories that fail the shutdown test
8.3.2.2 Theories that pass the shutdown test
8.3.2.3 Sleep as a neural optimizer

8.3.3 Sleep and memory

8.3.3.1 NREM and memory

8.3.3.1.1 NREM and hippocampal cleanup
8.3.3.1.2 NREM and declarative memory
8.3.3.1.3 Sharp wave bursts and long-term memory
8.3.3.1.4 Detecting memory optimization with interference tests

8.3.3.2 REM and memory

8.3.3.2.1 REM and learning
8.3.3.2.2 REM as a form of neural training
8.3.3.2.3 REM and creativity
8.3.3.2.4 REM as a neural optimizer
8.3.4 Synaptic changes in sleep

8.3.5 Neural optimization in sleep

8.3.5.1 Hippocampal lesions
8.3.5.2 Temporally graded retrograde amnesia
8.3.5.3 Memory processing in sleep
8.3.5.4 Catastrophic forgetting
8.3.5.5 Two-stage memory processing in sleep
8.3.5.6 Optimizing memories
8.3.5.7 Garbage collection
8.3.5.8 Unihemispheric sleep
8.3.5.9 Problem solving in sleep
8.3.5.10 Conclusions
8.3.6 Not all scientists agree

8.3.7 Robert Vertes and Jerome Siegel

8.3.7.1 1. Sleep does not serve a role in declarative memory?
8.3.7.2 2. REM sleep deprivation does not lead to cognitive impairment?
8.3.7.3 3. Sleep-dependent enhancement of procedural learning has not been proven?
8.3.7.4 4. Learning in waking is far more significant than overnight enhancements?
8.3.7.5 5. Sleep models should be simple
8.3.7.6 How can random impulsations in REM make a sense in dreams?
8.3.7.7 Dr Siegel's theory of sleep
8.3.7.8 My personal bias
8.3.7.9 Olive branch
8.3.7.10 More reading for skeptics
8.4 Clock genes

9 Myths and facts

9.1 Length of sleep
9.2 Napping
9.3 Sleep inertia
9.4 Insomnia
9.5 Bedtime
9.6 Body clock
9.7 Sleep in children
9.8 Learning and creativity
9.9 Alertness
9.10 Alarm clock
9.11 Sleeping pills
9.12 Polyphasic sleep
10 Incremental writing
11 Acknowledgements
12 Glossary

13 Summary

13.1 ABC of sleep
13.2 Optimizing sleep
13.3 Sleep and learning
13.4 General
13.5 Children
13.6 Napping
13.7 Substances
13.8 Role of sleep
13.9 DSPS
13.10 Polyphasic sleep
13.11 Physiology of sleep
14 Sources
15 References

The good educator insists on exercise, play, and plentiful sleep: "the great cordial of nature."

— John Locke (1632-1704)

Foreword

It is everyone's dream to wake up fresh, happy, and ready for action on a daily basis. Sadly, in the modern world, only a small minority lives that dream. Yet the dream is within reach for most healthy people given:

a bit of knowledge, and a readiness to make some lifestyle sacrifice.

I hope that this article compiles all the basic ingredients of knowledge that are helpful in accomplishing refreshing sleep. As for the sacrifice, it is important to begin with the understanding that one cannot eat one's cake and have it too. Healthy sleep may be incompatible with some modern habits, some cravings, or some lifestyle choices. At worst, refreshing sleep may be incompatible with one's job or even long-term goals. Due to the latter fact, this article cannot provide a solution for everyone. Moreover, having a happy and fresh mind on a daily basis is a difficult thing to accomplish even with an arsenal of knowledge and full focus on good sleep. However, let me state it emphatically, good sleep on most nights is feasible for most people! This article was originally written a decade ago. I have always been interested in memory, learning, and sleep. In addition, in my job, sleep is as important as oxygen. As we all move deeper into the Information Age and Knowledge Economy, the issues discussed herein will become more and more important for each of us. After writing the original article, I had the great pleasure of getting in touch with hundreds of people experiencing various sleep problems. I came to see first hand how knowledge of sleep helps solve their problems. I could also see how the industrialized age lays obstacles in one's quest for good sleep and high productivity. I have witnessed a true epidemic of sleep phase disorders, an explosion of interest in polyphasic sleep, and an exponential increase in interest in the matters of sleep in general. Despite my pleas, many people just cannot avoid using an alarm clock, running all-nighters before exams, waking their kids cranky for school, popping pills before sleep, leaving babies in their cots to cry it out for sleep, etc. The picture would be pretty sad and alarming were it not for the fact that there is hope in knowledge. With a degree of determination, everyone can improve his, her, or their kids' sleep. This article is a compilation of the most important and the most interesting things about the biology of sleep. It is supposed to help you gain knowledge needed to achieve high quality refreshing sleep that will boost your mental powers. The article explains why sleep is vitally important for health and for the brain. It argues that sleep deserves highest respect, and that most people could get excellent sleep if they only followed the prescribed rules. Since writing the original Good sleep, good learning, good life, tremendous progress has been made in the science of sleep. My own work with tools such as SleepChart and SuperMemo has shed some interesting light on the connection between sleep and learning. As I kept addressing the progress in sleep science in minor articles and FAQs, some visitors to supermemo.com complained that valuable nuggets of information are dispersed throughout the site instead of being organized in a more encyclopedic manner in a single article. Here then comes a comprehensive compilation, in which I would like to retain the focus on practical knowledge that is helpful in achieving good sleep. However, I would still like to smuggle in some lesser known research findings that might be inspiring for an average reader and/or a scientist working in the fields of sleep, memory, and learning. If you believe I left out anything important that others should know, please let me know. As the article grew to be insanely long, you may wish to begin with the summary at the bottom of the article. And if even that is too long, here are the highlights:

respect sleep as your tool for high IQ and good learning free running sleep can help you resolve many sleep problems biphasic sleep schedule is probably the healthiest schedule for creative people do not wake up kids for school; if they cannot wake up in time, let them skip a class or two, or consider homeschooling let babies and young children sleep on demand, co-sleeping is a great idea (even if many pediatricians will tell you otherwise) exercise, learning, and sleep are your best tools for brain growth! avoid regulating sleep and alertness with substances, esp. sleeping pills, alcohol, illegal drugs, nicotine, and caffeine

Notes

Incremental writing: Due to the size of the material, this article was written using a technique called incremental writing. Incremental writing is helpful in organizing a large body of earlier writings into a single linear piece. The main advantage of incremental writing is a reasonable degree of coherence despite speedy processing of materials taken from disparate sources. Texts produced with incremental writing are particularly suitable for learning with the help of incremental reading as they produce small independent Wikipedia-style sub-articles. For a linear reader, however, this may mean a degree of bloatedness and an annoying repetitiveness of the main themes for which I apologize. If the size of the article is intimidating, you could try reading it incrementally (e.g. with SuperMemo 2004 Freeware)? References: Due to the volume of the material, I was not able to provide references for all statements included in the text. Some of these are common sense, some are common knowledge, others I took from memory or from SuperMemo without digging deep to the direct source. If you cannot find a reference for a particular claim, please let me know

Importance of sleep

Why understanding sleep is important?

Too few people realize how important sleep is! The alarm clock is an often-used fixture in an overwhelming majority of households of the modern world. By using electric lighting, alarm clocks, sleeping pills, and shift-work, we have wreaked havoc on the process of sleep.

Four examples of sleep logs that illustrate that modern human sleep patterns are as varied as snowflakes.

Over the last hundred years of the twentieth century, we have intruded upon a delicate and finely regulated process that was perfected by several hundred million years of evolution. Yet only recently have we truly become aware that this intrusion may belong to the most important preventable factors that are slowing societal growth in industrial nations! In a couple of years from now, we may look at alarm clocks and "sleep regulation" in the same way that we look today at other "great" human inventions in the league of cigarettes, asbestos materials, or radioactive cosmetics. Check this list below and see which applies to you:

I often have problems with falling asleep at the right time I often find it painful to get up in the morning due to sleepiness I am often awfully drowsy at school or at work I regularly cut my sleep by 2-3 hours as compared with what my body seems to need I use the alarm clock and truly hate it I drink buckets of coffee or coke I often take 2-4 hour naps in the evening for me, at least one of the above is a source of regular stress or reduced productivity

I bet that chances are around 90% you could subscribe to one of the above. Perhaps this is why you are reading this article. It is also highly likely you have already learned to accept the status quo, and you do not believe you can do much about it. This article may hint at some remedies. However, the bad news is that for a real solution you will probably need to change your family life, your work, your boss, or some social rules! Sleep isn't just a form of rest! Sleep plays a critical physiological function, and is indispensable for your intellectual development! Those who do not respect their sleep are not likely to live to their full mental potential! Modern society has developed a set of well-entrenched rules that keep sleep in utmost disregard. This has been driven to pathological levels in American society. Here are some bad rules that hurt sleep:

it is ok to use an alarm clock to cut sleep short it is ok to work in shifts it is ok to travel people around the world without much attention to the jet lag problem it is ok to save time by sleeping less and working more it is ok to pull kids out of bed in time for school it is ok to skip nights before important exams, etc.

Cutting down on sleep does not make people die (at least not immediately). It does make them feel miserable, but the ease with which we recover by getting just one good night of sleep seems to make sleep look cheap. Even the reports from the Guinness World Record attempt at sleeplessness (Randy Gardner's awakathon in 1964 lasted 11 days) trivialized the effects of sleeplessness. Many books on psychiatry and psychology still state that there aren't any significant side effects to prolonged sleeplessness! This is false! The Guinness Book of Records has since withdrawn its sleep deprivation category due to the involved health risks. In 1992, when Bill Clinton was running for president, he proudly admitted that he went 48 hours without sleep because he really wanted to become the next president. Former Senator Bob Dole "improved" the record in 1996 presidential campaign: We have been going 78 hours. We've got to go 96. We have been going around the clock for America. Dole's feat was matched by Vice President Albert Gore Jr., who kept campaigning for three days before the election day of November 7, 2000. After the election, Gore still kept on his feet by going into extra hours of the concede-retract cycle of his cliffhanger contest against Governor George W. Bush of Texas. When Barack Obama was asked about his most desired Christmas gift after over a year of campaigning for president, he answered without hesitation: 8 hours of sleep. The bad example of disrespect for sleep comes from the most important people in the nation! Yet some dramatic facts related to sleep deprivation have slowly come into light. Each year sleep disorders add $16 billion to national health-care costs (e.g. by contributing to high blood pressure and heart disease). That does not include accidents and lost productivity at work. For this, the National Commission on Sleep Disorders estimates that sleep deprivation costs $150 billion a year in higher stress and reduced workplace productivity[1]. 40% of truck accidents are attributable to fatigue and drowsiness, and there is an 800% increase in single vehicle commercial truck accidents between midnight and 8 am. Major industrial disasters have been attributed to sleep deprivation (Mitler et al. 1988[2])(incl. Three Mile Island, Chernobyl, the gas leak at Bhopal, Zeebrugge disaster, and the Exxon Valdez oil spill). It has been known since the 1920s that sleep improves recall in learning. However, only at the turn of the millennium, research by Dr Robert Stickgold, Associate Professor of Psychiatry at Harvard Medical School, has made international headlines. Dr Stickgold's research proves a fact that has long been known yet little appreciated: sleep is necessary for learning (Stickgold 2005[3])! With less sleep, we reduce the recall of facts we learned before or after a shortened night. Studying nights before an exam may be sufficient for passing the exam, yet it will leave few useful traces in long-term memory. The exam on its own replaces knowledge as the main purpose of studying!

By cutting down on sleep, we learn less, we develop less, we are less bright, we make worse decisions, we accomplish less, we are less productive, we are more prone to errors, and we undermine our true intellectual potential!

A change in societal sleep habits can spell a social revolution in learning, health, and productivity on a scale that few imagine! "Judging from history, it would seem that fundamental changes in the way we think about sleep will be required for policy changes that would protect society from sleepy people who make catastrophic errors in industry and transportation" (Merrill Mitler, PhD) I have studied student personalities among users of SuperMemo for over twenty years now. There are a couple of determinants that make a good, efficient and persistent student. Here are some characteristics of a person who is likely to be successful in learning:

highly optimistic sleeps well knowledge hungry stress-tolerant energetic, but able to slow down at the time of learning

Here are some unfortunate characteristics that do not correlate well with the ability to study effectively:

prone to depression or mood swings problems with sleep (esp. insomnia) high levels of stress hyperactive and unfocused low stress tolerance (smokers, abusers of mood altering substances, drinkers, etc.)

Sleeping well appears to be one of the most important factors underlying success in learning!

Why do we sleep?

For many years, the physiological function of sleep has not been clear. In most people's mind, sleep is associated with rest and time for mental regeneration. Restorative, protective and energy-conserving theories of sleep have been quite popular until quite recently, when it has become apparent that one long-lasting sleep episode with suppression of consciousness does not seem to be the right way for evolution to tackle depleted resources, toxic wastes, or energy conservation. For example, muscles do not need to shut off completely to get rest. The critical function of sleep is dramatically illustrated in experiments in which rats chronically deprived of sleep eventually die usually within 2.5 weeks (for more see: If you do not sleep, you die!). In evolutionary terms, sleep is a very old phenomenon and it clearly must play a role that is critical to survival. Only quite recently, it has been proven beyond doubt that the function of sleep is related to learning (not all scientists agree)! Researchers have long known about the importance of the hippocampus, a small brain organ, for memory formation. Yet it has always been difficult to find out what is special about the hippocampus that distinguishes it from other areas of the cerebral cortex that also show synaptic plasticity, i.e. the ability to store memories. A collective effort of a number of researchers resulted in the proposition of the concept of neural optimization in sleep (see the next section for a metaphorical explanation: Disk and RAM metaphor). Ground-breaking theories of Dr György Buzsáki and his two-stage model of memory trace formation have shed new light on what might actually be happening during sleep (Buzsáki 1989[4])(important: do not confuse this two-stage model with the two-component model of memory (Wozniak et al 1995[5]) or with the two-component model of sleep regulation (Borbely 1982[6]) below). Using his knowledge of neural networks, ingenious experiments on neuronal firing, and sophisticated mathematical analysis of spatiotemporal neuronal firing patterns, Buzsáki provided a good model explaining how the two components of sleep, REM and NREM sleep, work together to optimize memories. The hippocampus acts as the central switchboard for the brain that can easily store short-term memory patterns. However, these patterns have to be encoded in the neocortex to provide space for coding new short-term memories. This complex process of rebuilding the neural network of the brain takes place during sleep. Unlike rest or conservation of energy, this highest feat of evolutionary neural mathematics requires the brain to be shut off entirely from environmental input (in most animals)! This automatic rewiring is the main reason for which we sleep and why there is no conscious processing involved! During sleep, the brain works as hard as during SAT or GRE exams. It rewires its circuits to make sure that all newly gained knowledge is optimally stored for future use.

We sleep so that the brain can integrate new knowledge and form new associations. As we must sleep for our brain to continue its function, our body attached dozens of important processes to run in sleep as well. In simplest terms, in waking we use and burn, while in sleep we restore and synthetize. Sleep affects the function and health of the entire body.

Sleep is controlled by a complex set of brain nuclei. Interference with this system disrupts the function of sleep. For more see: Sleep control system

For more see:

Neural optimization in sleep Not all scientists agree.

Disk and RAM metaphor A metaphor can help understand the role of sleep and why alarm clocks are bad. We can compare the brain and its NREM-REM sleep cycles to an ordinary PC. During the day, while learning and experiencing new things, you store your new data in RAM memory. During the night, while first in NREM, you write the data down to the hard disk. During REM, which follows NREM in the night, you do the disk defragmentation, i.e. you organize data, sort them, build new connections, etc. Overnight, you repeat the write-and-defragment cycle until all RAM data is neatly written to the disk (for long-term use), and your RAM is clear and ready for a new day of learning. Upon waking up, you reboot the computer. If you reboot early with the use of an alarm clock, you often leave your disk fragmented. Your data access is slow, and your thinking is confused. Even worse, some of the data may not even get written to the disk. It is as if you have never stored it in RAM in the first place. In conclusion, if you use an alarm clock, you endanger your data. If you do not care about your intellectual performance, you may want to know that there are many other biological reasons for which using alarm clocks is unhealthy. Many people use alarm clocks and live. Yet this is not much different from smoking, abusing drugs, or indulging in fat-dripping pork. You may abuse your brain with alcohol for years, and still become president. Many of mankind's achievements required interrupted sleep. Many inventions were produced by sleepy brains. But nothing is able to change the future as much as a brain refreshed with a healthy dose of restful sleep.

Bad sleep kills and costs billions

Sleep deprivation is a killer! It kills precious life via airplane crashes, nuclear power station failures, car crashes, oil spills, etc. Sleep deprivation can change the course of history. Charles Lindbergh would have been just a footnote in history if he had failed to recover the Spirit of St. Louis from a dive caused by microsleep. Sleep deprivation has changed the future of nuclear fission and the future of oil exploration. Poor sleep kills as many people on the roads as alcohol. 1550 annual fatalities in the US can be attributed to drowsy driving. That's nearly an equivalent of six WTC collapse tragedies in a decade! Amazingly, as the pain and suffering is diluted in the population, drowsy driving does not nearly make as many headlines as a terrorist attack. At least a third of Americans have fallen asleep behind the wheel at least once! During the shift to DST in spring, car accidents increase by 9%. Sleep deprivation carries an astronomical cost to industrialized societies. There are zillions of hours wasted on unproductive learning in schools, and zillions of man-hours wasted on futile tossing and turning in bed. There is also a cost to grumpy behaviors and snappy outbursts. The quest for better sleep provokes desperate solutions such as the Uberman polyphasic sleep, "safe alarm" contraptions, hundreds of books and thousands of blogs with good advice on falling asleep fast, getting up early, or sleeping little. At the same time real solutions are simple and obvious! Read portions of this article and try free running sleep for at least a month to quadruple your knowledge about sleep and its potential to change your life for the better. We need to respect sleep, let kids sleep, design smarter night-shift schedules, and minimize sleep deprivation in jobs that weigh on life and death (e.g. the medical profession). In a comment to the conclusion of a sleep deprivation debate organized by the Economist, Karen M. wrote: "We don't get enough sleep, and we are not going to "change our ways" because there are already too few hours in most people's days to do things they enjoy. Call it a sad fact of life because that's what it is". Even though Karen attempted to represent the entire population saying "we", many readers of this article will disagree and do their best to get as much sleep as physiologically necessary. Otherwise my writing effort would not be needed. Good sleep makes us nicer, smarter, and saves lives! See: 10 Things to Hate About Sleep Loss from WebMD.

If you do not sleep, you die!

Nearly everyone has pulled an all nighter once upon a time. Even if this is often an unpleasant experience, it nearly always ends up with a 100% recovery after a single night of solid sleep. It is therefore a bit surprising to know that that a week or two of sleep deprivation can result in death! Sleep researchers constructed a cruel contraption that would wake up rats as soon as they fell asleep. This contraptions showed that it takes an average of 3 weeks to kill a rat by sleep deprivation (or some 5 months by REM sleep deprivation alone)(Rechtschaffen 1998[7]). Dr Siegel demonstrated brain damage in sleep-deprived rats (Siegel 2003[8]). Due to an increase in the level of glucocorticoids, neurogenesis in some portions of the brain is inhibited by lack of sleep[9]. In short, sleep deprivation is very bad for the health of the brain. Sleep deprivation is a well-known form of torture. Yet, for ethical reasons, the rat experiment could not be reproduced in humans (to its ultimate end). However, we have a rough idea as to the degree of human durability in sleep deprived state due to fact that we can study the effects of sleep disorders. One of them is fatal familial insomnia, in which a mutation causes the affected people to suffer from a progressively worsening insomnia that ends in death within a few months. Another example is the Morvan's syndrome in which an autoimmune disease destroys neuronal potassium channels that lead to severe insomnia and death (unless the disease progresses into remission). You may have heard of reports of people who do not sleep at all. These are certainly inaccurate or false. Those who report never sleeping are either boasting or experiencing a sleep state misperception that leaves them with an illusion that they do not sleep when resting in bed.

Brain's garbage collection Why is sleep deprivation fatal? Death of sleep deprivation is like death of an old age in general. Very often, multiple causes conspire to produce the final inevitable outcome. Probably nobody knows the exact answer to this mystery. However, research into the role of sleep gives us pretty strong hints. One of the most important functions of sleep is the re-organization of neural networks in the brain. During the day, we learn new things, memorize, acquire skills, figure things out, set new memories through creative associations, etc. After a long day of waking, the brain is full of disorganized pieces of information that need to be integrated with things we have learned earlier in life. Without this re-organization, the brain would harbor chaos, and would quickly run out of space to store new memories. This neural role of sleep is so fundamental that sleep deprivation affects nearly all functions of the body that are governed by the nervous system. Without a regular garbage collection, individual networks begin to malfunction. These initially minor malfunctions can add up to a serious problem for the entire organism. Most prominent effects of sleep deprivation are problems with thermoregulation, decline in immune function, hormonal changes (e.g. increase in glucocorticoids and catecholamines), metabolic changes[link: Sleep and Glucose metabolism], malnutrition, hallucinations, autonomic system malfunction, changes in cell adhesion, increase in inflammatory factors (e.g. IL-6, TNF, C-reactive protein, etc.), skin lesions, oxidative stress, DNA damage, etc. Those problems become serious enough to kill. Metaphorically speaking, if we compared a less developed organism to a WW1 bomber, we could imagine that the process of evolving into a human being is like acquiring the software needed to fly a B-2 bomber. Even though B-2 is ages ahead of a plane constructed during the life of Orville Wright, it is enough to plant a bug in its software to make it fall out of the sky. Human body in sleep deprivation is like a B-2 with a progressive software malfunction. It may be technologically advanced, it may be smart, and yet it is very vulnerable. The reliance on advanced software or neural function is always dangerous! Luckily, all we need to eliminate the danger is to just go to sleep every day. For more see: Neural optimization in sleep.

Sleep protection There is a second layer of trouble in sleep deprivation. Due to the importance of sleep, all advanced organisms implement a sleep protection program. This program ensures that sleep deprivation results in unpleasant symptoms. It also produces a remarkably powerful sleep drive that is very hard to overcome. Staying awake becomes unbearable. Closing one's eyes becomes one of the most soothing things in the universe. Are these symptoms a result of network malfunction? Definitely not. If they were, the drive to sleep might malfunction as well. Moreover, recovery from sleep deprivation would not be as fast, as easy, and as complete! Sleep protection program is there, and it can make the effects of sleep deprivation worse. Like a cytokine storm in an overzealous immune system, sleep protection program can potentially add to the damage caused by the network malfunction in sleep deprivation.

Anabolic sleep Last but not least, sleep has evolved to become a chief anabolic state of the organism. Without it, the body keeps using itself up, without much time to rebuild. Turning on anabolic state does not require turning off the consciousness, however, the time of night rest seems to be the best time for the body to do all the rebuilding. As we must sleep anyway, that anabolic functions became consolidated with other functions of sleep, and now may be indispensable. The anabolic state, and the nighttime increase in GH or testosterone, also affects the neural networks and the status of our "mind software". Hormonal changes stimulate and/or inhibit neural growth. Dr Michael Stryker, best known for demonstrating the role of sleep in brain development (Stryker et al. 2001[10]), says that nighttime hormonal changes may "play a crucial role in consolidating and enhancing waking experience"[11]. One of the leading causes of death in sleep deprivation seems to have been opportunistic bacterial infections caused by a decline in the immune function (e.g. no febrile response). That decline could be caused equally well by (a) poor neural control of the immune function or (b) straight effect of hypercatabolism. Whatever the cause, scientists have quickly figured out that application of antibiotics did not help much in preventing death from those infections. Sleep deprived rats would die anyway. The infection might speed up death that was otherwise inevitable.

Why do we die without sleep? It is impossible to quantify the contribution of those three factors to the fatal outcome of prolonged sleep deprivation:

network malfunction, or secondary effects of sleep protection program, or continuous catabolic state.

Even though the latter two could possibly be remedied pharmacologically, there is no way around network remolding in sleep. Researchers who hope to find a remedy against sleep are plodding a blind path. Without some serious nanotechnology bordering on science fiction, sleep is here to stay with human race for many years to come. Even though, sleep deprivation could kill, sleep is good news. It makes us smarter! We should all embrace the blessings of healthy unrestrained sleep. After all, there are few better things in life than a good night sleep after a well-spent day. Sleep should be listed among basic human rights!

Two components of sleep

Electric lighting and stress are the two chief culprits that have converted the natural process of sleep into a daily struggle for millions. In the new millennium, we can rarely hope to get a good night sleep without understanding the science and the art of sleep. Currently, the societal understanding of sleep and its functions is as dismal as the understanding of the health risks of cigarettes in the 1920s. A majority of the population inflict pain, misery and mental torture on themselves and their children by trying to regulate their sleep with alarm clocks, irrational shift-work patterns, sleeping pills, alcohol, caffeine, etc. For a chance to break out from unhealthy sleep habits, you need to understand the two-component model of sleep regulation. There are two components of sleepiness that drive you to bed:

circadian component - sleepiness comes back to us in cycles which are usually about one day long homeostatic component - sleepiness increases with the length of time we stay awake

Only a combination of these two components determines the optimum time for sleep. Most importantly, you should remember that even strong sleepiness resulting from the homeostatic component may not be sufficient to get good sleep if the timing goes against the greatest sleep propensity determined by the circadian component.

Circadian component There are around hundred known body functions that oscillate between maximum and minimum values in a day-long cycle. Because these functions take about a day's time to complete, the term circadian rhythm was coined by Dr Franz Halberg of Germany in 1959 (in Latin circadian means about a day). The overall tendency to maintain sleep is also subject to such a circadian rhythm. In an average case, the maximum sleepiness comes in the middle of the night, reaches the minimum at awakening, and again increases slightly at siesta time in the afternoon. However, the circadian sleepiness is often shifted in phase as compared with your desired sleep time. Consequently, if your maximum sleepiness comes in the morning, you may find it difficult to fall asleep late in the evening, even if you missed a lot of sleep on the preceding day. In other words, the optimum timing of your sleep should take into consideration your circadian rhythm.

Homeostatic component Homeostasis is the term that refers to maintaining equilibrium or balance in physiological and metabolic functions. If you drink liquids containing lots of calcium, homeostatic mechanisms will make sure that you excrete calcium with urine or deposit it in the bones. This is used to make sure your blood levels of calcium remain the same. Similar mechanisms are used to regulate overall sleepiness and its multiple subcomponents. The longer you stay awake, the more you learn, the more you think, the higher your tendency to fall asleep. On the other hand, caffeine, stress, exercise and other factors may temporarily reduce your homeostatic sleepiness. The homeostatic mechanism prepares you for sleep after a long day of intellectual work. At the same time it prevents you from falling asleep in emergencies.

Clock and Hourglass metaphor

A metaphor is useful in explaining the two components of sleep (for a more scientific explanation see: Borbely model). Deep in the brain, your body clock is running a 24 hours cycle of activity. Every 24 hours, metaphorically, the clock releases a sleepy potion that puts you to sleep (for details see: Why we fall asleep). If you try to sleep at wrong hours, without the sleepy potion, you may find it very hard to fall asleep. All insomniacs suffer from the lack of sleepy potion. If they go to sleep too early, before they get their fix of sleepy potion, they will toss and turn. Often for hours. You need to listen to your body clock to know the right moment to go to sleep. It is important to know that sleepy potion produced by the body clock is not enough to put you to sleep. The brain also uses the hourglass of mental energy that gives you some time every day that you can devote to intellectual work. When you wake up, the hourglass is full and starts being emptied. With every waking moment, with everything your brain absorbs, with every mental effort, the hourglass is less and less full. Only when the hourglass of mental energy is empty will you able to quickly fall asleep. To get a good night sleep, you need to combine two factors:

your body clock must be saying "time to sleep" (circadian component of sleep) your hourglass of power must be saying "no more mental work" (homeostatic component of sleep)

If your sleepy potion tries to put you to sleep but your hourglass of mental energy is full, you will be very groggy, tired, but you will not fall asleep. If, on the other hand, you try to sleep without the sleepy potion while the hourglass of power is empty, you may succeed, but you will wake up very fast with your hourglass full again. That will make sleeping again nearly impossible. Insomniacs go to sleep before the body clock releases the sleepy potion. When you wake up early with an alarm clock, you can hardly get to your feet because your body is full of sleepy potion, which begs you to go back to sleep. When you are drowsy in the afternoon, your hourglass of mental power might be almost empty. A quick nap will then help you fill it up again and be very productive in the evening. If you drink coffee in the morning, it helps you charge the hourglass and add some extra mental energy. But coffee combined with the sleepy potion produces a poisonous mix that engulfs your brain in sickly miasma. If you try to drink coffee to stay up in the night, you will feel like a horse kicked you in the stomach. That's the acme of a criminal attack on your brain's health.

The fundamental theorem of good sleep Let us now formulate the fundamental theorem of good sleep:

To get high quality night sleep that maximizes your learning effects your sleep start time should meet these two criteria: strong homeostatic sleepiness: this usually means going to sleep not earlier than 15-19 hours after awakening from the previous night sleep ascending circadian sleepiness: this means going to sleep at a time of day when you usually experience a rapid increase in drowsiness. Not earlier and not later! Knowing the timing of your circadian rhythm is critical for good night sleep

You should be aware that using the circadian component will only work when all its physiological subcomponents run in sync (as it is the case in free running sleep). People with irregular sleep hours and highly stressful lives may simply be unable to locate the point of ascending circadian sleepiness as this point may not exist! For a visual illustration of circadian and homeostatic components, see section Two-component sleep model in SuperMemo. For more on the two components of sleep see: Borbely model.

When good sleep might not come? You may be surprised to find out that your internal circadian oscillation is based on a period that is closer to 25 hours than to 24 hours! To be exact, it varies between individuals, seasons, and other daily factors such as stress, timing of sleep, timing of the light period, intensity of light, exercise, and many more. Usually it falls into the range from 24.5 hours to 25.5 hours. Most of us are able to entrain this 25 circadian rhythm into a 24-hour cycle by using factors that reset the oscillation. These factors include intense morning light, work, exercise, etc. German scientists have named these factors zeitgebers (i.e. factors that give time). As a result of the influence of zeitgebers, in a well-adjusted individual, the cycle can be set back by 30-60 minutes each day. However, the entrainment to the 24-hour cycle may come with difficulty to many individuals due to factors such as:

blindness (i.e. the inability to use the main zeitgeber: light) short-sightedness (i.e. reduced sensitivity to light zeitgeber) increased demand for sleep (e.g. as a result of intense learning, highly creative job position, exercise, etc.) stress endocrine disorders sleep disorders adolescence

A great deal of sleep disorders can be explained by entrainment failure (i.e. the failure to reset the 25-hour circadian rhythm to the 24-hour daylight cycle). In other words, in the interdependence between sleep disorders and entrainment failure, the cause-effect relationship will often be reversed! Due to the physiological function of sleep, which is the rewiring of the neural networks of the brain, we can naturally expect that the demand for sleep be associated with the amount of learning on the preceding days. This link may also explain a decreased demand for sleep in retirement due to a decrease in intellectual activity. This age-related drop in the demand for sleep is less likely to be observed in highly active individuals. For similar reasons, the entrainment failure can often be found among students during exams. It is not clear how much of this failure can be attributed to stress, or to the desire to do more on a given day, or to the actual increase in the demand for sleep.

Formula for good sleep

There is a little-publicized formula that acts as a perfect cure for people who experience continual or seasonal problems with sleep entrainment. This formula is free running sleep! Free running sleep is defined by the abstinence from all forms of sleep control such as alarm clocks, sleeping pills, alcohol, caffeine, etc. Free running sleep is a sleep that comes naturally at the time when it is internally triggered by the combination of your homeostatic and circadian components. In other words, free running sleep occurs when you go to sleep only then when you are truly sleepy (independent of the relationship of this moment to the actual time of day). Night sleep on a free running schedule lasts as long as the body needs, and ends in natural awakening. No form of sleep disruption is allowed. In particular, any use of an alarm clock is the cardinal violation of the free running sleep principle. The greatest shortcoming of free running sleep is that it will often result in cycles longer than 24 hours. This eliminates free running sleep from a wider use in society. However, if you would like to try free running sleep, you could hopefully do it on vacation. You may need a vacation that lasts longer than two weeks before you understand your circadian cycle. Even if you cannot afford free running sleep in non-vacation setting, trying it once will greatly increase your knowledge about natural sleep cycles and your own cycle in particular. You should also know that it is possible to entrain one's sleep to a desired sleep bracket (e.g. early rising). However, the entrainment requires iron self-discipline and the religious adherence to the entrainment rules.

Free running sleep

Free running sleep is sleep that is not artificially controlled to match our schedules and desires. It is a sleep without alarm clocks and sleeping pills. Mankind has practised free running sleep for as long as it existed. Our ancestors were gently encouraged to retire to bedtime at sunset, and would wake up naturally, probably after having spent no less than 8-10 hours in bed (see also Segmented sleep). All departures from that healthy practise were an imposition of culture, habit, religion, and/or tradition. Despite our ancestors' lives being fraught with danger, superstition, wars and disease, we should pause and ponder the marvellous impact of this naturally undisturbed sleep on their health. The arrival of fire and candlelight did not provide much incentive to stay up except for those few that have always had much to do in the evening: the first bookworms and artists. Only the genius of Edison and the like brought in the true sleep scourge: the electricity. With the wide dissemination of printed matter and electric lighting, millions would find their evening book far more interesting than sleep. Enter the web. In 2012 AD, we have an endless spectrum of entertainments and distractions that lure everyone away from bed and healthy slumber. More and more, we want to squeeze sleep into designer brackets. We wish to fall asleep at a specific time, and wake up at a specific time. Amazingly, a big chunk of the population does not realize that this is not possible without a detriment to health! Luckily, nearly everyone has the intuition that sleep is vital for healthy living. Those who would want to dispense with sleep altogether form a tiny minority. Nearly all creative people would wish to wake up fresh and ready for action. Preferably at a specified time. The same people wish to be less tired in the evening before sleep, and fall asleep instantly. Preferrably at a specified time. Let me then state it in bold print: If we exclude unhealthy techniques:

It is not possible to fall asleep whenever we wish. It is not possible to wake up whenever we wish. It is not possible to eliminate evening sleepiness.

However disappointing this might be, everyone would do better in life if those truths were assimilated. If we agree to wake up naturally at one's body's preferred time, it should be possible to be fresh and dandy from the waking moment. However, a decline in mental capacity over the waking day is inevitable. It is natural. Midday dip in alertness is also inevitable. And the optimum bedtime is hardly movable. If you try to advance it, you will likely experience insomnia. If you try to delay it, you will cut down on sleep and possibly wake up unrefreshed. If you try to wake up earlier than your natural hour, e.g. by employing an alarm clock, you will wake up with a degree of sleep deprivation that will affect the value of sleep for your learning and creativity. Don't be fooled by the illusive boost in alertness caused by the alarm clock. Yes. This happens to some people, some of the time. This perpetuates the myth that it is possible to wake up fresher with the ring of the alarm.

There is only one formula for healthy and refreshing sleep: Go to sleep only when you are very tired. Not earlier. Not later. Wake up naturally without an alarm clock.

This simple formula is called free running sleep. For many people, after years of sleep abuse, even free running sleep can be tricky. It will take a while to discover one's own body's rules and to accept them. You will know that you execute your free running sleep correctly if it takes no more than 5 min. to fall asleep (without medication, alcohol or other intervention), and if you wake up pretty abruptly with the sense of refreshment. Being refreshed in the morning cannot be taken for granted. Even minor misalignment of sleep and the circadian phase will take the refreshed feeling away. After months or weeks of messy sleep, some circadian variables might be running in different cycles and free running sleep will not be an instant remedy. It may take some time to regulate it well enough to accomplish its goals. It cannot even be excluded that after years of shift-work or jetlag, some brain cells in the sleep control centers might have died out making it even harder to achieve well aligned refreshing sleep. In addition to all these caveats, stress is one of the major factors contributing to destroying the fabric of sleep. In free running sleep, stress will make you go to sleep later, take longer to fall asleep, and wake up faster, far less refreshed. Combating stress is one of the most important things in everyone's life for the sake of longevity and productivity. Partners and spouses can free run their sleep in separate cycles, but they will often be surprised to find out that it is easier to synchronize with each other than with the rest of the world (esp. if they have similar interests and daily routines). If they are co-sleeping, one of the pair will usually get up slightly earlier and work as a strong zeitgeber for the other. The problem will appear only when the length of the naturally preferred sleep cycles differs substantially between the two. In such cases, instead of being a zeitgeber, the other person becomes a substitute for an alarm clock. Even if you are not convinced, you should try free running sleep to better understand the concept of the sleep phase, and how the sleep phase is affected by various lifestyle factors. You will often notice that your supposed sleep disorder disappears! Note that the free running sleep period is not solely genetic. Various factors in the daily schedule are able to shorten or lengthen the period. Of the obvious ones, bright light in the morning or melatonin in the evening may shorten the cycle. Exciting activities in the evening will lengthen it. The period changes slightly with seasons. It will also change when you leave on vacation. It often gets shorter with age. Try free running sleep to understand your own sleep parameters. This will help you synchronize with the rest of the world, or at least get quality refreshing sleep. Please read more about free running sleep in this article. Throwing away the alarm clock is not a panacea. You may need to learn a bit about the hygiene of sleep.

Should we free run our sleep?

As it will be discussed later, free running sleep can be used to solve a number of sleep disorders except for those where there is an underlying organic disorder that disrupts natural sleep mechanisms. However, you will often hear two arguments against adopting the use of free running sleep:

Argument 1 - free running sleep will often result in a day that is longer than 24 hours. This ultimately leads to sleeping in atypical hours. This seems to go against the natural 24-hour cycle of light and darkness. Less often, the cycle will be less than 24 hours Argument 2 - sleep can be compared to eating. Your body will always try to get more than it actually needs. This will result in spending more time in sleep than necessary. In other words, free running sleep is time-inefficient

Argument 1: Phase shifts It is true that free running sleep will often run against the natural cycle of light and darkness. However, the departure from the natural rhythm is a direct consequence of using electric lighting and modern lifestyle. Our ancestors could expect little but darkness and boredom past sunset. Prolonged darkness and boredom are quite efficient in lulling humans to sleep. If we stubbornly refuse to use electric lighting beyond a certain hour, we will still find it difficult to run away from the excitements of modern lifestyle. To shut your brain to sleep efficiently in the early evening you would probably need to quit your current job and pick some uninspiring one, give up your intense family life, give up your hobbies and interests, give up the Internet, evening TV, etc. We live more stressful and more exciting lives than our grandparents. Turning the lights off in the early evening would probably only be wasteful. Additionally, shortsightedness, the ailment of the information age, makes us less sensitive to the light zeitgeber and artificially prolongs the circadian cycle. There are a number of downsides to free running sleep. The worst shortcoming is a difficulty in establishing an activity cycle that could be well synchronized with the rest of the world. Stabilization of the cycle is possible with self-discipline in adhering to cycle-reset rules such as morning exercise, bright light, sleep protective zone in the evening, etc.

Argument 2: Excessive sleeping It is true that people who try to free run their sleep may find themselves sleeping outrageously long in the very beginning. This, however, will not last in a healthy individual as long sleep is a body's counter-reaction to various sleep deficits resulting from sleep deprivation. Unlike it is the case with foods, there does not seem to be any evolutionary advantage to getting extra sleep on days when we can afford to sleep longer. In the course of evolution, we have developed a tendency to overeat. This is a protection against periods when food is scarce. Adipose tissue works as a survival kit for bad times. However, considering the function of sleep, the demand for sleep should be somewhat proportional to the amount of new learning received on preceding days. In ancient times, we did not have exam days as opposed to lazy days. Consequently, the link between learning and demand for sleep is quite weak. The body clock will still make us sleep 7-8 hours on nights following the days of total inaction. Secondly, every extra minute of sleep might improve the quality of neural wiring in the brain. Sleep would better be compared to drinking rather than eating. We do not have much capacity to survive without drinking due to our poor water storage ability. Similarly, we cannot sleep in advance in preparation for a double all-nighter before an exam or important deadline. The claim that free running sleep increases the natural need for sleep is false! If you happen to sleep longer in free running sleep, it indicates that you were sleep deprived before running free. This longer sleep stage is transient. On occasion, if you go to sleep very early, you can also clock an excess number of sleeping hours. For more see Excessive sleeping. In my view, everyone should always free run his or her sleep unless it makes it impossible to function in society along one's chosen profession, specialization, education, etc., or where it makes it impossible to take care of the young ones.

Free running sleep is stressless Someone suggested that if any change is stressful, switching to free running sleep would be stressful too. The opposite is the case. Perhaps after an exclusion of the initial adjustment period in which people with lesser understanding of chronobiology make mistakes that may result in a decline in their sleep quality. Saying that any change is stressful is a generalization that goes too far. Changing your T-shirts daily does not imply stress. In addition, the degree of change is important. The same change can produce overstress or be a welcome factor in life depending on its degree. Letting your sleep free run does not imply any degree of stress, unless free running sleep itself produces changes in your schedule that might be stressful. If you eat your moderate meals frequently when you feel hungry, you are likely to experience less stressful change than when you eat them at pre-set lunch hours. Free running behaviors, by definition, free your organism to adapt behaviors to body's internal needs. As such, these can be considered anti-stress factors. It refers equally to sleep, eating habits, exercise, and other physiological needs

Free running sleep algorithm

Start with a meticulous log in which you will record the hours in which you go to sleep and wake up in the morning. If you take a nap during the day, put it in the log as well (even if the nap takes as little as 1-3 minutes). The log will help you predict the optimum sleeping hours and improve the quality of sleep. Once your self-research phase is over, you will accumulate sufficient experience to need the log no longer; however, you will need it at the beginning to better understand your rhythms. You can use SleepChart to simplify the logging procedure and help you read your circadian preferences. Go to sleep only then when you are truly tired. You should be able to sense that your sleep latency is likely to be less than 5-10 minutes. If you do not feel confident you will fall asleep within 10-20 minutes, do not go to sleep! If this requires you to stay up until early in the morning, so be it! Be sure nothing disrupts your sleep! Do not use an alarm clock! If possible, sleep without a bed partner (at least in the self-research period). Keep yourself well isolated from sources of noise and from rapid changes in lighting. Avoid stress during the day, esp. in the evening hours. This is particularly important in the self-research period while you are still unsure how your optimum sleep patterns look. Stress hormones have a powerful impact on the timing of sleep. Stressful thoughts are also likely to keep you up at the time when you shall be falling asleep. After a couple of days, try to figure out the length of your circadian cycle. If you arrive at a number that is greater than 24 hours, your free running sleep will result in going to sleep later on each successive day. This will ultimately make you sleep during the day at times. This is why you may need a vacation to give free running sleep an honest test. Days longer than 24 hours are pretty normal, and you can stabilize your pattern with properly timed signals such as light and exercise. This can be very difficult if you are a DSPS type. Once you know how much time you spend awake on average, make a daily calculation of the expected hour at which you will go to sleep (I use the term expected bedtime and expected retirement hour to denote times of going to bed and times of falling asleep, which in free running sleep are almost the same). This calculation will help you predict the sleep onset. On some days you may feel sleepy before the expected bedtime. Do not fight sleepiness, go to sleep even if this falls 2-3 hours before your expected bedtime. Similarly, if you do not feel sleepy at the expected bedtime, stay up, keep busy and go to sleep later, even if this falls 2-4 hours after your expected bedtime.

Cardinal mistakes in free running sleep do not go to sleep before you are sleepy enough - this may result in falling asleep for 10-30 minutes, and then waking up for 2-4 hours. Ultimately you can experience an artificial shift forward in the entire cycle! unless for natural reasons (no sleepiness), do not go to sleep well after the expected bedtime. This will result in missing the period of maximum circadian sleepiness. Your sleep will be shorter and less refreshing. Your measurements will be less regular and you will find it harder to predict the optimum timing of sleep in following days do not take a nap later than 7-8 hours from waking. Late naps are likely to affect the expected bedtime and disrupt your cycle. If you feel sleepy in the evening, you will have to wait for the moment when you believe you will be able to sleep throughout the night

Sleep logging tips In free running conditions, it should not be difficult to record the actual hours of sleep. In conditions of entrainment failure, you may find it hard to fall asleep, or wake up slowly "in stages". In free running sleep, you should be able to quickly arrive to the point when you fall asleep in less than 10 minutes and wake up immediately (i.e. without a period of sleep inertia). In other words, you can remember the hour you go to bed, add 5-10 minutes and record it as the hour you fell asleep. As soon as you open your eyes in the morning, you should record the waking hour. Usually you should not have any doubts if you have already awakened for good (as opposed to temporarily), and you will usually not fall asleep again (as it may be a frequent case in non-free running sleep). The graph below shows an exemplary free running sleep log in a graphic form:

An exemplary 5-month free running sleep cycle graph. In the picture, the average time of night sleep is 7 h 5 min, time before the midday nap is 7 h 48 min, the average nap takes 25 minutes and the time before the nap and the night sleep is 9 h 46 min. The whole cycle adds up to 25 hours and 4 minutes. Note that the distance between the nap and the night sleep in the graph is less than 9 h 46 minutes due to the fact that the blue retirement-line refers to the previous day sleep as compared with the red nap-line. Consequently, the nap-to-sleep band is horizontally shortened by 64 minutes, i.e. exactly as much as the daily phase shift in the cycle.

If you have collected your own free-running sleep data with SleepChart, I would be very grateful for your submissions that will be useful in further research (sending data from SleepChart takes just a single click).

Optimizing the timing of brainwork

Circadian graph and brainwork The following exemplary circadian graph was generated with SleepChart using a log of free-running sleep:

The horizontal axis expresses the number of hours from awakening (note that the free running rhythm period is often longer than 24 hours). Light blue dots are actual sleep episode measurements with timing on the horizontal, and the length on the left vertical axis. Homeostatic sleepiness can roughly be expressed as the ability to initiate sleep. Percent of the initiated sleep episodes is painted as a thick blue line (right-side calibrations of the vertical axis). Homeostatic sleep propensity increases in proportion to mental effort and can be partially cleared by caffeine, stress, etc. Circadian sleepiness can roughly be expressed as the ability to maintain sleep. Average length of initiated sleep episodes is painted as a thick red line (left-side calibrations of the vertical axis). Mid-day slump in alertness is also circadian, but is biologically different and results in short sleep that does not register as red sleep maintenance peak. Sleep maintenance circadian component correlates with (but is not equal to): (1) negatively with: temperature, ACTH, cortisol, catecholamines, and (2) positively with: melatonin and REM sleep propensity. For more details see: Circadian graph and Biphasic nature of human sleep.

Best brainwork time Optimum timing of brainwork requires both low homeostatic sleepiness and low circadian sleepiness. There are two quality alertness blocks during the day: first after the awakening and second after the siesta period. Both are marked as yellow blocks in the graph (above). For best learning and best creative results use these yellow blocks for brainwork. Caffeine can only be used to enhance alertness early in this optimum window. Later use will affect sleep (caffeine half-life is about six hours). Optimum timing of exercise may vary depending on your exercise goals and the optimum timing of zeitgebers (e.g. early morning for DSPS people and evening for ASPS people). In this example, the stress block is followed by the exercise block to counterbalance the hormonal and neural effects of stress before the siesta. Unmarked white areas can be used for the lunch (before siesta) and fun time unrelated to work in the evening at a time when the ascending circadian sleepiness makes creative work ineffective. That white evening protective zone should be free from stress, alcohol, caffeine, etc. Recommended activities might include fun, games, relaxation, TV, reading, family, DIY, housework, etc. For inveterate workaholics, less challenging and stress-free jobs might also work ok. The best litmus test for a well designed day is that all activities should be fun! Brainwork is fun only if your brain is ready. Sleep is fun if you are ready. Rest and entertainment feel in place only after a productive day. Even a bit of stress can be fun if it is properly dosed and timed. You do not need to be an adrenaline junkie to enjoy your stress and exercise slots. There is little exaggeration in saying that a good understanding of the circadian cycle is the key to a happy and productive day!

Balanced 24 hour cycle The slanting green line separates the graph into the areas of phase advanced (right) and phase delays (left). The line is determined by points in the graph where the waking time (horizontal axis) added to the sleep time (left vertical axis) equals to 24.0 hours. The place where the green breakeven line crosses the red sleep length line determines the optimum balanced sleep cycle of 24 hours. In the presented example, 17.35 hours of waking, added to the expected 6.65 hours of sleep time complete a balanced full 24 hours sleep-wake cycle. The greater the angle between the green and red lines, the harder it is to balance sleep and fit it into the 24h cycle of the rotating earth. In the example, adding waking hours does not shorten sleep much enough to make the balance easy. This implies that a religious adherence to a 17.35 day may be necessary to balance the cycle. However, this shortened waking day may increase sleep latency and increase the probability of premature awakening, which can also tip the balance towards the phase delay. The vertical aqua line shows where the expected sleep time added to the waking time equals to 24 hours (crossover with the green line representing a perfect 24-hour day). In DSPS or ASPS that 24h balance may be hard to accomplish. For example, without medical intervention, only a large protective zone in the evening, early nap (or no nap), and intense morning exercise can help balance the day in DSPS. Important! This graph is based on data that is true solely for a free running sleep condition. If you use an alarm clock to regulate the timing of your sleep, this measurements and recommendations may not apply! In addition, timing and the amplitude of changes differ vastly between individuals!

Sleeping against your natural rhythm

If you sleep against your natural rhythm you will often experience tiredness or drowsiness that can be resolved by adjusting the sleeping hours. In healthy individuals, the daytime alertness is primarily determined by:

circadian phase and homeostatic sleepiness total sleep time the night before amount of slow-wave sleep the night before regular adherence to the sleep-wake schedule in preceding days sleep deficits accumulated in the preceding days (e.g. REM deficit, SWA deficit, etc.)

All those factors are closely associated with the sleep phase. Free running sleep provides the best way to maximize the alertness throughout a waking day. Free running sleep is likely to shift the minimum temperature point from the early morning closer towards the middle of the subjective night. You should notice increased sleepiness before going to sleep and no sleep inertia upon awakening! If you cannot free-run your sleep, it is very important to understand the relationship between your homeostatic and circadian sleep drives as compiled in the table below. In the course of the day, you should move in sync between the yellow areas of the table, i.e. from perfect alertness to maximum sleepiness, and then back to perfect alertness. The gray areas illustrate when your sleep falls out of sync:

High circadian sleepiness

Low circadian sleepiness

High homeostatic sleepiness

Peak of the night: You are very drowsy and fall into refreshing sleep with latency of less than five minutes

Insomnia: You are tossing and turning in bed. You are very tired but you cannot fall asleep. Your temperature, blood pressure and pulse are raised. Your thoughts are racing Solution: Wait for the arrival of the circadian phase. Delay going to sleep by 3-6 hours

Low homeostatic sleepiness

Hypersomnia: You are drowsy throughout the day despite long sleep hours. Napping does not help. You show minimum energy levels. Your muscles are weak and atonic Solution: Adjust your sleep phase to your circadian (e.g. try to go to sleep 3-6 hours later)

Peak of the day: You are alert, energetic, and full of new ideas

Kill the alarm clock!

Alarm clock epidemic Few upwardly mobile people in the modern rat-race society can live without an alarm clock. With a shot of strong coffee and round-the-clock stress, most people learn to live and survive with an alarm clock. Half of the population wakes up with an alarm, 9% are woken by a partner, 4% by pets, 3% by children, etc. That leaves a minority that wake up naturally. Increasingly, time becomes the most precious commodity in society where achievement is often associated with speed and perfect time-management. However, alarm clocks introduce harmful side effects: stress, sleep debt, and worst of all, disruption of the natural physiological sleep function. At worst, those factors will result in physical damage to the brain (e.g. such sensitive structures as the hippocampus, your memory switchboard, may literally lose neurons as a result of disrupted sleep). The art of time-management makes it possible to live at a high speed with an alarm clock at your side, and still be free from stress. However, the societal damage inflicted by alarm clocks and sleep deprivation is unforgivable. An alarm clock that interrupts your sleep damages your memories, your ability to learn, your creativity, your mood and temper, your relationships with other people, your ability to focus, and your overall intellectual performance! Dr Robert Stickgold has showed that people, who learn a skill during the day, do not show significant improvement until they get a sound 7-8 hours of properly structured sleep[3]. There was a noticeable correlation between the degree of improvement and the quality of sleep received. My own work with SleepChart also shows that the use of alarm clocks can dramatically reduce memory recall and consolidation. Forgetting is so painless that we rarely notice its effects. In a natural way, forgetting will proceed even if you get as much sleep as you need, and it is difficult to point to specific memories lost as a result of not sleeping enough. Moreover, sleep deprivation may leave your memories intact while their storage will be sub-optimum. The difference may be impossible to spot without measurement. We are more likely to notice sleepiness, reduced mental agility, or bad mood. Disrespect for sleep has reached biblical proportions. This is most noticeable in the US, and other highly industrialized nations. Men's Health's Dan Vergano writing for ABC News in "No More Rude Awakenings" suggests a seven-day system for fighting sleepiness: "The secret is to fuel that arousal system so it can beat the pants off the sleep system. By creating the kind of feel-good expectations that trigger hormones to wake the brain, you’ll override the need to sleep and be able to jump out of bed like a man on fire". The article suggests a "fresh" mind method that capitalizes on the fact that stress hormones help keep you alert. However, there is a simple and the only rational remedy for "rude awakenings": get enough sleep! Jumping like a man on fire is not likely to have a positive effect on your creative potential! You may often notice that waking up with an alarm clock gives you a quick start into a day. You may then come to believe that using the alarm clock might help you keep alert later during the day. This is not the case. The alarm signal simply scares your brain into wakefulness disrupting the carefully planned process of neural optimization that occurs in sleep. As a result, you get an immediate injection of adrenaline and your levels of ACTH and cortisol also increase. This is cortisol that peaks at awakening in natural sleeping rhythm that provides you with the fresh-mind impression. With passing time, this cheaply gained alertness will wear thin unless you continue abusing your physiology with more "remedies". You may use more scare tactics for keeping yourself alert, abuse caffeine, or even get a more profound effect with modafinil, cocaine, or amphetamines. Alertness should be achieved with the help of sufficient sleep, not despite the lack of sleep! Apart from your reduced ability to learn new things, all unnatural anti-drowsiness methods will produce a great deal of side effects that can be pretty damaging to your health in the long run. All efforts to overcome sleepiness by means other than sleep itself can be likened to a chase of the first high in the use of psychoactive substances. If you drink buckets of coffee, do pushups, pour cold water over your head, or slap your face, you only dip into the last reserves of your alertness hormones that only worsen the effects of deprivation after the effects of the stimulation wear off, which is usually a matter of minutes. Rarely can you get a boost lasting more than an hour, and the more you perk up, the lower you fall in the aftermath.

Insomnia trap If your life without an alarm clock may seem like an impossibility, you will probably need to use all methods in the book to be sure you get enough sleep and minimize the damage. If you need to wake up early at the cost of your brain, avoid the insomnia trap! Insomnia trap is a vicious circle of:

going to sleep too early to get more sleep, failing to fall asleep in time (or worse, waking up prematurely), feeling even more tired on the next day, and going to sleep even earlier on the next day to catch up with the lost sleep.

It is better to go to sleep at a natural hour (i.e. a bit later), wake up early, suffer a degree of sleep deprivation, and hope for a phase reset that will make it possible to continue on the designer schedule. For a solution to the insomnia trap see Curing DSPS and insomnia. If you cannot reset your phase and still feel tired when getting up early on a regular basis, consider choosing a job that is acceptable for your body, not the other way around. Your long-term health and well-being is at stake. If you absolutely cannot live without an alarm clock, you can at least start from changing your mindset about the importance of sleep and ensure you do not impose wrong habits on your children. Perhaps the young ones will be lucky enough to work in a flex-time system that will make it possible to get sufficient amount of undisturbed sleep. At least, do not set a bad example!

Wake up the President President Bill Clinton was woken up twice by telephone during the night of April 22, 2000 before the infamous I.N.S. raid on the home of Miami relatives of the young Cuban exile Elian Gonzales. He was probably the most often disrupted and sleep deprived president in history. Only after a heart surgery did Clinton take diet, sleep and (real) exercise seriously. Those interrupted nights would definitely influence his performance and the quality of his decisions! Has anybody thought of a rule: Do not wake up the president? A rule that could only be revoked in a true national emergency? President G. W. Bush (b. 1946) was woken up when an American spy plane landed in China in 2001. He was also woken up after a suicide bombing in Jerusalem in 2002. George H. W. Bush (b. 1924) and Hilary Clinton made "waking up in the middle of the night" part of their presidential campaign and prowess. It seems that only Ronald Reagan had pretty strong rules for protecting his own sleep. He also famously napped during some cabinet meetings. He slept through a couple of international events without an apparent negative impact on his somewhat delayed decision-making. Critics would say he slept through the entire Iran-Contra affair. Was Reagan so protective of sleep because he understood the role of sleep better, or perhaps he was just a bit lazier than other presidents? I don't know. However, he sure set a good example.

Alarm clock monsters Andrea K. wrote to me with skepticism: "Take the alarm clock away from a typical person and they won't just wake up on their own at their desired time and they will miss work, school, or whatever. An alarm clock can't be that bad for you because of the simple fact that most people use it and I never noticed any problem with them :) Everyone in my family has been using one since they were children, and no one suddenly went crazy or began to mutate into a monster (yet)!" As I wrote earlier, when you use an alarm early in the morning in order to get to work or to school, you cut off the later stages of sleep. If the intrusion into natural sleep is not large (e.g. from minutes to an hour), the damage may be limited. Alarm clock will do far more damage if it cuts deep into the middle of the night sleep. You can compare the use of alarm clocks to smoking or eating hot dogs. The harm is not great enough to be instantly noticeable. It took the public many years to largely accept that "smoking is bad" or "fast food is bad". It is hard to quantify the degree of damage. However, as we move to knowledge society where our intellectual performance becomes increasingly important, the effects of sleep deprivation will come under closer scrutiny and alarm clocks are bound to gradually fall out of favor. Unlike hot dogs, they are already universally hated by their users. Most people are able to somewhat adapt their sleep to their schedules if their routines are regular enough. When those people need to resort to the use of the alarm clock, they cut less of their sleep and the damage is proportionally smaller. Nevertheless, we should always strive at eliminating alarm clocks altogether. Most of all, we should protect our kids from suffering interrupted sleep!

Sleep inertia

What is sleep inertia? Sleep inertia is the feeling of grogginess that may follow sleep. There are different types of sleep inertia and there is a monstrous confusion in terminology, as well as a great deal of confusion between different types of sleep inertia in scientific literature. An example of a confusing definition of sleep inertia: "Sleep inertia refers to the feeling of grogginess most people experience after awakening". A more appropriate definition would say "Sleep inertia refers to the feeling of grogginess that is a result of interrupted sleep or other violations of sleep hygiene". Most of all, sleep inertia is not an inevitable part of sleep in humans. In healthy individuals, sleep inertia is a direct result of errors in the art of sleeping. With a religious adherence to the principles of sleep hygiene, you need not ever experience sleep inertia and its negative consequences for learning, attention, health, etc. All research into sleep inertia should clearly distinguish between its different types:

interrupted deep sleep - in the exemplary hypnogram, we can see Stage 4 NREM setting in after some 30 min. of sleep. Waking up a sleeping subject at this stage is particularly difficult. When woken from deep sleep, we experience an overwhelming need to get back to sleep. The feeling can be compared to being hit on the head with a heavy object. The brain is in a state entirely unsuitable for processing waking information. This is the torture that many polyphasic sleepers impose on themselves by trying to interrupt "naps" taken in their subjective night phase. interrupted REM sleep - in the hypnogram, REM sleep is marked in blue and its occurrence increases towards the end of night sleep. Interrupting fully-blown REM sleep is equally unpleasant. Yet the neurohormonal state of the brain is entirely different than that when the deep sleep is interrupted. One of the easily recognizable hallmarks is muscle weakness. Due to the function of REM, the motor system is turned off in this phase. If you were to test your strength on a hand gripper, you might score less than your kids. Interrupted REM is also frequently associated with dream recall. As soon as the brain returns to its typical waking mode, REM dream memories dissipate very fast. If you do not write down your dream instantly, it may be unrecoverable from memory as soon as 5 min. later. waking in a wrong phase - even natural waking can result in sleep inertia. If you wake up naturally in the period of your subjective night sleep, you may feel pretty groggy for a while. The main cause of premature waking is an early bedtime. Sleeping in an early phase is pretty widespread. Many people need to wake up early against their body clock. They will often use various remedies to fall asleep early (from alcohol to sleeping pills). As a result, they will fall asleep early, wake up early, and seemingly get "sufficient" sleep while still feeling tired and unrefreshed. This is because they wake up while their body is still, in circadian terms, in the period of the subjective night. Early bedtime will often result in insomnia. However, when sleep is initiated successfully, the sleep control system can launch an equivalent of night sleep ahead of time. Such sleep may run its course and even last a bit longer. However, its structure will differ, and the morning circadian sleep propensity will still not be fully cleared on waking. As a result, morning grogginess will result as a combination of circadian sleepiness and various sleep deficits caused by a change in sleep structure (e.g. REM deficit). Inertia caused by early waking is far easier to combat than interrupted NREM or REM sleep as it largely dissipates with the expiration of the circadian sleep propensity. However, minor sleep variable deficits may last for the course of the day. For some people, sleeping in a wrong phase is so much of a daily reality that they tend to forget what a crisply alert mind is, and, as in the mis-definition quoted above, they tend to think this is the "type of sleep inertia most people experience", as if it was part of normal human physiology. They might dismiss it by saying "I am just perpetually tired. It is just me". Technically, the definition of sleep inertia should also be extended to the brain state caused by a major delay in bedtime. That brain state is similar to the inertia caused by early waking. It may feel more natural as it combines both components of sleep propensity: homeostatic and circadian sleepiness. Instead of feeling like inertia, it will feel like severe sleepiness that might verge onto nausea. That type of inertia is particularly dangerous for drivers as it only gets worse in time and may results in moments of microsleep when portions of the brain cortex simply enter the sleep mode with the appearance of theta waves in the EEG.

Does sleep inertia show a circadian rhythm? This question does not have a straight answer. Whatever you read on the subject, make sure you deconvolve the all-encompassing term "sleep inertia" and ask the same question for each of the types of sleep inertia. If you interrupt deep sleep, it will always feel bad. The degree of that feeling will likely depend on the depth of sleep, your homeostatic status and, to a lesser degree, your circadian status (only because deep sleep is largely homeostatic). However, if you interrupt REM sleep, it is more likely to have a more profound effect at the times of the circadian REM peak. Finally, the wrong-phase inertia is purely circadian. It will hit you only in the periods of your subjective night, and it will dissipate on its own at time of your subjective day.

How can I recover from sleep inertia? You can google out dozens of remedies against sleep inertia (example), and you might be amazed that there is a big wide hole in reasoning behind all that "Internet advice", which often fails to notice that: well-timed sleep is the best remedy against all forms of sleep inertia! For interrupted sleep inertia, NREM or REM, the simple remedy is: go back to sleep. The more powerful the inertia, the greater your chances of quickly falling back asleep. Remedies like coffee or exercise might make you feel better (or not), but they can do their own damage. If your profession calls for waking up in the middle of the night, remember that you are doing the service at the cost of your own health and longevity. Wrong-phase inertia is a bit harder to combat. In many cases you won't be able to fall asleep. Even worse, trying to sleep can sometimes make things worse. The best solution is to suffer through the discomfort, avoid napping till your next subjective night period, and go to sleep in the right phase. Most of the time, sufficiently long wakefulness and hitting the right phase will help you instantly synchronize all sleep variables. However, in some cases, circadian ripples may drag for days, esp. if you are not too fluent in computing your correct sleep phase. If you do lots of shift-work or intercontinental flying, it is very easy to be confused about when your subjective night time occurs. In such cases, you could use SleepChart Freeware to get some visual support that makes a guess easier.

Can sleep impair learning? Amazingly, the confusion into the types of sleep inertia has been responsible for yet another myth: sleep before learning increases forgetting! Well-timed sleep will not cause sleep inertia and will not contribute to a decline in learning. Just the opposite, it is 20-60 min. after natural waking when the learning results are best. Naturally, this is only true in free running sleep. All too often, alarm clocks are used to interrupt the night sleep and the early morning is pretty unconducive for learning.

Why naps cause sleep inertia? Naps will cause sleep inertia only if they are taken:

too late, or in conditions of severe sleep deprivation, or in conditions of REM sleep deficit.

All those three conditions can fool the sleep control systems into thinking that the nap is the opportune time for launching a full-night sleep episode. If an attempt to launch full-blown sleep takes place long before the main circadian low (nighttime acrophase), you may wake up prematurely with the sense that you got an incomplete and unrefreshing nighttime sleep. Such sleep will leave you groggy and will make it harder to initiate proper sleep during the subjective night. To avoid sleep inertia associated with napping then, avoid sleep deprivation in the first place, and read about the optimum time window for napping.

Long sleep and sleep inertia Many people believe that long sleep causes sleep inertia, headaches, etc. The root cause of problems that follow long sleep is prior sleep deprivation or sleeping in a wrong phase. Unusually long sleep is simply not possible in a healthy individual on a free running schedule. It is usually a severe sleep deprivation that makes it possible to fall asleep well ahead of the optimum circadian bedtime. The unusually long sleep will then carry through the subjective evening and the entire subjective night, adding up to some highly unusual sleep totals (12-18 hours). Such sleep is often followed by a state that is reminiscent of sleep inertia (the "worn-out" syndrome). No wonder it is easy to build a wrong association between long sleep and sleep inertia. It is very difficult to persist in a long-sleep routine, since the sleep-regulating mechanism will quickly bring the length of sleep to a more typical range. On one hand, the "worn-out" syndrome might seem to persist if the sleep period is wrongly adjusted to the circadian cycle. On the other hand, the "worn-out" observation is usually produced by those who cannot get enough sleep during the week and then sleep long on the weekend. In the latter case, follow-up observation is often impossible due to the next week's obligations. This deepens the wrong conviction that too much sleep is harmful. Healthy individuals cannot get "too much sleep"! Their brain will simply produce natural waking up at the right time. Drs Jim Horne and Daniel Kripke may claim otherwise. Perhaps they never tried to nod off at a peak alertness window?

Health effects of shift-work and jetlag

Nearly 20% of the population in the industrialized nations is involved in shift-work! Surveys show that only 10% of the shift-working population have no complaints about the negative impact of their sleep schedules on their health and life[12]. With well-designed shiftwork, those numbers could look much better. This would not, naturally, change the fact that all forms of sleep regulation are risky and potentially unhealthy. Research shows that shift-workers suffer from various gastrointestinal and cardiovascular problems. Cardiovascular changes might be mediated by inflammatory markers such as C-reactive protein. Many have problems with achieving refreshing sleep. After many days of chronic sleep restriction, a significant degree of cognitive decline accumulates. This decline leads to levels that in the end approach those found in severe acute total sleep deprivation. Substance abuse among shift-workers is also much higher than average. Seemingly minor problems such as headache, inattention, decline in libido, fatigue, irritability, etc. all add up to pretty miserable life for a vast majority of workers on a poorly designed shift schedules. The set of problems affecting shift-workers is pretty familiar to researchers studying jetlag. Separate medical terms have been coined for the two related sets of symptoms: shift work disorder (SWD) and jet lag disorder (JLD). The most dramatic finding in reference to jetlag was the loss of cells in the hippocampus in flight attendants who were employed for longer periods in jobs involving intercontinental flights (Cho 2001[13]; Cho et al. 2000[14]). We can surmise that the exactly same health issues (times ten) would affect polyphasic sleep adepts if they could only last on their schedule long enough. In addition to the direct effects of sleep phase misalignment, there is also a degree of sleep deprivation in shift-work and jetlag. Sufficient sleep is important for proper glucose metabolism and prevention of obesity and type II diabetes. Sleep restriction decreases the levels of leptin and has an opposite effect on ghrelin. Those two appetite hormones, as a result, make sleep deprived individual feel hungrier than well-rested individuals and shift upwards the set point of body fat weight in the caloric balance homeostat. Restricting sleep to 5 hours per night causes some 20% change in the levels of these appetite control hormones. This change corresponds to some extra 1000 kcal in free running feeding, or over 3 kg of fat per month in energy terms. Sleep restriction can easily halve insulin sensitivity leading to type 2 diabetes. It also significantly increases the risk of hypertension, stroke, heart attack or kidney failure (Van Cauter et al. 2007[15]). Other hormonal changes include increase in thyroid hormone levels (Allan and Czeisler 1994[16]), prolactin, LH, and estradiol (Baumgartner et al. 1993[17]). Finally, the root cause of many phase shift problems is a complex impact of shift-work and jetlag on the circadian changes in the level of the stress hormone cortisol. The net effect of the impact of cortisol level changes is the hypercatabolic state that effectively results in the body "eating itself up" in the long run. This way, when neglecting your body clock, you can become obese and biologically "wasted" at the same time. In 2007, the International Agency for Research on Cancer issued a statement saying "Shiftwork that involves circadian disruption is probably carcinogenic to humans". Using the term "carcinogenic" is probably slightly misleading as the actual cause of increased cancer in shift-workers is probably related to the decline in the immune function and the body's natural ability to fight off mutating cancer cells. However, the statement is important as it seals the fate of shift-work and jetlag, which should ultimately fall into the category of long-term health risk factors that cause wide ranging and serious systemic health problems.

Poorly designed shift-work, jet lag, and sleep deprivation are all serious systemic health risks that affect your well-being and longevity.

For more about the tiny and delicate structure of the body clock, see the section devoted to the suprachiasmatic nucleus.

Properly designed shift work I often qualify shift-work as a health risk with the designation "poorly designed". This is because it is possible to design schedules for a group of people where the circadian disruption is minimum. Using chronotherapy it is possible to gradually phase in employees into working through the night. The chief principle of such a therapy is that phase shifts should not exceed one hour per day and should, with few exceptions, be forward shifts (i.e. shifts where the days are longer than 24 hours, not shorter). All therapies that depart that principle and involve leisure time, napping, bright light, melatonin, sleeping pills, modafinil, etc. are a pure waste of time as they keep fighting the inevitable: a misalignment between the work time and the subjective night period. This misalignment can only be remedied by a gradual properly timed phase-shift-based adjustment. Even though many shift workers will disagree with me (mostly for psychological and convenience reasons), I insist that it should be easier and healthier to maintain a night shift for a longer period (e.g. a month) than to do regular cycling between night and day without the body clock having any chance for adjustment. Some cancer researchers also oppose long periods on night shifts due to the documented decline in melatonin that is believed to have cancer protective properties[18][19]. However, those need to be weighted up against an even more serious problem of the circadian disruption.

Excessive sleeping

One of the most persistent myths about sleep is that our body is programmed to get as much sleep as possible. Even some reputable researchers subscribe to this idea! They compare sleep to overeating. Some note how long Inuit sleep in winter. Others note that people allowed to sleep freely often binge heavily and clock up an indecent number of sleeping hours. As if conservation of energy was the main function of sleep. As if all animals were made as lazy as they are perpetually hungry. Some scientists even contemplate sleep restriction analogous to calorie restriction. It is conceivable that sleep restriction might be helpful in some rare cases in sick people (e.g. "wake up to get your medicine"). However, it's analogy to calorie restriction is as weak as the reverse proposal: wake restriction. The myth was probably born from epidemiological studies that show that people who sleep 7 hours per night live longer than those who sleep 9 hours per night. However, the suggestion to restrict sleep to live longer is as smart as an effort to shrink or stretch people just because those who are very short or very tall do not live as long as an average man in the street. We can't demonstrate any evolutionary advantage to getting more sleep than neurally necessary. The harmful myth of excessive sleeping might make you think that free-running sleep will make you sleep longer in the same way as free access to the kitchen will make you overeat. Considering the known functions of sleep, there is no specific benefit to sleeping beyond the standard 6-8 hours. Sleep is a neurophysiological consumer of benefits accumulated in waking (such as learning, exercise, etc.). Its healthy homeostatic and circadian control roughly ensures the optimum proportion of sleep to waking. People who binge on sleep in free-running conditions usually come from a period of long-lasting sleep deprivation or initiate sleep too early in reference to their circadian phase. Their total sleep time quickly drops to their natural average after a couple of days on a free schedule. A study showed that to get over 8 hours of uninterrupted sleep, the sleep should be initiated some 6 hours before the temperature nadir (shortly after the alertness acrophase)(Dijik and Lockley 2002[20]). The same can be seen in SleepChart data submissions. For example, in the presented graph, the maximum length of sleep is obtained when sleep is initiated 3 hours ahead of the most favored bedtime (merely an hour after the evening "forbidden sleep zone"). Those observations have put paid to the idea that we have a tendency to sleep excessively.

Circadian graph that shows that "excessive sleeping" occurs when sleep is initiated too early. In the graph, sleep initiated in the 16th hour is longer than average, while the sleep-wake cycle does not add up to 24 hours (unbalanced cycle with phase advance). In contrast, sleep initiated in the preferred 19th hour is nearly an hour shorter and produces a perfectly balanced 24-hour sleep-wake cycle.

If your main concern is time, you can survive on less sleep and get more time at the cost of your mental acuity. If your main concern is the brain power, you should live by the motto: Maximum efficiency of sleep is accomplished when sleeping without artificial sleep regulation (i.e. without alarm clocks, pills, designer schedules, substances, etc.). Free-running sleep schedule will make you sleep less on average. It will make you sleep much less than on any artificial sleep schedule that forces you to catch up with the accumulated sleep debt. Irregular schedule is bound to produce deficits because you can accomplish irregular sleep only by interfering with it. To read more about excessive sleeping see: Jim Horne and Daniel Kripke.

Sleep habits

In this section, I would like to demonstrate that people can differ vastly in their sleeping habits, and some of the differences have an important underlying biological cause. Scientists use the term chronotype to differentiate between different sleeping time and duration preferences that characterize different individuals. One person's chronotype might make him a short sleeper. Another's chronotype will make him an owl. Yet another's chronotype will make his doctor diagnose a sleep phase disorder. Despite a seeming variety, a small set of underlying variables should make it rather easy for you to figure out your own chronotype. Your chronotype may determine your suitability for certain professions. Luckily, you do not need to determine your chronotype before you choose your major or your job. Many people naturally gravitate towards activities and professions that match their natural sleep habits. A physician or a fireman needs to tolerate shift work and interrupted sleep. Milkmen get up early, while gym or disco owners need to stay up late, while a writer may be of any chronotype as he/she can adapt his/her writing hours to his/her sleep patterns. To illustrate individual sleep patterns I use a freeware application called SleepChart that you can download here to visually chart your own sleep (Wozniak et al. 2003[21]). If you collect a few months of data, I would be very happy to receive your data file for analysis and future research. Sending SleepChart data requires a single click in the program.

Body clock

The cycle of sleep and waking is regulated by the body clock. Body clock is located in the brain and is primarily based in the suprachiasmatic nucleus (see the chapter devoted to the SCN). The clock has a period of about 24 hours. During a single 24 hour day we have a period of 5-10 hours when we are very sleepy. This is the time when we normally sleep. During the remaining 14-19 hours we are usually awake or take a nap at siesta time. As mentioned earlier, only a small portion of the waking time is suitable for top-quality intellectual effort (see: Optimizing the timing of brainwork). The period of maximum alertness may last as little as 2-4 hours. We should plan our day in such a way so that sleep comes at the time of maximum sleepiness, while activities that demand maximum focus or creativity fall into the hours of maximum alertness. It is very difficult and usually very unhealthy to force the body and the body clock to change the timing of waking activities and sleep. It is far easier to do the opposite: adapt one's life to the natural cycle governed by the body clock. That adaptation will depend on the unique properties of one's own body clock. In the following sections I will try to show different types of sleep habits determined by the properties of the body clock that characterize a given individual.

Components of sleep in phase disorders

There are two main mechanisms that regulate sleepiness (see: Two components of sleep). One is the body clock, and the other is the "wake-meter". Body clock produces increased sleepiness every 24 hours. The wake-meter increases sleepiness with prolonged wakefulness (i.e. the longer we do not sleep, the sleepier we are). In sleep literature, these two mechanisms are called the circadian and homeostatic components of sleep propensity. Sleep control components:

circadian clock - circadian clock produces sleepiness in 24 hour cycles homeostatic control - wake-meter measures the period in which we stay awake and triggers sleepiness after we stay up for long enough

In people affected by DSPS or ASPS, there may exist a combination of several factors that make it harder to get good sleep in normal hours:

Circadian clock runs in periods far different from 24 hours. For example, in DSPS people, the circadian clock may be set to 25-26 hours. Circadian clock is not sensitive to time resetting factors (termed zeitgebers). Normal people reset their clock in the morning by light and activity. In addition, darkness and inactivity in the evening provide further clues for the clock. Normal people with normal lifestyles can easily synchronize their sleep with the day-night cycle. Homeostatic wake-meter has an unusual time constant. Sensitive wake-meters will make people get tired very quickly after awakening. Insensitive wake-meter may make people tend to stay up for long. Caffeine abuse could contribute to a fast decline in alertness via adenosine receptor downregulation. Lifestyle has a dramatic effect on the behavior of the circadian and homeostatic sleep regulation mechanisms. The same individual will show a different sleep pattern depending on such factors as: using artificial lighting, exercise, level of stress, timing of exciting activities, napping, diet, climate, changes in ambient temperature, health status, etc.

Lark-owl misconception

Research shows that 15% of people would classify themselves as "morning type" or lark. Another 20% would call themselves "evening type" or owl. The remaining 65% are indifferent or "mid-range". What is your type? You can find many lark-or-owl tests on the net. However, I have not yet seen even one that would be well-designed to truly answer the question of your genetic predispositions. In particular, the same person on a work-week schedule may be classified as a different chronotype than when he or she is on a free running schedule. Few people know that they can easily adapt to a completely different schedule by means of chronotherapy (e.g. by shifting their sleeping hours by 30-45 minutes per day). If you ask a typical owl to go to sleep 30-45 minutes later each day, the owl will keep shifting its bedtime to later hours. Initially, it will sleep during the day. That sleep will shift gradually to even later hours until the owl finds itself going to sleep in the very early evening just to get up before the larks! Surprisingly, even the most committed owl can then comfortably stick to the early waking hours for quite long! There is little natural preference as to the sleeping time of the day! However, there is a factor that drives people into believing they are of a given sleep-time preference type. This is the length of the circadian cycle and their ability to entrain it to 24 hours. As mentioned earlier, typical circadian clock period lasts longer than 24 hours. Those people whose cycle is particularly long tend to go to sleep later each day. They push the limit of morning hours up to the point when their compulsory wake-up time results in unbearable sleepiness. In other words, people with long cycles will tend to work during the night and sleep in the morning as long as it is only possible.

Larks and owls do not differ in their preferred timing of sleep in reference to daytime! The difference comes from the length of the circadian cycle, sensitivity to zeitgebers, and lifestyle. You can easily make a lark work comfortably late into the night and make an owl get up at 3 am. This can be done by chronotherapy (cycle adjustment)! Moreover, owls can keep getting up at dawn if they adopt an ancient farmer's lifestyle (e.g. by giving up electricity).

A smaller proportion of people will experience short circadian periods and experience extreme sleepiness in the early evening. This is the lark type. Life forces larks to go to sleep slightly later than their natural preference (family, work, light, etc.). This keeps larks in line with time and they will often claim that the quiet of the morning, the singing of birds or the beauty of the sunrise keeps them getting up early. Yet it is still possible to forcibly push a lark to gradually shift sleeping hours and behave like an owl! In a modern society, only a small fraction of people can boast a perfectly steady and regular natural sleep pattern. Not only are these the healthiest people around, they are also creatures of habit in reference to their sleep and waking rituals. They obey their rituals religiously, avoid alarm clocks, avoid evening entertainment, avoid medication that affects sleep, etc. Unlike those well-regulated individuals, owls shifted to a morning schedule will gradually tend to advance to their standard late-night rhythm. Similarly, larks will quickly shift back to getting up with the birds. Some correlation studies showed that owls (as defined by the timing of melatonin release) exhibit slightly higher IQs than larks (Roberts and Kyllonen 1999[22]).

Charting sleep with SleepChart

Understanding the control mechanisms that produce sleep and wakefulness is extremely helpful in understanding sleep habits. It is particularly useful in individuals suffering from a number of sleep disorders, esp. insomnia and phase-shift disorders. Simple measurements of circadian variables and simple tools of chronotherapy may bring sound sleep to those who often struggled for years with insomnia, unsatisfying sleep, or sleep in wrong hours. Better understanding of chronobiology could also help extinguish dangerous practices such as poorly planned shift-work, disrespect for health consequences of the jet lag, cumulative sleep deprivation and the Internet fad of Uberman sleep. To illustrate various sleep habits I use charts from a freeware program SleepChart. You can download SleepChart here and begin your own analyses today. All you need to do in the program is to click the beginning and the end of the sleep block in the graph. See the bottom of the SleepChart window for exact time corresponding with the position of the mouse pointer. If you set a wrong block, select it with a click and press Del. Using SleepChart data, I will try to explain the main reason for which healthy people may not be getting refreshing sleep: sleep phase problems. SleepChart attempts to approximate the circadian acrophase that correlates with maximum sleepiness, low body temperature, low ACTH, high melatonin, etc. The underlying assumption is that when you log your sleep with SleepChart, you do not attempt to artificially play with the sleep hours. Each intervention in the sleep schedule makes the tools used in SleepChart work with lesser accuracy. Here are the most important interventions that should be avoided:

waking up with an alarm clock, combating sleepiness in the evening (e.g. in order to delay sleep), and controlling sleep with substances (e.g. alcohol, sleeping pills, etc.).

On those rare occasions when you delay sleep or use an alarm clock, you can disqualify the sleep episode with the appropriate markings. However, all attempts to modify the sleep schedule will partly fool the algorithm and your reading will be inaccurate or plain wrong. It is also very important that you do not attempt to follow the circadian approximation when determining your optimum sleeping hours! You should always give priority to your natural body signals, i.e. sleepiness. Following SleepChart approximations can result in a positive feedback of error. In other words, errors in the graph may be amplified by your attempts to follow the graph. This can disrupt the sleep cycle. At worst, you could even self-diagnose yourself with DSPS without actually suffering from the disorder! Your only and sole "go to sleep" criterion should be rapidly increasing sleepiness. You may use the graph to approximate the moment in which the readiness for sleep will occur so that you could "cool down" in time. You can also find SleepChart helpful in chronotherapy for ASPS or DSPS to make it easier to schedule your appointments without conflicting with your natural sleep rhythm. Courtesy of the numerous contributors who sent in their SleepChart data, we can draw a number of interesting conclusions. The most compelling one is probably the confirmation of the hypothesis that we might be facing an epidemic of Delayed Sleep Phase Syndrome (DSPS) in younger generations, esp. among students and people employed in high-tech jobs. The epidemic is a result of an ever-growing discrepancy between the environment in which humans and their primate ancestors evolved over the last several million years, and the environment in which we live today with electric lighting, Internet, computers, TV, rat race, and 24-hour society. The increasing gap between lifestyles and biology leads many to seek radical solutions and take on drastic measures. A quick survey of those who attempted to adapt to an Uberman sleep schedule reveals an interesting truth. Although the idea to squeeze in more waking hours into a day is very appealing, most of the "experimenters" began their interest in polyphasic sleep as a result of troubles with achieving refreshing sleep! Some people reacted with skepticism to the concept of using SleepChart as a sleeping prop: "it is just far too complicated and Ockham's razor needs to do a bit of shaving! Sleep is as natural as breathing air or drinking water and if you have to set up complicated charts and experiments, and utterly eccentric sleep-activity patterns just so as to get some decent shut-eye, then you must have a problem - but one more of a psychological than a physiological nature". It is true that sleep will occur naturally in a natural setting. The trouble begins when we interfere with nature using caffeine, alcohol, nicotine, artificial lighting, 24/7 society, night-time entertainment, etc. SleepChart may seem complex, but it might still be the easiest way to predict the optimum timing of sleep in free-running conditions for people who may have problems with sleeping. SleepChart will only ask you when you go to sleep and when you wake up (naturally). All computational complexity is hidden in the background. The approximation procedure needs no further input from the user and it predicts the circadian acrophase as well as the optimum bedtime. SleepChart can even disentangle homeostatic and circadian components of sleep. Understanding these can also be helpful in planning healthy sleep. I agree that the need to resort to tools such as SleepChart is a sign of troubled times. However, SleepChart has a proven record of helping people understand their seemingly irregular sleep patterns and organizing their sleep. Falling asleep might be natural, but there are many factors that mask sleepiness or magnify it. For people on very irregular sleep schedules this can pose an insurmountable obstacle! People with sleep problems are often little understood by the naturals: "If you work solidly 8 hours a day, have 3 decent meals, have a proper family life, and treat other people as human beings, then in the evening you go to bed happily knocked out and wake up next morning happily refreshed. Surely this is as it always has been for most people throughout history and surely this is how it will always remain". This attitude towards sleep problems is not much different from telling a clinically depressed person: "Pull yourself together", or expect a heroin addict to go cold turkey and instantly return to normal life. A tortured insomniac will only get more upset with himself or herself if (s)he is told that sleepless nights come from "unsolid work", "indecent meals", "improper family life" or treating others "inhumanely". The trouble stems from the clash of biology with modern lifestyle. With the arrival of artificial lighting sleep disorder statistics skyrocketed. These were only made worse by television, computer games and the Internet. With the advent of mobile telephony and instant messaging, insomnia and sleep phase disorders seem to reach epidemic proportions. Fewer people are able to leave work behind, cope with stress, or give up evening activities. Without a major change in lifestyle or a breakthrough in circadian control methods, people affected with lifestyle-related sleep disorders are faced with a choice between a daily sleep deprivation misery and radical solutions such as throwing away the alarm clock. Certainly, we can expect science to come up with answers to the problem. Until that happens though, waking up "happily refreshed" remains a privilege of a shrinking subset of the population in industrialized nations.

SleepChart in SuperMemo To make it possible to analyze the connection between sleep and learning, SleepChart has been integrated with SuperMemo speed-learning software. Instead of explaining SleepChart itself, I will shortly describe its functionality in SuperMemo. Keep in mind that some of the functions related to memory are not included in the freeware version due to the fact that it does not have access to your learning data. SleepChart was included in SuperMemo a few years ago upon the understanding that sleep is vital for learning. To sleep well and to learn well, one needs to understand his or her own circadian rhythm. SleepChart in SuperMemo was designed with the view to assisting in that task. It can help you optimize the timing of sleep as well as to optimize the timing of your learning. Moreover, you can submit your sleep and learning data for analysis and have your own contribution in our research over the impact of sleep on memory. You can access SleepChart in SuperMemo with: (1) Tools : Sleep Chart on the Main menu, (2) SuperMemo commander, or (3) by just pressing F12.

Sleep blocks are marked in blue. Learning blocks are marked in red. Total learning time on individual days is displayed on the right. Selected sleep block is displayed in yellow. The length of that block is displayed at the bottom.

In SuperMemo, the learning timeline is generated automatically. Each time your make repetitions with SuperMemo, the learning block is added to the timeline (displayed in red on the graph). On the other hand, your sleep data must be logged in manually (displayed in blue). At minimum skill level, you can use SleepChart for a basic visual inspection of your favorite learning and sleep hours. However, more advanced functions such as optimizing the time for learning or the time for sleep require advanced analysis and understanding of circadian rhythms. If you start logging your sleep data today, you will be able to use future, more advanced versions of SuperMemo to study and understand your sleep and learning.

Sleep timeline in SleepChart The timeline of sleep in SleepChart must be logged manually. To log a block of sleep, click the beginning of the block (sleep start) and then click the end of the block (sleep end). You can also start from clicking the end of sleep first. Sleep blocks above 22 hours are disallowed. Sleep blocks cannot overlap with repetitions timeline (you cannot learn with SuperMemo and be asleep at the same time). If you have already collected your sleep data in SleepChart Freeware, you can import this data to SuperMemo with File : Import : SleepChart file (you can also import data from a spreadsheet). If you import files from SleepChart Freeware, you can test for sleep and learning overlaps with File : Verify : Block overlaps. Protection from block overlaps is an important advantage of using SleepChart in SuperMemo as opposed to a standalone SleepChart, in which it was very easy to fall out of phase in logging data (e.g. by failing to fill out a single day and noticing that only a month later). You can mark blocks of forcefully delayed sleep, as well as mark blocks cut short with an alarm clock or other factors. Please note that you can get best analytical results if you do not artificially regulate sleep (e.g. with an alarm clock, sleeping pills, etc.). Applied models will not fully account for artificial intervention. Last but not least, natural sleep is what you should aim for in learning as well as for the sake of maximum health and well-being.

Sleep and learning timeline in SuperMemo Combining sleep timeline with repetition data taken from SuperMemo opens an array of new research and optimization options. Various sleep statistics pertaining to individual days can be displayed on the right. Sleep blocks can be consolidated with the Consolidate button on the toolbar. For example, if you woke up for 5-10 min. in the night, consolidation will make SuperMemo treat the entire night sleep episode as a single entity. Short nocturnal awakenings are a norm, even if we are not aware of them, and have little impact on learning. Sleep block consolidation often unmasks important properties of sleep (e.g. see Preference for night sleep). It helps treat successive sleep episodes as an expression of a single period of high sleep propensity. In addition to sleep statistics, optimum bedtime can also be estimated in SleepChart. Two independent models are used to predict middle-of-the-night points as well as the expected optimum retirement and awakening times. Those approximations may be helpful in optimizing sleep in people who work shifts or sleep in irregular hours for various reasons. For example, after a week of irregular sleep, it may be difficult to determine the optimum retirement hour that is likely to produce best quality sleep. Going to sleep too early might result in premature awakening (which may often ruin the night sleep entirely). Going to sleep too late may result in short night sleep, sleep deprivation, and reduced alertness on the following day. Predicting optimum sleep time on the basis of sleep history is inexact science, and the two models used may produce different outcomes. Important! Your natural instinct should always take precedence over mathematical models. Moreover, best results in sleep optimization are accomplished in free-running sleep. If you use an alarm clock, or force yourself awake through the night, or take sleeping pills, the models may not adequately account for the chaotic change that is occurring in your sleep control systems.

Blue and red continuous lines are predictions of optimum sleep time using the SleepChart model (based on sleep statistics). Yellow continuous line shows the prediction of the maximum of circadian sleepiness (circadian middle-of-the-night peak) using a phase response curve model. Note that theoretically, yellow line should roughly fall into the middle between blue and red lines. However, when a disruption of the sleep pattern is severe, those lines might diverge testifying to the fact that it is very hard to build models that fully match the chaotic behavior of the sleep control system subjected to a major perturbation. Aqua dots point to the predicted daytime dip in alertness (i.e. the time when a nap might be most productive).

Circadian graph The circadian graph in SleepChart can help you better understand your sleep patterns, as well as to visualize the degree of cycle instability (i.e. how difficult it is for your sleep-wake cycle to fit into 24 hours). You will need a few months of data before the graph becomes meaningful. In addition, subjective night approximation lines in the sleep log are subject to substantial hysteresis. If your lifestyle changes dramatically (e.g. as a result of a therapy), you may need a few weeks for the approximation lines to align properly with data. The circadian graph may then be more difficult to interpret. In such cases, you can use From the first day and To the last day options to demarcate the period of interest. This will limit the analysis to a selected period characterized by a selected lifestyle.

Exemplary circadian graph of a monophasic sleeper

Sleep initiation Blue line shows the preferred time to fall asleep. It corresponds with sleep propensity derived from the number of sleep blocks falling into a given hour of the waking day, where zero on the horizontal axis refers to the hour of waking up. Percentage of sleep episodes initiated at any given time is displayed on the right vertical axis. The blue line roughly expresses your "tiredness of wakefulness". It also expresses your ability to fall asleep. Your own optimum bedtime hour is your personal characteristic as it differs between people. For most people the optimum bedtime falls into the range of 16-20 hours from waking. In the example, the most favored bed time occurs in the 18th hour of waking.

Sleep maintenance Red line shows the average length of sleep. This line is a rough reflection of the ability to maintain sleep, i.e. the longest sleep episodes occur during the subjective night. The average length of sleep is displayed on the left vertical axis. The graph will tell you that even if you are able to initiate sleep during the day, it will never last long. In most cases of regular sleepers, only after 11-14 hours of waking does the length of initiated sleep start increasing. Note that the sleep length graph is slightly phase shifted in reference to the preferred sleep initiation time due to the fact that long sleep is mostly achieved by initiating sleep early.

Optimizing bedtime If you are trying to determine your optimum bedtime, find the evening peak in the blue curve and choose nearby points that produce sufficiently long sleep (red curve high enough). In addition, pay attention to the fact that your wake and sleep time should add up to 24 hours, otherwise you will experience phase shifts. Some people take naps during the day. Others don't. In nappers, the blue curve should also point to the maximum mid-day alertness dip. Short nap time may actually be a sign of good nap timing as long as the nap is not taken too early in reference to the blue curve (see: Best nap timing). Non-nappers will also experience a peak of sleepiness around the 7th hour even though their blue curve will not show as a prominent bulge. If the graph shows that your optimum nap time falls into the 8th hour, and you wake up at 6 am, you should take a break at around 14:00 (2 pm) and look for a secluded place for a few minutes of rest. You could also plan your lunch at around 13:00-13:30 to complete a perfect setting for a siesta.

Example 1: Unstable circadian cycle In the exemplary circadian graph below, on average, the best night time sleep is obtained when it is initiated after 18 hours from the morning awakening (assuming the graph was created without any artificial form of sleep control such as an alarm clock, delaying sleep, etc.). The blue line shows that the 18th hour is the preferred time to initiate sleep, while the length of sleep (red line) is long enough to add up to a 24 hour sleep-wake cycle.

As blue peaks are of the same height, we can conclude that the graph represents a religious napper, whose optimum siesta time occurs 7 hours from awakening. In this case, for an awakening at 8 am, the siesta should begin at 3 pm, and the night sleep around 2 am. For both blue peaks, 7.4% of all sleep episodes being at the optimum hour, while the remaining 85% are suboptimum. Maximum length of sleep can be achieved at the 16th hour, however, this does not indicate this is the optimum hour of going to sleep. If sleep is initiated too early, it may or may not catch on the full circadian low of the subjective night. In other words, there is a risk of a premature awakening after just a couple of minutes of sleep. Such an awakening makes it harder to fall asleep again. This is one of chief causes of insomnia. The difficulty in re-initiating sleep is due to a very rapid loss of homeostatic sleep propensity during sleep. In addition, sleep initiated before the full circadian low does not seem to be of more value than slightly shorter sleep initiated a bit later (e.g. as reflected by the subjective feeling of being refreshed in the morning, or as measured polysomnographically). The blue homeostatic line indicates that the sleep is more likely to be initiated effectively at the 18th hour, while its average length is then 6 hours. If your graph is generated without attempts to artificially regulate sleep, the second peak in the homeostatic curve will often indicate the optimum bedtime. The graph also indicates that if the sleep is delayed by an hour, it will be shortened by 10-30 minutes. It is possible, that even this little shortening will affect the performance during the day. If the sleep is advanced by an hour, it may be 10-30 minutes longer but its quality is not likely to increase proportionally. The graph can also show how the length of the circadian period can be determined by the bedtime hour. The green line shows the set of breakeven points for a stable 24 hours sleep-wake cycle where the sleep and wake times add up to 24 hours. All the circadian graph points that lie to the right of the green line cause a phase delay, while points on the other side will cause a phase advance. Aqua blue line shows where the 24-hour-cycle green line crosses the red sleep length line. Due to the fact that the angle between green and red lines is large, this sleep pattern is pretty unstable. This means that going to sleep before the 18th hour will result in a cycle that is less than 24 hours long, while going to sleep after the 18th hour may lengthen the cycle and result in phase shift delays. For example, early bedtime (around the 15th hour) will result in a day that lasts 21 hours (15 hours on the horizontal axis corresponds with the average sleep length of 6 hours read from the red curve). Later bedtime (around the 18th hour) will result in a perfect 24 hours day, while a very long waking day (e.g. 20 hours) will produce a day lasting 25.5 hours. Naturally, all manipulations in the length of the day would better be avoided as early bedtime increases the chances of insomnia, while a very late bedtime increases the chances of sleep deprivation, and REM sleep deficit. Understanding one's sleep preferences can be very helpful for planning shift-work or combating jetlag in long-haul flights.

Example 2: Stable circadian cycle The second graph shows a sleep pattern that is much more stable that the one from the first example above.

The graph shows a habitual napper who shows a preference for a waking day of 19 hours. As opposed to the graph shown earlier, the zone of stable sleep-wake cycle, demarcated by vertical aqua lines is much wider due to the fact that red and green lines are nearly parallel. This means that if the sleep is initiated after the 20th hour of waking, the night sleep will be shortened to fit the 24h cycle. Naturally, even if delayed sleep does not cause a phase shift, it will always result in lesser sleep quality due to stage compression. Such sleep will result in sleep deficits. Days lasting less than 20 hours may result in a phase advance. Despite running free, the longest average sleep period (initiated at around the 16th hour) isn't even 6 hours long. This illustrates that excessive sleeping is not a problem in free running sleep. In the graph, the optimum siesta time again falls in the 7th hour and is executed religiously (over 14% of sleep episodes executed "on the dot").

Phase shift disorders As shown in both graphs above, with sufficient discipline, people with phase disorders should be able to accomplish 24 hour free running rhythm independent of the desired waking hour. In practice, due to various perturbations in lifestyle (exams, stress, socializing, etc.) as well as due to the stress of the need to wake up early, adherence to the optimum 24h sleep schedule may be very hard to achieve for people with severe phase shift problems. For those who need to wake up at a specific early hour, free running sleep may become unobtainable without the use of an alarm clock, melatonin, or other unwelcome measures.

24-hour sleep cycle

Perfect 24-hour cycle Let us now consider an ideally synchronized 24-hour cycle. In the picture below, an octogenarian female wakes up naturally everyday around 3:00-3:30 am. She sleeps 5.4-5.5 hours per day, wakes up refreshed and is active throughout the day.

There is no synchronization with daylight as the waking hour falls into the period of darkness. The cycle is synchronized by evening activities, not daylight. The subject keeps in her mind a "must go to sleep" hour estimation that helps synchronize body clock with the time of day. This "psychological imprint" is illustrated by a smooth change in the sleeping rhythm after the end of the daylight saving time on Sunday October 27, 2002 (the graph disregards DST so that the waking hour before the change is set at 2:00-2:30 am). Even though aging is said to increase nocturnal awakening, perhaps due to the cell loss in sleep control centers, this subject reported no awakening in the study period. Circadian graph shows a single favored bedtime in the 19th waking hour. As the average nighttime sleep episode is 5 hours long, the sleep-wake cycle lasts exactly 24 hours, and daily fluctuations in bedtime are minimal. As the green breakeven line and the red circadian line are nearly parallel in the span of 3 hours, this sleep pattern is very stable, and all delays in bedtime occur at the cost of sleep time without causing a phase delay.

Sleep and stress Stress can ruin the fabric of sleep. The following SleepChart graph demonstrates the impact of stress on a well-balanced 24 hour sleep pattern:

In the presented example, a middle-aged self-employed male wakes up naturally everyday around 6:00-6:20. However, on Jun 3, 2003, a severe family problem threw the rhythm into chaos as evidenced by frequent nocturnal awakenings. The rhythm returned to the norm one month later as soon as the family conflict was resolved.

Monophasic sleep Monophasic sleep graphs will often show a small siesta-time sleep propensity peak due to the fact that even the purest monophasic sleeper hits crisis days in which a postprandial nap brings a welcome relief. Due to their "crisis nature", such naps may last longer than in a habitual napper. The mid-day peak is particularly visible in irregular sleepers who show less discipline in sheltering their natural regular sleeping hours.

Preference for night sleep

Independent of the innate circadian cycle, light has a powerful impact on sleep. In particular, its phase-shifting capacity will always ensure that humans naturally gravitate towards sleeping at nighttime. Only the advent of lifestyle that involves electricity and 24h work cycles triggered the present epidemic of sleep disorders, which indirectly contributed to the appeal of concepts like "Uberman sleep". The preference for sleeping in the night can best be seen in irregular sleepers, esp. those who suffer from phase shift disorders and run their sleep free, or those who are on a free running schedule and phase shift "by choice" (i.e. by not trying to fit any particular sleeping hours). In those cases, using the circadian graph in SleepChart, we can see the impact of nighttime on the ability to initiate and maintain sleep. In the presented circadian graph, we see a clear preference for night sleep in free running sleep. The graph shows that sleep initiation (blue line) is easier at nighttime between 7 pm and 4 am, while the length of sleep (red line) is greatest if the sleep is initiated between 10 pm and 5 am.

The graph can also be interpreted as a phase space. It shows how difficult it is to achieve "wasteful" 8 hours of sleep in an efficient free running sleep pattern. It can also be used to demonstrate that no trajectory in the phase space will lead to an entrained polyphasic sleep. When alarm clock and/or sleep delay are introduced into the system, sleep control may become chaotic. However, in free running mode, it quickly stabilizes around a roughly biphasic rhythm, often with a degree of phase-shift dependent on the lifestyle. The timing of phase-shifting, excitatory and inhibitory stimuli, even if they are repetitive and regular, may still lead to a degree of chaos in the system. This occurs if the period of the stimulus cycle is different from the period of the entrained circadian rhythm. In contrast to the first graph, the second example can be used to argue that artificial lighting can virtually eliminate the impact of natural light on the cycle in a well-disciplined sleeper with a more regular cycle and better adherence to free running sleep rules.

The question remains open to whether the nighttime sleep preference isn't to a large degree caused by social entrainment. Despite the fact that we live in a 24/7 society, there is still more fun to be had during the day or in the evening than during the night when still the larger portion of the population is asleep. A big clue comes from the fact that despite little difference in sleep initiation preference throughout the day, sleep initiated in the evening or in the night (8 pm - 6 am) is still likely to last up to twice as long as sleep initiated at 3 pm.

Biphasic nature of human sleep

Most researchers agree that human adult circadian cycle is biphasic. In addition to sleep, one of the outward expressions of the circadian cycle is the changes in core body temperature.

Temperature changes in the course of the day in degrees centigrade (courtesy of: Dr Luiz Menna-Barreto, State University of Campinas, Brazil)

SuperMemo and SleepChart provide an excellent tool to verify the claim of the biphasic nature of human sleep-wake cycles. I have collected data from monophasic and biphasic sleepers that illustrate our biphasic nature.

Biphasic learning SuperMemo alone makes it possible to see the biphasic character of the learning performance throughout the day by charting grades vs. the clock time without the need to include sleep log data. In the presented example, a monophasic sleeper, a busy father of two, shows the best learning performance in the early morning around 6 am, i.e. shortly after his natural waking time. There is a big dip in the average grade scored when learning in hours 11 am to 1 pm (on the clock). There is a second surge in the quality of learning at around 5-6 pm:

Biphasic sleep periodogram SleepChart alone can also be used to demonstrate sleep biphasicity. Free running sleep logs can be subject to Fourier analysis to reveal the nature of sleep periodicity. An exemplary periodogram is shown in the graph:

Exemplary periodogram of human free running sleep reveals a biphasic nature of sleep periodicity. Two basic sleep frequencies dominate this particular sleep log. These roughly correspond to 12 and 24 hour cycles.

Biphasic learning and sleep If we employ both SleepChart and SuperMemo, we can also see how waking performance changes in reference to sleep phase. The biphasic grades graph from SuperMemo (as shown earlier) can be corrected for the circadian phase that can be pretty independent of the actual clock time, esp. in free running sleep. In the presented example, a biphasic sleeper, middle-aged male with irregular sleep patterns, shows the best learning performance in the early morning (roughly around the estimated end of the subjective night):

There is a big dip in the average grade scored some 7 hours from the morning peak. There is a second surge in the quality of learning in the evening. Finally, there is a steep decline in the quality of learning shortly before sleep.

Biphasic graphs in SuperMemo The newest version of SuperMemo makes it possible to correlate recall with the circadian phase as estimated by SleepChart (which has been integrated with the program). In the presented example, a biphasic 45-year-old male shows two major peaks in alertness and learning quality during the day:

The first peak occurs in the hours 3-4 from the estimated natural waking time, i.e. not the actual waking time, which may be different. The second, slightly longer peek spans hours 12-18. There is a pronounced depression in free recall at the 8th hour of the subjective day period (i.e. wake time estimated from the circadian data, not the actual waking period). The red line shows the estimated overall alertness derived from SleepChart's two component model. In this case, the estimated alertness nearly perfectly matches the recall measured during an actual learning process.

Monophasic sleep with biphasic learning The height of the two alertness peaks may differ in a monophasic sleeper, who will also show the same depression in recall around the 8th hour of the subjective waking day. However, characteristically, a monophasic sleeper may not get the same performance boost in the evening as biphasic sleepers due to the effects of the homeostatic sleep drive component. Even a few minute nap can result in a major boost in alertness. This has already been noticed by a prominent napping expert Dr David Dinges in his comprehensive surveys comparing habitual nappers with non-nappers (Dinges 1989[23]). To illustrate the difference between biphasic and monophasic sleepers, see an analogous recall graph in which a monophasic 15-year-old non-napper shows the best performance in the morning hours with a sharp dip at the 8th hour of wakefulness coinciding with a subjective decline in cognitive function:

After a temporary dip, there is a sharp recovery, and a gradual decline in performance in the second half of the day. That decline is strongly accelerated by a homeostatic mechanism. The yellow line shows the estimated circadian component of alertness. In this case, the circadian benefits are muffled by the homeostatic decline in alertness, which is not shown in the graph. This is why the hypothetical circadian alertness and the actual alertness match only in the first half of the day.

Biphasic circadian graph There is a biphasic twist to the two-process model of sleep propensity. In free running sleep, where sleep is a true expression of sleep propensity, it is possible to visualize both the homeostatic and the circadian components of sleep in a circadian graph:

In a habitual napper, the circadian biphasic nature is paradoxically expressed by the two-peak sleep propensity curve instead of the circadian curve. The reason for this role reversal is the physiological difference between the two circadian peaks in sleep propensity. In a habitual napper, sleep is initiated as easily at siesta time as it is initiated at night. However, the length of sleep at siesta time is very short (usually 15-80 min). In the presented graph, the blue line corresponds with the ability to initiate sleep at any given circadian time. On the horizontal axis, it aligns well with the alertness graphs displayed in SuperMemo (as shown in earlier paragraphs). It aligns well with both the learning data, as well as with the two-process sleep model implemented in SleepChart. The red line corresponds with the ability to maintain sleep. It reveals what is not visible in the alertness graph shown earlier: siesta naps cannot last long and will always be subject to an early natural termination (low red line under the first blue peak). In contrast, the period of subjective night is the only time of day when sleep can and should last longest (usually no less than 4-5 hours). The red peak is also the reason why polyphasic sleep adepts crave for "core sleep", wake up groggy, and need heavy alarm artillery to wake up in this critical subjective night period. David Dinges, in his surveys noticed, that napping more than once within a day was extremely rare. Most nappers took naps lasting 15-120 min. Naps will be shorter if they are taken before the siesta peak. If they are taken after the peak, they will usually last longer, and may even integrate with the night sleep in cases of particularly large delay, or where there is a sleep deprivation, REM-sleep deficit, or any other form of "sleep debt". Dinges noticed that both appetitive (habitual) and replacement (compensatory) nappers tended to time their naps 7-8 hours from waking (see: Best timing of naps). Even though napping habits may differ, the circadian timing of the siesta trough seems to be pretty similar across the population (Dinges 1992[24]) It is important to note again that the evening boost in alertness is magnified by a nap, but shows up also in non-nappers and can easily be deconvoluted in the two-processes model into its homeostatic and circadian components (as shown in the next two examples).

Two components of biphasic sleep propensity The last two graphs show the impact of the circadian and homeostatic components on alertness. In the first example, a free running female 29-year-old non-napper shows an alertness dip in 8-9 hours since waking. The red homeostatic estimate shows no dip and a steady decline over the waking day:

The yellow circadian estimate shows the expected position of the dip and the evening crest that explains a boost in the evening learning performance:

Both the evening recall boost and the evening circadian estimate align pretty well showing once again that the overall alertness depends on both homeostatic and circadian components of the sleep control system.

Biphasic performance in sleep deprivation Mid-day slump is as prominent in conditions of severe as well as mild sleep deprivation. This graph shows a mid-day alertness slump in a 26 hour sleep deprivation study (Czeisler et al. 2006[25]). The timing of the slump (hours 10-12 of waking period) indicates that the preceding sleep episode was positioned suboptimally (hence the need to interrupt sleep for the study). Natural awaking would probably take place 1-2 hours after a forced awakening in lab conditions. The graph also shows that sleep inertia caused by forced awakening from Stage 2 NREM or REM sleep causes a much greater cognitive decline than 26 hours of sleep deprivation.

Summary: Napping is good!

Humans are biphasic in nature and show a circadian boost in learning in subjective evening hours.
Non-nappers show a mid-day dip in performance and might also benefit from a siesta.

Segmented sleep

In 1992, Dr Thomas Wehr published the results of his interesting experiment on sleep in periods of prolonged darkness (e.g. as seen in Inuit during the arctic winter)(Wehr 1992[26]). He divided the experimental day into 10 hours of daylight (photoperiod) and 14 hours of darkness (scotoperiod). This type of artificially controlled environment resulted in segmented sleep that was often composed of two 4-5 hour segments separated by an hour of wakefulness. Wehr found that the onset of sleep was associated with an increase in melatonin, which is released in the periods of darkness (in both diurnal and nocturnal animals). He also noticed that the release period of nocturnal melatonin lasts longer in shorter photoperiods (Wehr et al. 1993[27]).

Fragment of a segmented sleep log produced in conditions of 10 hour photoperiod.

Interpretation of segmented sleep When the results of the experiment were publicized, insomniacs rejoiced: Perhaps this is normal? Perhaps this is how we all should sleep? Those who tend to wake up in the night and spend an hour or so reading, watching TV or plundering the fridge, no longer had to feel abnormal. Indeed, the best criterion that should separate healthy sleep form unhealthy patterns is the refreshing power of sleep. Nocturnal awakenings should not matter as long as they did not contribute to morning misery. A historian, Dr Roger Ekirch noticed that this prolonged two-part sleep is frequently mentioned in historical records that predate the advent of electricity: "Until the close of the early modern era, Western Europeans on most evenings experienced two major intervals of sleep bridged by up to an hour or more of quiet wakefulness. [...] The initial interval of slumber was usually referred to as "first sleep," or, less often, "first nap" or "dead sleep." (Ekirch 2001[28]). Sleep researchers speculated that this is perhaps how healthy sleep should look like and that our sleep control models with a single nighttime circadian peak are wrong. Evolutionists speculated that this could be an adaptation to nighttime sex, or breastfeeding, or periods of extra vigilance. Dr Horne likes to refer to segmented sleep as an example of the human propensity to excessive sleeping.

Segmented sleep and Borbely model I happen to disagree with most of the interpretations put forward thus far except those that stand in agreement with the mainstream sleep research. We need to observe that most of human and pre-human evolution took place in tropical areas with far shorter nights than those that characterize winters in the north, and, mathematically speaking, there should be no preference for waking up in the middle of the night for 1-2 hour as opposed to entering shallow sleep or waking at the end of each full NREM-REM cycle. The segmented sleep observed in Wehr's experiment can easily be accounted for with Borbély model of sleep. Even though Borbely model provides very specific mathematical conditions needed for initiating sleep, we must remember that it is only an approximation of reality that does not necessarily account for the level of lighting or external arousing stimuli. In periods of prolonged darkness and silence, lesser overall sleep propensity will be needed to initiate sleep. I will try to illustrate my claim using SleepChart's two-component model and some real life examples.

Segmented sleep and two-component model When Wehr's data are processed using SleepChart's two-component model, we see that sleep is characteristically initiated at periods of relatively low sleep propensity:

Wehr's segmented sleep as interpreted with the help of the two-component model of sleep employed in SleepChart.

In real life, the two-component model indicates that sleep is initiated when alertness levels drop to 33-40%. In segmented sleep, alertness at sleep onset is much higher: 40-50%. Circadian graph shows that the favorite sleep initiation hour is the 15th from arising and it results in 5 hours of sleep on average. As waking comes close to the circadian acrophase, wakefulness cannot last long due to a rapidly ascending circadian sleepiness. The second bout of sleep then follows in the 21st hour and lasts 3 hours on average. Thus the sleep is segmented into a 5 hour long pre-sleep and 3 hour long "correction".

Circadian graph based on Wehr's data.

Sleep periodogram shows a typical frequency peak at period 24h, and two atypical peaks at 8 and 6 hours (instead of the usual 12h siesta peak).

Periodogram based on Wehr's data.

Examples of segmented sleep I scanned years of sleep logs in search for natural segmented sleep examples. I did not found that many. Without doubt, I can blame the modern lifestyle that rarely permits a leisurely early bedtime. Below I list three very different examples from real-life logs. Several characteristics seem to be associated with segmented sleep:

this sleep often results in high alertness, e.g. as testified by the absence of daytime napping as predicted, this sleep is easier to find in winter periods intense exercise may be a factor that helps induce segmented sleep (perhaps due to earlier bedtimes) as in Wehr's data, SleepChart's two-component model of sleep propensity shows a very rapid decline in sleep propensity early in segmented sleep due to the fact that the sleep is initiated very early in reference to the circadian acrophase

Example: Premature bedtime Typical long darkness premature bedtime segmented sleep. Sleep initiated too early, again with a very marked decline in sleep propensity resulting in a nocturnal awakening:

Example: Nocturnal awakening caused by stress Premature awakening caused by stress. Segmented night with a "correction":

Example: Intense exercise Prolonged sleep induced by intense exercise with increased demand for sleep. Over 12 hours of segmented sleep are initiated early with multiple harmless awakenings, fast decline in sleep propensity (inverse of the red line) in the first 3-4 hours of sleep that results in shallow prolonged sleep:

Application of segmented sleep This type of sleep results in very refreshing nights, however, it would be pretty hard to implement in agreement with the modern lifestyle. Certainly, it would not optimize the time use. I can only guess that matching sleep well with the circadian acrophase should also increase the efficiency of sleep. This should be verifiable with SuperMemo data, however, as of the moment of writing, I have not done the necessary computation. Considering the nice effect of this ancient sleep on mood and alertness, I would love to subject myself to an experiment with 14 hours of darkness, however, 10 hour working day would be pretty hard to stomach even in a short term. I also doubt I would be able to extinguish the thoughts of the day and initiate sleep early. Even the mere fact of collecting exciting data for the experiment would keep me up with my thoughts racing. I might try this in retirement when my vital powers decline sufficiently enough to make it truly enjoyable.

Delayed Sleep Phase Syndrome (DSPS)

When a tendency to go to sleep later each day is strongly pronounced, it may become a serious problem. People with a particularly long circadian cycle or with an insufficient sensitivity to zeitgebers are classified as suffering from Delayed Sleep Phase Syndrome (DSPS for short). Sometimes the abbreviation DSPD is used where syndrome is replaced with disorder. The terms non 24-hour sleep/wake syndrome (N24, N-24, Non-24) or hypernychthemeral syndrome (with a few spelling variants) are occasionally used to refer to the most severe cases. I will consistently stick with the label DSPS to emphasize that these are all variants of the same problem expressed differently in different circumstances. This quarrels with the established definitions used by other authors, which I will disrespectfully ignore due to the fact that the established terminology leads to a harmful confusion and the sense of disabling inevitability. In DSPS, an individual finds it difficult to fall asleep late in the night, and sleeps well into the afternoon if not awakened. DSPS has only been characterized in 1982, but increasing data indicates that various degrees of DSPS occur with epidemic frequency, esp. among high school and university students. DSPS individuals often like to keep on learning late into the night, go to sleep very late (for example, 4-6 am), and find it very hard to wake up early on a regular basis. For example, regular getting up at 7 am is a pure torture for individuals affected with DSPS. They often fail to keep jobs that require them to perform early in the morning. Very often, they tend to split the day sleep into two components. For example, DSPS students often get a short sleep in the night, wake up early with an alarm clock, go to school where they are semi-conscious and perform poorly, get a solid nap after school and only late in the evening they regain vigor and their full mental powers. DSPS students feel best after midnight when everyone else is asleep and they can focus on learning or other activities (reading, Internet, watching TV, computer games, etc.). The main factors contributing to DSPS:

increased period of the body clock (well above 25 hours) reduced or increased sensitivity to factors that reset or advance body clock (e.g. light, activity, stress, exercise, etc.) electric lighting, 24-hour economy and the resulting "want to do more" lifestyle

A normal individual has a body clock running with a period slightly longer than 24 hours. The clock is reset in the morning with activity and bright light. Thus a normal individual easily adjusts to the standard day-night cycle. However, DSPS individuals may have their clocks running periods long enough to find it hard to fit to 24 hours. They also push their clocks ahead by activity late in the evening (the process opposite to the morning reset synchronization). DSPS individuals, when given a chance to sleep when they want, will tend to go to sleep later and later. They will also wake up later and later. DSPS people do not have problems with sleep if they sleep in their favorite hours. Most mild DSPS cases can be remedied by changes in lifestyle, but rarely are those changes painless to individuals affected by the condition. If this description fits your problem, you may diagnose the degree of your DSPS with SleepChart freeware.

DSPS in teenagers Research shows that DSPS is very frequent in adolescence (Carskadon 1995[29]). Teenagers with DSPS will often find it difficult to adapt to normal school time. They will experience maximum daytime sleepiness at 10 am (in the middle of the school day) and a peak in alertness right after the school. For many teenagers with a natural tendency to go to sleep late, school becomes a torture and a true waste of time! Educators have already taken on this subject; however, students dozing off during classes are still a norm! Sleepy students learn little, and may naturally develop strong negative feelings for the school in general. This is a problem of colossal proportions! If you are a parent of a teenager who finds it difficult to wake up for school, you will need to act now! Otherwise young man's school years will be a period of monumentally wasted time! It won't be enough to demand an early hour for going to bed. If you ban the late evening Internet surfing, you will just swap a dose of evening education for an idle tossing and turning in bed. Actually, there is only one simple solution, let the kids get up at their natural time but... this may not be realistic in most cases. Your sleep therapist may not be able to help either. The whole school system might need to be changed to accommodate the prevalence of DSPS among adolescents. There have been positive results noted in schools that decided to start classes 1-2 hours later. However, long circadian cycles may result in students staying up yet later in the long-run. Researchers suggest schedule stabilization and gradual realignment. Those measures may still be largely ineffective. Homeschooling and free running sleep could be a great option for those kids.

Solution to the DSPS problem Free running sleep is usually an instant solution to sleep problems in DSPS, however, it inevitably results in a "shifting" sleep pattern (see below). Other than free running sleep, the best known remedy is to:

cycle the sleep phase to alignment with the desired hour bracket and battle to reset the cycle (see: Curing DSPS and insomnia)

In other words, if possible, you could use your natural tendency to go to sleep 1-2 hours later, until you align with the desired sleep rhythm. At that point, the real battle begins by efforts to provide strong morning resetting stimuli (e.g. bright light, stress, exhaustive exercise, etc.). Those can be enhanced by evening measures such as melatonin and the avoidance of phase delaying factors such as light, stimulation, stress, Internet, etc. In general, you need to provide resetting stimuli in the morning, and avoid evening delay factors such as computers, TV, artificial lighting, etc. For most people, a degree of sleep deprivation is more acceptable than several futile inactive hours in the evening in a dark room.

Is DSPS a disease? Probably, most of the cases of DSPS can be explained by a lack of compatibility between the genetically determined sleep control system and the lifestyle. For some people, the degree of the problem may be greater than for others (see: Clock Genes and mutations affecting the clock period (Golombek and Rosenstein 2010[30])). Everyone can easily cure the disorder with a decision to drastically change one's habits (e.g. a return to a farmer's lifestyle). However, such a change is usually not feasible due to the type of employment or family life conditions. This means that DSPS sufferers are probably, for a while, sentenced to wage a constant battle with their body clock. Officially, 0.2% of adults suffer from DSPS. Using numerous SleepChart data submissions, I see a true epidemic of DSPS. Moreover, there is a large hidden DSPS population. I have seen cases where people started showing DSPS sleep patterns as soon as they gave up an alarm clock after years on a normal schedule with a seemingly normal life contaminated somewhat with a degree of sleep deprivation. Admittedly, people who write to me are already a pre-selected population, but the numbers are really staggering. I am pretty sure that most of those DSPS cases are lifestyle related. As the term "syndrome" might suggest DSPS is a disease, I keep emphasizing that DSPS is rather a reflection of our modern electricity-based lifestyle than an actual disorder. Interestingly, I received very few ASPS submissions. It seems that it is DSPS people that hang out late in the night googling on their PC for solutions to their sleep problem. In the end, they arrive to SleepChart and the concept of free running sleep that can be their magic cure (if ever truly affordable). DSPS epidemic can be considered a civilizational disorder in which the pressure of a modern lifestyle stands in disagreement with millions of years of evolution. In the long run, once we fully understand all biochemical and hormonal processes underlying sleep, it is possible that mild pharmacological intervention will make it possible to regulate the circadian cycle.

Asynchronous DSPS Combating phase shift People suffering from DSPS find it difficult to synchronize with the 24-hour clock. In the picture below, an adolescent female with a mild DSPS suffers disintegration of the sleeping rhythm due to the failed efforts to synchronize with "the rest of the world":

After the vacation period, she begins in early September well-synchronized with the "rest of the world". She wakes up between 6:30 and 10:00. However, her body clock experiences continuous shift in her subjective night period. Soon she wakes up at 12:00 and begins a struggle against the further shift. This results in the disintegration of the sleep cycle, short sleep periods below her preferred average (e.g. 4 hours) and frequent bouts of tiredness. SleepChart attempts to plot the extent of the subjective night (i.e. the hours of maximum natural sleepiness). The statistically predicted subjective night is bracketed between the red and blue lines. Circadian acrophase (middle-of-the-night) is plotted in yellow. Circadian sleep propensity is expressed by the shades of red. Sleep blocks terminated with an alarm clock are marked in aqua. Clearly, the greatest disruption in the sleep pattern occurs at the point where the "natural" rhythm departs furthest from the "desired" rhythm. Mild DSPS cases are able to force the body clock to remain more or less in the desired bracket at the cost of a constant struggle with sleepiness. In more severe cases, the circadian variables will run a 24 hour cycle and the individual will experience return to "good sleep" when free running variables align again with the "desired" sleep period. The average sleep length is 6.8 hours but total sleep changes widely from day to day. The average DSPS shift is difficult to determine due to the battle against the natural rhythm. However, it is likely that the shift is around 60 minutes as evidenced by the average progression of the circadian acrophase estimate (in yellow). Without the use of an alarm clock, the advancing sleep phase would likely complete a full 24h turnaround in 3-4 weeks.

Resynchronizing the cycle In the next example, a middle-aged female with a severe case of DSPS experienced a similar struggle in stabilizing her sleep rhythm within socially acceptable limits:

Subjective sleepiness was minimum when the body succumbed to the progression of the sleep phase (Sep 16 - Sep 23), daytime tiredness increased markedly at the time of the battle with the progression (Oct 2 - Oct 11) where light aqua blue sleep blocks were blocks artificially terminated with an alarm clock. Finally, daytime drowsiness peaked in the period of lost synchrony between sleep periods and the circadian phase (Oct 19 - Oct 22). The breakthrough came with the religious adherence to free running sleep. The next log shows the same female on a well-managed free running schedule:

A perfect alignment of sleep periods with the circadian acrophase (yellow line in the middle of the subjective night) resulted in tripled energy and a sense of well-being.

Social life in DSPS Naturally, only people who are telecommuting, self-employed, or working from home office can afford to let their sleep run free in DSPS. Even then, the shifting sleep phase is a serious predicament. A legally blind DSPS sufferer from the Netherlands wrote about the pain of the shifting sleep pattern: "I am free running my sleep. I had an appointment at 17:30. I expected to wake up around 15:00 as in the previous three days. Instead I woke up around 17:00 still a bit tired. I had to skip my morning routine (meditation, breakfast, SuperMemo, etc.). FRS works really well for me. But today sucked. It was really stressing having to run due to waking up later than expected". After a medical consultation, this subject was prescribed evening melatonin and was able to stabilize his cycle (for at least a few weeks at the moment of writing these words). The torturous battle of the same subject with phase shifts before running free and before administration of melatonin is shown in this graph:

This example illustrates the major dilemma of all more severe DSPS cases. Free running sleep will often produce a phase shift. Anyone who tends to wake up very late is also highly likely to tend to wake up later each day in free running sleep. This is a hallmark symptom of the DSPS. DSPS, however severe, is never a health problem on its own if the sleep is run free. It is the scheduling problems that are most bothersome. The choice is between the two extremes:

either make one's life less dependent on meetings and appointments that can collide with your sleep schedule, or study DSPS remedies that can stabilize your sleep-wake cycle.

If you happen to always wake up late, waking up always at the same time makes scheduling much easier. If you do not opt for one of the above extremes (free schedule vs. stabilization battle), you will risk collisions that will make life pretty hard. What is even more dangerous, if one disrupts a circadian rhythm on a free running schedule, there can be a loss of synchrony between various circadian variables. This will result in a situation in which for a day or even a few days one is not sure of the optimum bedtime. Even SleepChart may be unable to make a good prediction. This will inevitably result in poor quality sleep, and a few days of low productivity.

DSPS: genes or lifestyle? Even though I keep repeating that the DSPS epidemic is a reflection of a modern lifestyle, genetic factors clearly play a role and the "creative personality" can also be at the root of the problem. Here is an interesting story of a writer mom whose parents and two kids do not show any signs of sleep problems, however, she suffers from a severe case of DSPS and so does her 20-year-old son: My mother claims I have had sleep issues from the day I was born. In those days "rooming in" was new as most babies were kept in the nursery and it was the norm for both baby and mother to stay in the hospitals for a week after a normal birth. She enjoys telling the story of how the nurses forced her to have me "room in" with her during hospital stay because I was "keeping up all the other babies in the nursery all night long" because I refused to sleep during nighttime hours. She said that after she and my father brought me home, I was afforded one night in the room with them but I was up all night so I had to "cry it out" alone from then on because I simply would not sleep at night. When I was a few years old, one night, exasperated, my parents said, "Fine. If you want to stay up, you can sit here and watch Johnny Carson." Apparently I was happy to do so! I did, however, have very unhappy memories dating back to the beginnings of my recall of being put to bed at around 20:00 every night and lying up awake and with nothing to do for hours and hours in my darkened, boring room. Back in those days, there was no Internet, no cable TV, no video games, no cell phones, etc. I simply could not get myself to sleep at a decent hour ever in my entire life! I'd often sing myself to sleep and it would take hours to do so. Sometimes I would run out of songs to sing and have to repeat a few until I passed out." Today, this self-employed female is experimenting with free running sleep and claims that, except for her social life that suffers as a result, the new schedule brought her back from the "hell of perpetual drowsiness".

Chronotherapy and its perils Chronotherapy makes it easy to fit the circadian phase into a desired time bracket, e.g. after an intercontinental flight, in circadian disorders, or for the sake of shiftwork. For most people, shifting the cycle forward by inducing phase delays is easier. It is possible to go to sleep 40-70 min. later each day and to cycle throughout the day until the desired sleep phase is reached. Pushing one's circadian cycle should always be the last resort. All artificial forms of sleep control should be avoided if possible as they are not healthwise neutral. However, some reports in the literature suggest that chronotherapy may have serious long-term cycle synchronization consequences. Wehr reports (Wehr et al. 1992[26]): "In 1983, one of us described a 28-year-old man with DSPS who underwent chronotherapy and found himself unable to stop his sleep period from rotating around the clock or restore his rhythm to a 24-hour schedule. Instead, hypernyctohemeral syndrome developed, with a persisting 25-hour sleep-wake cycle. This rare syndrome is extremely debilitating in that it is incompatible with most social and professional obligations". I have personally witnessed numerous cases of phase delays upon switching to free running sleep in seemingly normal people, and have a different interpretation. People differ in the degree of difficulty in sustaining a balanced 24h cycle in free running sleep. That difficulty is well expressed in circadian graphs by the angle of the sleep maintenance curve in reference to the breakeven line that determine a balanced 24h cycle. Most adolescents will experience a degree of difficulty in maintaining the balance if they are allowed to engage in their hobbies and passions late into the night. Once they are allowed to do as they wish, they will often induce phase delays by a simple unwillingness to go to bed "in time". Even though the progressive 24.5 hour cycle may seem unsettling at first, resulting in sleeping in unusual hours, the convenience of running free with extended waking days may outweigh the negative side effects. For people suffering from DSPS, running free may provide an unusual degree of comfort that is difficult to forfeit. No wonder that many DSPS sufferers, who enjoy a progressively shifting circadian cycle in free running sleep, often give up the battle to reset the cycle, or even discover that their natural phase shift is far larger than originally diagnosed. As the medical and psychiatric terminology of severe cases of DSPS is very confusing, I need to yet attempt to explain cases of "irregular Non-24-hour sleep-wake syndrome", by which I mean a severe DSPS where sleep episodes do not fall into a regular pattern. I have presented some cases in the Asynchronous DSPS section. I have little doubt that most of such irregularities come from subject's own ignorance of his or her sleep preferences, as well as the rules of a healthy free running sleep regimen in circadian disorders. Once a sufferer is instructed on the rules of healthy free running sleep, perhaps with some assistance from SleepChart, the sleep pattern becomes regular. My personal stance on chronotherapy is therefore as follows:

Chronotherapy is the best approach to repositioning the phase of the circadian cycle. It should always be the last resort as it is not neutral for the quality of sleep. However, long term consequences of occasional use of moderate chronotherapy are probably negligible.

Synchronous DSPS When a DSPS sufferer attempts free running sleep, sleep phase delays are inevitable. There have been cases in literature that documented people living along such a shifting DSPS schedule for decades without major health side effects (Neubauer 2000[31]). For an exemplary report see this blog[32]. Some authors claim that a shifting schedule may increase the incidence of depression, alcoholism, or dependence on sedatives (as a result of attempts to induce sleep at the "appropriate" time). The following graph presents a sleep pattern of a free running middle-aged self-employed male:

A very clear and regular DSPS pattern visible in the graph with a daily phase shift of 64-68 minutes. Although sleeping in "unnatural" hours is certainly less beneficial healthwise than normal sleep, for a DSPS subject, free running sleep rhythm may by far less stressful and disruptive than any attempt to fit to "standard" lifestyle. A very reliable determinant of synchronous DSPS is the loss of the link between the sleep onset hour and sleep duration (see: Preference for night sleep). As the duration of sleep is determined by the circadian phase, well-synchronized sleep schedule shows little variability in the sleep length (6.6 hours in the presented graph). In particular, the sleep length is independent of the sleep onset hour. Whenever the subject makes any attempt at synchronization with daylight or daylight-related activities, the link between sleep length and the onset hour will be reconstituted. Mistakenly, DSPS people are often called "owls" for their tendency to stay up late, while ASPS people are called "larks". The graph illustrates why this is a misnomer. A similar graph shows a DSPS case with an even greater degree of phase shift (84-90 min):

Due to a better sleep efficiency in episodes well aligned with the circadian cycle, people on a regular free running DSPS schedule report a much higher subjective alertness and energy as compared with those on an irregular DSPS schedule. This difference also shows up in data collected with SuperMemo.

28 hour day schedule 28 hour day schedule was proposed for those who seek higher productivity and more hours in a day. An example of a 28h sleep pattern design shows a phase shift that needs to reach the daily extreme of 4 hours per day for anyone to be able to sustain that schedule for a longer period of time:

28h day schedule design

The advantages of a 28 hour schedule supposedly include longer working days, regular 6 day week, repeatability, long weekends, increased energy, unlimited sleep, etc. (for more see: 28 hour day). This proposition is the other extreme of a spectrum of propositions that begins with polyphasic sleep. However, it seems far easier to sustain as it does not need to involve an alarm clock. Sleep researches believe that this schedule is so extreme that nobody should be able to sustain it in a long run. 4 hour phase shifts are so unlikely that researchers choose it for their experimental forced desynchrony protocols. These are experimental protocols in which the body is supposed to fail to adapt to the timing of zeitgebers. Such an entrainment failure is beneficial in studying free running circadian variables. 4 hours shifts have been used in both advancing and delaying protocols (20 hour days (Wyatt et al. 1999[33]) and 28 hour days (Carskadon et al. 1999[34])). All research to-date seems to indicate that the circadian cycle keeps running free in the background in forced desynchrony protocols due to the fact that resetting stimuli cancel each other out and sleep episode intersect with the circadian variables in unpredictable patterns that result in segmented sleep, premature awakening, shortened sleep, reduced REM, and other symptoms of asynchrony. In short, 28 hour day is considered extreme enough to cause perpetual lack of synchrony between the timing of sleep and the circadian cycle.

28 hour day in DSPS Some sufferers from DSPS report feeling better on the 28 hour schedule than on a conventional 24 hour sleep schedule. I do not think it is likely there are individuals out there with an innate ~28 hour circadian cycle, however, it is conceivable that the effort to squeeze a DSPS cycle into 24 hours is more painful than the alternative in the form of stretching the cycle to 28 hours. The main difference is that the shortening of the cycle usually involves the painful use of an alarm clock, while stretching the cycle requires "only" extra 2-3 hours of zombified wakefulness. Even in severe DSPS, it should be pretty hard to adapt one circadian cycle to the 28 hour schedule as the phase response curve indicates that the sleep phase does not respond strongly enough to strongly delayed bedtime, which may, in extreme cases, cause a phase advance. Phase delays beyond 2 hours should be extremely rare. For most people, it is pretty hard to tolerate even minor deviations from one's optimum cycle period. For this reason, all designer schedules should be avoided unless they come from a strict analysis of one's own sleep preferences. Again, free running sleep is a better option, even though it may be less predictable and less convenient in planning one's social or professional life. Let us consider an exemplary case of Subject S, and compare her sleep efficiency on conventional, 28 hour, and free running schedules.

Conventional schedule in severe DSPS When S attempts to adhere to a conventional sleep schedule, under medical supervision, with the help of sleep medication (incl. melatonin), the sleep is strongly fragmented, short, unrefreshing, and the schedule is unsustainable:

Subject S on an unsustainable conventional schedule.

This type of sleep is tantamount to mental torture, and all individuals with a similar degree of entrainment failure should always be allowed to let their sleep run free on the grounds of severe disability. In the presented chart, a pattern of possible free running circadian cycle can be noticed in the chart with the subjective night leaving the conventional night bracket around April 6, 2011. This is more noticeable upon sleep episode consolidation:

Subject S on an unsustainable conventional schedule (sleep episodes consolidated).

Needless to say, the conventional schedule, if maintained for longer, may lead to serious health problems due to the state of persistent sleep deprivation compounded by medication. Even though the presented case is pretty drastic, the number of people suffering from similar sleep problems is constantly increasing and is definitely affecting overall population health and productivity.

28 hour schedule in severe DSPS When S attempts to adhere to a 28h day schedule, her subjective sleep quality increases dramatically along with the total sleep achieved. Detailed analysis of the sleep chart, however, shows that sleep fragmentation is still substantial showing strains in the sleep control system:

Subject S on a 28h day schedule.

Segmented sleep starts showing after two cycles which might indicate that the actual phase shift lags behind the planned phase delays. Segmented sleep is often a sign of premature bedtime and shows up when the 28h schedule bedtime falls ahead of the presumed free running subjective night. When the sleep schedule undergoes an eventual collapse, the positioning of lengthy recovery sleep episodes seems to indicate that the average daily phase shift might have actually been much less than 4 hours. In an extreme case, large disparity between the subjective night and the planned nighttime might result in self-cancelling phase shifts that might paradoxically stabilize the sleep cycle. Circadian graph for the same 28h day schedule illustrates the degree of chaos in the sleep control system:

Circadian graph for Subject S on a 28h day schedule.

Free running sleep in severe DSPS When the sleep chart of Subject S running free just a few months earlier is inspected, the sleep phase shift is closer to a mere 41 min per day (as opposed to 240 minutes needed to smoothly sustain the 28h day schedule):

Subject S on a free running schedule.

However, the chart shows that even in that period sleep was strongly fragmented and irregular. Similar analyses are often misleading due to compounding circumstances such as a disease, family problems, medication, and even a wrong choice of bedtime (e.g. in an attempt to stabilize or accelerate the cycle). In similar cases, it is paramount to chart one's precise circadian preferences. For this reason, a few weeks of uninterrupted free running sleep would be precious to determine one's natural innate daily phase shift. Once this is done, more can be said about the sustainability of a 28h day schedule for a given individual. However, continual free running sleep is always the best option for those who are absolutely unable to balance the cycle and those who can afford the sleep schedule that is hard to reconcile with the rhythm of the outside world. See: Curing DSPS and insomnia.

Curing DSPS and insomnia If you cannot live without an alarm clock to wake up in time for school or work, you might be suffering from a delayed sleep phase syndrome (DSPS). DSPS is also associated with problems with falling asleep if you try to keep an earlier bedtime. In other words, any cure for DSPS is also likely to solve the problem of sleep onset insomnia. If you go to a sleep expert with your DSPS problem, you will likely be prescribed melatonin or a bright light therapy only to discover their limited impact on the quality of your sleep. If you are an insomniac, you may additionally be prescribed sleeping pills that might help you sleep without achieving the desired effect: a refreshed mind. This chapter should help you solve the problem. Using the properties of the human sleep control system, it can be proven mathematically that the problem of DSPS, and the associated insomnia, is always solvable, however, the solution does not need to imply the crispiest mind or the highest intellectual productivity. Moreover, many people will still fail due to the lack of self-discipline! Where modern world encroaches upon human biology, it is still possible to withstand the tide with the rules of reason. However, these imply a religious adherence to the decalogue of healthy living. Life shows that humans find all decalogues difficult to abide by!

Solution for insomnia, DSPS and N-24 This algorithm should help you in all the following cases:

if you are an insomniac, your body most likely tries to sleep in a different phase, if you fix the phase, you will fix the insomnia if you are a DSPS case, esp. a long-term sufferer, you will be very skeptical of the algorithm. You need to give it at least a few weeks of well-disciplined try to see that your sleep cycle can be modified with the right tools if you are a Non-24 and you believe there is no pattern to your sleep, you are most likely wrong. There are rare mutations that can totally mess up your sleep, but a more likely explanation is that you are a DSPS case who just introduces enough chaos into your sleep pattern to make it seem unpredictable. If you are otherwise healthy and if you try free running sleep, you will notice the pattern. For the pattern to emerge your "free" sleep must truly be free. No regulation. No artificial control! After that, you can try the algorithm presented below to see if you can show enough self-discipline to set your cycle stable.

DSPS and lifestyle Even though there are various genetic influences that play a role in DSPS, the problem is, for most people, largely a matter of lifestyle. I claim that due to the fact that a return to a farmer's lifestyle provides a guaranteed disappearance of the DSPS problem. Below, I have compiled a simple algorithm that should resolve DSPS in a vast majority of cases given sufficient self-discipline. Until now, I have been far more successful in showing people how to cope with DSPS using free running sleep than with the prescription listed below, which is a derivative of free running sleep with some limitations targetted at preventing a phase delay. The presented algorithm fails primarily because of one issue: violation of the rules! There are true hardcore DSPS cases with some psychiatric overtones or other health issues that might be particularly intractable, however, those should form a rare minority in the ever-increasing mass of people struggling with DSPS. That mass now includes a countless population of insomniacs who have never heard of DSPS and never even arrived to the problem of phase shift due to the employment of the alarm clock. Weitzman hypothesized that a significant number of patients with sleep onset insomnia might be suffering from undiagnosed DSPS (Weitzman et al. 1981[35]). Now we know that hypothesis certainly holds true, which can be demonstrated by letting insomniacs free run their sleep. A significant phase delay may be observed within the first few days of such a release from the restrictions on the timing of sleep. At the same time, there is an accompanying and nearly instant disappearance of sleep-onset insomnia.

Implausible solutions People who suffer from DSPS often resort to their own implausible solutions that include:

(poorly managed) free running sleep with an inevitable phase delays that ultimately result in sleeping through the day skipping a night of sleep at a point when the bedtime reaches an outrageously late hour (i.e. usually after the dawn) stabilization of the sleep pattern with medication (incl. melatonin) and artificial zeitgebers such as an alarm clock or a mom who pulls a sleepy student out from his or her bed for school messy sleep that occurs at unpredictable hours with the loss of sense of the nighttime and long bouts of drowsiness, low energy, or poor health. This sleep pattern is often labelled Non-24 or N-24, however, in most cases it differs from DSPS only in the lack of self-discipline or knowledge needed to adhere to a natural sleep cycle, even if its period is longer than 24 hours

Only a well-managed free running sleep can produce healthy sleep in DSPS with a minimum risk of negative health outcomes. However, very few practitioners do really adhere to the rules of their own body clock as there are always excuses or inescapable reasons to violate the subjective night when it collides with daytime obligations or diversions. People who try to "free run" their sleep in DSPS for many years are at a risk of messing up their sleep control system. I conclude that from the fact that their sleep patterns often become less and less regular[32], and the quality of their sleep often decreases. This effect would almost certainly be minimized if the sleep was truly free without medication, light therapy, artificial delays, or the use of the alarm clock. They may even falsely claim that their cycle started getting longer and longer, while it is the lifestyle demands that keep stretching the waking time. The culprit here, naturally, is not free running sleep per se, but various violations thereof that are inevitable due to a conflict of sleep with daytime activities.

Plausible solutions If we exclude a healthy farmer's lifestyle and the renunciation of evening electricity, we arrive at only two reasonable lifestyle solutions to the DSPS problem:

(well managed) free running sleep with phase delays, high creativity, high productivity, good health, and schedules that are nearly impossible to reconcile with the outside world stable 24h sleep cycle, with monastic self-discipline, good health, and lower productivity

I write about free-running sleep throughout this article. I worship free sleep so much that I have been accused of labelling DSPS with the stamp of incurability. Here I would like to present a plausible algorithm for sustaining a 24h sleep pattern in DSPS with minimum artificial intervention into the fabric of sleep.

The algorithm The only reasonable 24h solution to the problem of insomnia and DSPS is the change to the sleep phase. We can advance the sleep phase using evening measures (pulling the sleep backwards) and morning measures (pushing the sleep backwards). That takes care of the circadian component of sleep. In addition, all measures that boost homeostatic sleepiness in the evening are also welcome. However, without the circadian components those might actually compound insomnia. This is why only a comprehensive approach, as presented below, provides a solid chance you will leave your DSPS and/or insomnia behind:

Determine the length of the day: Use SleepChart to determine your optimum length of the waking day. You may need a few weeks of free running sleep data to make a good estimate. If you cannot free run, and/or the procedure seems too complex, you could just make an educated guess. For example, if you believe you need 8 hours per night, in free running sleep it might be closer to 7 hours, and your optimum waking time would be 24-7=17 hours. However, due to the problem of possible insomnia, it makes sense to start from a slightly longer day and shorter sleep, e.g. from 17.5 hours of waking. Determine the preferred waking time: This should be the same time every day! If you have to get up early only once per week, your entire cycle should be positioned to accommodate that early hour, or you will risk never-ending ripples in your circadian system and a possible failure. If the waking hour is late enough to ensure bright sunlight in the morning, your chances will increase greatly. Religious bedtime: By adding your optimum waking time to your chosen waking time, you will get your optimum bedtime that must be respected religiously. This respect is one of the keys to success. You will encounter many obstacles in the process. One of the most confusing ones is the change to your optimum waking time depending on the contents of your day, your activities, your stress, weather, season, social interaction, and so on. For most people those changes are less than one hour. However, you are more likely to be in the wild variations category as this is one of the underlying problems in DSPS. Start adhering to your optimum bedtime as if your life depended on it. If you are very excited or stressed, and you are not sleepy at your bedtime, you can try again 20-30 min. later. You need to be sure you won't toss and turn, and that you do not wake up prematurely. If you see any signs of insomnia, you will know your bedtime comes too early and you allocated too much time for sleep. If you are very sleepy ahead of your bedtime and you have no doubts you will sleep like a log, go to sleep earlier. Your optimum bedtime is the guidance, your actually sleepiness is the ultimate yardstick. Start the algorithm. Ideally, you should start the algorithm at a time when your waking time precedes your desired waking time. Otherwise, you may need to temporarily resort to using an alarm clock. However, each use of the alarm clock will add to your stress and anxieties related to early bedtime. If you have to use an alarm clock, and if you struggle with getting up in the morning, you should consider taking a full free running cycle with a daily delay of 20-40 min. until you arrive at getting up comfortably 2-3 hours before your chosen waking time. You could then try to re-start the algorithm. Protected zone: As you suffer from DSPS, your primary objective is to prevent phase delay. This means that, in your last 2-4 waking hours, you need to avoid light, electricity, excitement, stress, intense sports, TV, computers, social interaction, e-mailing, web surfing, etc. If the presented algorithm does not work for you for a longer time, you may have to extend this "protected zone" up to a point where the resulting "inaction" results in more stress or frustration than it actually eliminates. Extending the protected zone beyond 2-3 hours of dark silence will probably be counterproductive. See for yourself. Remember, that the protected zone is not a time for lying in bed! Unproductive time in bed will add to your stress, and if you fall asleep early, you can mess up your sleep on that night and actually delay the phase! Obviously there is a very limited range of activities you can do in the protected zone. I leave it up to your imagination. Perhaps moderate exercise in dim light. Or sex? Or walking and thinking? Seth Roberts swears by one-legged standing before sleep. Morning light: One of the most powerful zeitgebers is light. If sunlight can stream into your room at the time when you should wake up, you might eliminate half of the difficulty in achieving a 24h balanced cycle. If this is impossible due to the season, or your early waking hour, or your living arrangements, you might consider using one of the commercial devices used in the "bright light therapy", esp. if you turn on the lights with the timer (if your device has no timer, you can use a timer that cuts off the supply of electricity for the night). Please be sure you read all the relevant safety instructions to prevent any long-term impact on your health. Morning exercise: Another powerful zeitgeber is outdoor exercise. If possible, you should schedule that exercise early in the morning, or at least in the first 5 hours of the day. Morning exercise will affect your intellectual performance. You will most likely tire faster. However, this is also one of the factors why exercise should help you sleep better. Intense exercise late in the day may have the opposite effect and might delay your phase. However, some forms of exercise will not have this effect as the phase-shifting stimuli will be counterbalanced by the amplification of the homeostatic sleep drive and the "fasting effect" that will help you sleep early. Those evening exercises should be free of stress, injury, emotion, etc. Gentle calisthenics, yoga, or stretching would be an example of harmless evening exercise. Perhaps even body building, if not too exciting or strenuous. This late exercise would best be performed in dim light and in absence of other rousing stimuli. If you can swear that evening exercise helps you fall asleep faster, even if strenuous, remember that sleep itself has a phase-shifting power and can actually outweigh the opposite effect of adrenaline or locomotor activity. If you are not sure, experiment on your own. Evening fasting: Unless you are a ravenous type that cannot sleep without a snack, give up meals in the last couple of hours of the day. As explained in the DMH section, food may have an additional impact on the positioning of your circadian cycle, and you do not want your brain to think that evening is an opportune time to get food. A healthy breakfast in the morning should have the opposite effect on the sleep phase and is always recommended by nutritionists even if sleep phase delays are not in the cards (note that Seth Roberts recommends skipping breakfast, but this should apply to those who suffer from early waking or ASPS, not for onset insomniacs or DSPS). Don't be discouraged by research that may claim that evening fasting will not affect your circadian cycle. For example, Sensi found that morning meals seem to favor carbohydrate metabolism, and meal timing, within the studied range, did not impact circadian cycles (Sensi and Capani 1987[36]). Fasting has many other added benefits, incl. slimmer waistline. Try it for yourself and see the impact of evening fasting on your sleep and health within a week! Read more: Fasting. Adding pressure: If you keep failing by waking up too late, or not being sleepy at the desired bedtime, keep adding up pressure at both ends of your night sleep. More exercise in the morning, brighter lights in the morning, longer protected zone in the evening (free of stress, computers, lights, TV, etc.). The harder your case, the more you need to add. Choose a day free from other obligation for an exhaustive exercise marathon (which, for you, may be just a few hours of brisk walking), and spend the evening on undemanding relaxing activities that will help you advance your bedtime. You will need to figure out for yourself what exercise intensity ensures you do not wake up prematurely and what advance you can actually afford without making the situation worse. Emergency: Melatonin: If your "protected zone" is stretched to the limit. You may consider an occasional pill of melatonin (e.g. 2 hours before your optimum bedtime). Remember that melatonin will affect your creativity and alertness, and should not be used on a regular basis. You could resort to melatonin on days when you are particularly wound up or when your waking time was particularly late. Remember also that large doses of melatonin may backfire. I guess you should not ever exceed 3 mg, however, you would better consult your sleep expert to make the final decision as to the dosage and timing. If you keep failing with the algorithm, you should rather increase the frequency of taking melatonin. You should not increase the dosage! Do not use marijuana as a "melatonin substitute"! If you think that your sleep and your brain performance do not suffer on MJ, you are wrong! Emergency: Radio timer: As the algorithm is supposed to let you sleep without an alarm clock, you cannot expect to wake up at the same time every day. Actually, the larger your DSPS problem, the larger the variations you may expect. Achieving a very regular waking time is a matter of practice that some good sleepers develop over many years of repeated habits. However, if you regularly oversleep by more than an hour, or even still experience the dreaded phase shift, you may consider some occasional mild form of artificial sleep regulation such as turning on your alarm radio at the minimum sound level. Such a gentle alarm is only to help you wake early from the shallowest stages of sleep early in the morning. It should not deprive you of valuable REM sleep, and it should absolutely be set below the level that could rouse you from deep sleep. Your goal will always be to get rid of any interruption or intervention in the morning. Consider this only as a temporary measure that may help you in the initial adaptation period that is bound to include minor failures. You have probably heard of alarm clocks that read your sleep phase and help you minimize the pain of waking. I am not a great enthusiast of such solutions. The concept makes sense, however, it only minimizes the pain of possibly cutting a vital portion of your sleep. Set up an On-timer in your TV, on your favorite channel, at a minimum volume. If it fails to wake you up, you will know you need to work on other points of this algorithm. Trying to wake up for a specific hour is stressful enough to act as a substitute alarm clock that works for many people pretty well. Some scientists believe that ACTH secretion is set to ensure timely waking. I believe that this type of compacted sleep is still better than the one interrupted by alarm clock. At the very least, natural waking after short sleep definitely feels better than sleep interrupted at its deeper stages with an alarm clock. In conclusion, you should remember that your determination to succeed is also an important component of the algorithm. Determination may be unhealthy, it might affect your hormonal profile in sleep, it may weaken your immune system, however, balancing DSPS without giving up modern lifestyle will always have some residual negative health effects. Only a return to an ancient lifestyle would provide a hermetic solution. Napping: A very controversial issue in DSPS is napping. Many experts will tell you that you should avoid napping altogether. I disagree. Naps may cause a phase shift if they are taken too late. Early naps, e.g. taken in the 6th hour of your waking day, will not have this effect. Naps will help you get your evening productivity, esp. if early waking in bright sunlight or early exercise aren't too good for your morning alertness. If you keep failing to achieve your 24h balanced cycle, you can gradually shift your naps to earlier hours. This will reduce their length and their efficiency, however, this will also minimize their phase shifting effect. Only if all other suggestions fail, you should drop napping altogether. If you bemoan the loss of mental acuity, remember that we have not evolved to be alert and productive all day. 100% sharp mind is only our desire that has, among others, contributed to the DSPS problem in the first place. See: Best nap timing Caffeine: Sleep experts will often tell you to wean yourself off caffeine. However, I beg to disagree. A cup of early morning coffee or tea will likely have a beneficial effect. Its impact on the homeostatic sleep drive will increase your alertness, which on its own has a phase shifting power. Early caffeine will help you advance your phase! You should avoid caffeine in the later parts of the day though. Before sleep you will already be in mild withdrawal, which, theoretically, should boost your homeostatic sleep drive and allow for a slightly earlier bedtime. This way, caffeine may help you achieve phase advances at both ends of your night sleep. Alcohol: Drinking alcohol before sleep may have disastrous effects on your effort to balance the cycle. One of your major enemies will be premature waking after premature bedtime. Alcohol will increase that risk manifold. Premature awakening will result in insomnia, in powerful phase shifts, in difficulty in waking, in sleep deprivation, and in an early collapse of all your efforts! Western culture is generally tolerant of moderate drinking in the evening as opposed to the morning when we are supposed to be productive. I think this tolerance should change. As much as early drinking undermines the thinking, evening alcohol might do even more damage by destroying sleep. Stress: Stress can ruin all efforts presented in this algorithm. Wherever possible, try to pile up stress in the morning, and let the second half of the day be always free from worries and anxieties. Naturally, stress that lasts for days is a general enemy of healthy and productive living. If this is your problem, please have a peek at the stress section of this article to see if you can find any useful hints there. Myopia: If you are shortsighted, you should consider getting a correct prescription. Some theories of myopia favor underprescription (Rehm 1981[37]), however, you will also find evidence to the contrary (Coghlan and Le Page 2002[38]). If you lean to the underprescription side, consider using the correct prescription only in the morning. Only the first 2-4 hours matter. You may recall from your physics class that the amount of light reaching the retina will actually be reduced with the increase to the focal power. However, well-focused light will be more likely to produce strong maxima with a phase-shifting power. Analogously, you might also consider using dimmed spectacles in the evening. Naturally, these are not recommended for "close world" applications (such as reading the computer screen) as these might accelerate the progression of myopia. Computer screen: There are computer screen filters and applications that can help you filter phase-shifting light frequencies that can dim your monitor in the late evening. I hear from users of those applications that they are helpful in their DSPS battles. As always there is a risk this might be a placebo effect. However, the cost of trying isn't high. Difficulties: If you keep experiencing phase shifts, move your siesta to an earlier time, or give it up altogether (at last until you regain the balance). Use emergency measures (melatonin, radio news) only as a last resort. If those last resort solutions keep being necessary, it may appear that a shifting free running sleep cycle does less damage than trying to stick to a "healthy" stable rhythm. Review all the recommendations on this list. Did you employ them all? Did you show self-discipline? If so, it should work in most cases. All the failures I have seen came from rather flimsy excuses and minor violations. All the success I have seen came from treating sleep regimen as a religious routine. If all else fails, write to me with your story. Target: In the initial period, lack of experience, misalignment of sleep control variables, sleep debt, lack of conviction, etc. will make it a bit harder to stick to the presented algorithm. This is particularly difficult for those who do not need to get up early for work. Their mind might vacillate. Is early rising worth the effort? It may therefore be psychologically helpful to begin one's sleep reform 3-4 weeks before an important event that requires early rising. The thought of participating in an important event with a fresh mind will increase the motivation to adhere to the rules. Creativity dip: Once the presented algorithm works for you, you may be disappointed to notice that your creativity isn't as rampant as on those weekends when you get your solid 8 hours of sleep, or when you go to sleep at 5 am (whichever is your cup of tea). That's the unavoidable cost of sleep phase resetting and phase advance measures. We have evolved to live 24h lives with a primary concern for surviving, getting food, etc. Crisp or creative mind isn't that important when you are to run away from a predator. When you meet a lion on a street, you are bound to be in your top shape for flight. The degree of your creative decline may be proportional to the degree of the original problem as well as the length of the period in which you tinkered with your sleep control systems using the alarm clock, sleeping pills and other brain health enemies. It works! Remember that every healthy individual can stick to a 24 hour cycle on a farmer's lifestyle. Some disabilities, e.g. blindness, may make it impossible, but these should only be an exception to the rule. At worst you could try out the farmer's lifestyle to realize that it solves your sleep problem, and then try to reconcile that extreme with the presented algorithm. There is an optimum for you somewhere in-between and it does not need to be unhealthy. Ultimate cure? The title of this chapter should not make you think that you can cure DSPS for good. It is always there. You can temper your response to the temptations of modern life and return to a balanced sleep pattern as your reward. Your lifestyle is your cure.

Outcome: Balanced 24h sleep cycle! If you use SleepChart, you can see the impact of the presented algorithm in the circadian graph. Exemplary outcome of the application of the presented algorithm is presented below:

Perfectly balanced 24h cycle in DSPS.

In this example:

the green line determines the conditions for the balanced 24 hour cycle (waking time + sleep time = 24 hours) the nap is taken in the 7th hour from arising (the left blue peak) and lasts 1.2 hours (the left purple vertical line). The nap is used to partly compensate for a short nighttime sleep the optimum length of the waking day is 18.3 hours and is determined by the crossing of the green line that determines the 24h sleep-wake cycle and the average sleep time depicted by the red curve. Shorter day is possible but entails a risk of sleep-onset insomnia. Longer day will result in phase delays (the area where the red line is located above the green line) the optimum length of the night sleep is 5.7 hour (horizontal orange line). the cycle implies 5.7 hours of sleep in the night and nearly 6.9 hours of total sleep, which might be equivalent to 9 hours of nighttime sleep in monophasic sleep (see: Optimum nap duration)

Summary In the presented algorithm, you try to stick to your optimum bedtime and waking time every day. You establish a protected zone in the evening to favor phase advance (minimum light, computers, stress, excitement, etc.). You wake up to bright sunlight and use morning exercise to advance the phase in the morning. You ingest caffeine only in the morning. You avoid alcohol in the evening. If you nap, you nap early. If your phase keeps shifting, you add more light and exercise in the morning. You also extend your protected zone in the evening. In emergency, when you fear falling out of synch, you could occasionally use melatonin in the evening, or delicate sounds in the morning as the minimum effective departure from the free running sleep principle.

Advanced Sleep Phase Syndrome (ASPS)

Advanced Sleep Phase Syndrome (ASPS) is the opposite of DSPS. People suffering from ASPS get very sleepy early in the evening and wake up very early in the night. Their circadian clock runs at less than 24 hour period or get easily reset in the morning (e.g. by stress). ASPS people constantly struggle to survive awake to a reasonable evening hour, sleep less, wake up early, and experience increased tiredness during the day.

Genes and lifestyle in ASPS ASPS often runs in families and is then called familial ASPS or FASPS. Some mutations that may cause ASPS are listed in this table. While a typical DSPS person is an adolescent student, a typical ASPS person is a retiree or a middle-aged woman with low stress tolerance. The link between the age and sleep phase disorders may be related to aging itself, however, it may also be a result of lifestyle changes that come with age. Remarkably, while I have received dozens of SleepChart submissions showing a free running DSPS pattern, I had to actively seek submissions that would illustrate ASPS. This alone can serve as an illustration of personality and lifestyle differences between the two groups. It is the DSPS group that keeps surfing the net till the early morning hours in search for a solution to their sleep problem. In the end, they often arrive at supermemo.com, download SleepChart, and begin logging their sleep in an effort to understand their own sleep patterns. The ASPS group is usually in bed early and often not refreshed enough during the day to seek a solution on the web. I have not received even a single reverse ASPS pattern with sleep starting progressively earlier in the day!

Example 1: ASPS and substance abuse

The presented SleepChart log illustrates a stabilized ASPS sleep pattern of a postmenopausal unemployed female with a lifelong history of substance abuse, currently in a period of abstention and recovery. Without medication, the subject struggles to stay up past 5 pm. She often wakes up at 1-3 am and finds it impossible to fall back asleep. She reports a perpetual tiredness. The only solution to her sleep problems seems to be sleeping pills regularly prescribed by her GP and/or psychiatrist(s). Those pills have also been a part of a vicious cycle of addiction to benzodiazepines and alcohol. Superficially, the log seems to look like a picture of a perfectly healthy sleep. However, the entire schedule and the sleep phase are kept in check with a cocktail of psychoactive drugs. The main difference between this ASPS case and a similarly-looking perfect sleep case is the said persistent tiredness throughout the day. The subject reports that her chief preoccupation is to "somehow get through the day" when combating tiredness, and struggling with an ever present threat of a fallback into addiction. The difference in sleep length on individual days (8-9 hours on good days, 0-3 hours on bad days) comes from the fact that the subject sleeps at different family locations on different days. Some of those are considered better (resulting in better sleep), others are considered more stressful. One of the nights was sleepless due to family stress. This illustrates again how lifestyle determines sleep patterns. Sleep maintained with drugs always yields fractional cognitive benefits. In this case though, the effect is truly dramatic with cognitive performance comparable with that encountered in a state of severe intoxication. The drugs schedule, which changes periodically for various reasons, is invariably composed of pick me ups in the morning, and put me downs in the evening, as well as some "extras" for controlling various neural side effects of the "sleep control cocktail". Individual drugs interfere with each other producing a constellation of side effects that result in a horrendous chaos in the system, and long-term consequences that in turn result in an inevitable spiral towards a psychiatric decline and dramatically reduced well-being, ability to function in society, and longevity. The half-life of opposing drugs results in their effects cancelling each other and producing unpredictable resultant consequences. Why is then this pharmacological horror tolerated? For an unemployed individual with a history of substance abuse, for his or her family, and for the doctors involved, anything that resembles normality today takes precedence over the long term consequences. Naturally, for nearly everyone involved, this zombified status quo is preferred to actual intoxication even though that both are bound to destroy the brain in the long run. EEG findings indicate long-term and largely irreversible changes in the function of the central nervous system caused by substance abuse and/or psychoactive medication. As with all medical intervention in general, psychiatry is particularly troubled with tunnel vision that fails to see the big picture of individual's life and population health in general. New drugs pop up too fast to effectively study their long-term consequences. They are subject to prescription fashions that wax and wane. As barbiturates gave way to benzodiazepines, and benzodiazepines to Prozac, a well-meaning psychiatrist is often confused by a welter of contradictory data, never-ending lists of contradictory side-effects and the scourge of scientific observation: guaranteed false data coming from patients who always have multiple reasons for lying to their doctor. Making all patient history records near-to useless. Patients often change doctors to suit their dream prescription, or seek parallel advice and contradictory prescription from different sources. They rarely stick to the drug timing and dosage. For the record, at the moment of writing, the drug array in use in the presented example was:

antidepressant venlafaxine that is able to lengthen the period of the circadian cycle (8 am, half-life 10 hours) antipsychotic aripiprazole (8 am, half-life 75 hours) anxiolytic benzodiazapine lorazepam (6 pm, 2.5 mg, half-life 15 hours): in use for years instead of the recommended weeks, despite various side effects including severe sleep apnea; possibly the prescribing physician was not aware of the fact antipsychotic olanzapine (8 pm, 20 mg) in addition: anticonvulsant lamotrigine (50 mg)

As of the moment of writing, I was not able to ascertain if these have been prescribed by a single psychiatrist and if the prescribing physician(s) had an insight into the patient's full medical history.

Example 2: Overmedication and daytime drowsiness The second example shows another severely medicated case. 56-year-old male retiree carries on on an equally potent cocktail of drugs. In this case, poorly-planned irregular free running sleep helps reveal the degree of daytime sleepiness with sleep episodes initiated regularly starting with the 3rd hour of wakefulness, short and early forbidden zone in the hours 7-9, and preference for short waking day of 12-18 hours:

Perhaps due to the impact of the sedatives, the length of sleep episodes may reach an equivalent of a full night's sleep at practically any time of the day. Needless to say, the subject is hardly able to function cognitively and complains of never-ending tiredness. The drugs used in this case:

between 7-8 am antidepressants: aripiprazole (5 mg) and bupropion (150 mg) around 11:30 am: an antipsychotic quetiapine (25 mg) around 9 pm: benzodiazepine clonazepam (1 mg), antidepressant escitalopram (40 mg), lamotrigine (200 mg), quetiapine (50 mg) in addition: tamsulosin to avoid nighttime urinary incontinence

Phase shift graph

The phase shift graph may be used by people in free running sleep suffering from ASPS or DSPS. This graph shows the degree of phase-shift as well as its dependence on the time of day. The graph can be used to see the expected bedtime given a specific natural waking time:

Blue line shows the bedtime (vertical axis) for days with a given waking hour (horizontal axis). Red line shows the next day's waking hours (which are shifted by 1-2 hours in DSPS). Fuchsia and gray lines indicate the siesta period. Even though the red waking line begins at the origin of the graph, it shows a substantial phase shift at later hours (DSPS). From the presented exemplary graph one can read that for the waking time equal to 7 am (horizontal axis), the expected time to go to bed, as indicated by the blue line, is 1 am (vertical axis), while optimum siesta time occurs between 15:00 and 16:00. However, if the wake time is 11 am, the bedtime is likely to come only at 5 am the next day. Remember! Each individual will have a his or her own unique graph. Moreover, the graph will look differently if it is taken at times of work or at times of summer vacation. It will be affected by stresses at work and at home. It may even change when you move from one house to another, or when you change the climate zone. The graph will accurately reflect your rhythm only if you adhere to free running sleep. If you use an alarm clock, this graph will be meaningless!

Correlates of sleep phase syndromes

It is not known which are the predominant underlying physiological factors that result in sleep phase disorders. Family clusters show that genes may affect the length of the circadian period. The lifestyle will affect the levels of neurotransmitters and via their impact on the sleep phase will affect the period of the circadian clock as well. Lifestyle also affects the timing of zeitgebers (e.g. late night web surfing in DSPS). Conversely, the level of neurotransmitters may select for a specific lifestyle choices. Age may have a direct impact on the clock circuits, it may affect neurotransmitters, or it can affect the lifestyle. Last but not least, sleep phase disorders will affect the mood and the levels of neurotransmitters in varying ways depending on whether free running sleep is used to remedy the disorder, or whether the individual attempts to fit a predetermined desirable sleep schedule. Subsets of circadian rhythm sleep disorders (CRSDs) are strongly correlated with certain personality characteristics, and may have a strong genetic background. DSPS is more prevalent among adolescents, while ASPS is more frequently observed in an aging population. Women prevail in ASPS, while a slightly larger proportion of males suffer from DSPS (Sack et al. 2007[39]). Impaired vision often leads to DSPS due to a lesser impact of light on the circadian clock. DSPS is by far more frequent among students, programmers, avid readers, passionate artists, writers, computer game addicts, etc. It is possible that the same characteristics that help individual's creativity may also lead to problems with falling asleep early. ASPS seems more likely in individuals whose life is deprived of intense stimulation (esp. in the evening), who meet fewer new challenges, who are less passionate about their job or hobbies, or who are not facing information overload and the related stress, etc. Perhaps this is why ASPS is more prevalent in the elderly. For hormonal reasons, its prevalence also shows a sharp increase around the time of menopause in women. ASPS tends to run in families. A number of genes have been identified to be involved in FASPS (familial ASPS)(see: Clock genes and mutations affecting the clock period(Golombek and Rosenstein 2010[40]). There is a complex relationship between DSPS/ASPS and psychiatric disorders. 25% of people who could not maintain their 24h sleep-wake cycle were suffering from a psychiatric disorder (Hayakawa et al. 1998[41]). Some psychiatric disorders or the prescribed medication may induce DSPS, while, at the same time, DSPS conversely may cause various psychiatric symptoms. On one hand, there may be a link between DSPS and manic personalities. Anti-depressants tend to increase the period of the body clock (e.g. clorgyline, imipramine). On the other, paradoxically, DSPS individuals may be more likely to suffer from depression (e.g. when suffering from persistent insomnia, sleep deprivation, and the resulting social problems, etc.). Dr Daniel Kripke concluded that DSPS phenotype is familial and is associated with unipolar depression (Kripke et al. 2008[42]). However, the epidemic of DSPS in creative individuals suggests that those correlates need further investigation. Perhaps some contradictions can be explained by the fact that the state of mind of a DSPS sufferer depends largely on his or her ability to get sufficient and properly timed sleep? Thus more on a naturally manic side when sleep-satisfied, e.g. on a free running sleep schedule, and more on the depressed side when in circadian trouble (e.g. when forced to an early waking schedule)? Similarly, low-stress tolerance depressed individuals are more likely to suffer from ASPS. Again, when they are forced to adapt to "normal" life, their symptoms of depression tend to weaken either due to a sense of higher productivity or due to the fact that mild sleep deprivation counteracts the depression. The cause-effect relationship between sleep phase disorders and mood disorders is complex. Understanding it will contribute substantially to mitigating the escalating epidemic of sleep problems.

Baby sleep

How to make babies sleep well? People often say "I slept like a baby?" A joke says that it means that you wake up every 2 hours and scream. Indeed, babies tend to wake up in the night and seem unhappy (unless immediately soothed with mama's breast). This seems unnatural, unnecessary, and worrying. And yet babies have been designed to wake up many times during the night to feed. The net is jam-packed with an assortment of advice from and for young parents who seek good sleep for their babies and for themselves. A great deal of that advice is based on myth and/or pseudoscience. If the advice includes the word "train" or "schedule", you need to triple your skepticism! Even world renowned pediatricians overemphasize the "routine" over the actual natural sleep mechanisms. As much as adult's, baby sleep is ruled by homeostatic and circadian mechanisms, and any attempt to override those is futile and potentially harmful. All routines such as rocking the baby, quiet room, feeding, quiet talking, music, etc. are welcome as long as they are not attempts to enforce a sleeping schedule on a baby. These routines are little more efficient in inducing sleep as all the grandma's advice against insomnia. Neither homeostatic nor circadian mechanism is trainable (beyond natural phase shifts, etc.). Babies should sleep on demand (ad libitum), i.e. only then when they are sleepy and want to sleep. Nevertheless, understanding their circadian patterns can be very helpful in assisting the routine. As baby sleep is more complex than adult sleep, you can use SleepChart to see through the chaos. This can help as guidance. Nevertheless, observing the symptoms of sleepiness is the oldest and the best practice. Some moms claim proudly "my baby sleeps through the night". However, when actual sleep logs or hypnograms are analyzed, this appears not to be true. A great proportion of parents will go to any length to make their baby sleep through the night. All too often, parental convenience and comfort take precedence to baby's health. Many pediatricians are pretty ignorant in reference to the rules of chronobiology, which is not prominent enough in school curricula. Some acclaimed methods are plain scary. The cry-it-out method must have been inspired by Pavlov's methods in conditioning dogs. There is little doubt that prolonged crying and stress will inhibit baby's development. For example, if prolonged crying correlates with later cognitive deficits, it is, at least to a degree, related to the impact of stress on development (Rao et al. 2004[43]). In the end, Ferber's method seems to serve the parent, not the child. No parent's heart should stand baby's cry, esp. that it is entirely unnecessary.

Sleeping throughout the night It takes roughly 1-2 months for the baby sleep to align into a rudimentary circadian pattern. This means that initially a newborn baby does not see much difference between the night and the day! Consolidation of the fasting-associated wakefulness precedes that of the breastfeeding rhythm due to high feeding demands in the first few weeks of life (Odaa et al. 2008[44]).

An exemplary circadian graph of homeostatic and circadian sleep preferences in the first 2 months of life. The average length of unconsolidated sleep episode (red line, left vertical number line) varies from 0.5 hour at 4 pm to 1.5 hours at 9 pm. There is a slight circadian preference for initiating sleep in the early evening hours (6.2% at 5 pm)(blue line, right vertical number line) as opposed to the morning (below 3% at 6-7 am). Using various sleep consolidation methods (i.e. methods for adding up episodes that follow in a short succession), the preference for the evening sleep may be shown to be more pronounced.

Your baby may redistribute its sleep episodes equally in the day and in the night. For an ever-sleepy mother, it can lead to the illusion that the baby stubbornly tends to sleep during the day, and just keeps crying throughout the night. No wonder that many moms keep asking: What am I doing wrong?, How can I make my baby sleep in the night? The short answer is: nothing (unless there is an organic cause disrupting sleep)! Sleep in short 1-4h bursts throughout the 24 hour period is normal in newborns, and nothing can be done about it! Efforts to make a baby sleep through the night in its first months are a waste of time! Moreover, whatever parents try to accomplish that goal is likely to be harmful for the baby. In the exemplary sleep log below, we can see how the chaos of the first months slowly consolidates into a sleep pattern with a major nocturnal sleep episode and several naps during the day. Around five months of age, a pretty consistent pattern emerges with two daytime naps on most of days. Finally, at around one year old, an adult-like biphasic rhythm develops. The breakthrough usually comes when parents, unaware of the consolidation process, realize that the baby does not want to take the early nap and soon put the kid to sleep only once per day. Multiple naps during the day, at this stage, are often a result of health problems, missing some of the night sleep (e.g. due to early waking for infant nursery), bad "baby sleep management" (i.e. mostly not responding to baby sleep signals), or temporary variations resulting from lifestyle changes (e.g. travel, exhausting play, meeting people, etc.). Unless the infant clearly demands multiple naps, a single siesta nap after passing the age of 12-16 months is probably a pretty safe bet. Some parents try to push the kid to stay awake throughout the day to ensure a more solid nighttime sleep. However, sticking to child's natural preference is always a safer option.

An exemplary free running sleep log in the first year of life

Interestingly, in the presented graph there is a 3 months old long period in which the infant tends to go to sleep very late. Such a sleep pattern may be a worrying prelude to future developmental, psychological or sleep problems. However, in this case it might have as well been explained by lesser resetting impact of morning sunlight in winter months. Spectral analysis of sleep in the first months shows that baby circadian cycle might possibly be quadriphasic with constituent frequencies getting damped over time to develop a typical biphasic rhythm with a major nighttime and a minor daytime crests. For another example of the crystallization of the circadian cycle, see this one father's effort to map the regularities in his baby's sleep. This particular chart begins at a stage when the baby is primarily nocturnal, but still diurnally polyphasic (4th month). Around the 10th month, daytime napping consolidates showing a quadriphasic mode with nocturnal "naps" consolidated into a single long night-time sleep episode. Finally, around the 16th month, the child develops a crisp biphasic pattern. That transition to the biphasic mode might have been delayed somewhat by parental decisions that often determine infant's sleep slots.

Parental decisions as to the timing of sleep will largely determine the baby sleep pattern. This is why the understanding of the natural development of the circadian cycle and responding to natural baby sleep signals is vital for healthy baby sleep!

Development of a healthy circadian cycle There are two main factors that will affect the development of a healthy circadian pattern in a baby:

Exposure to the natural 24-hour cycle of daylight and darkness, and all the associated daily routines. Exposure to mother's circadian routines, amplified by co-sleeping

In many animals, the development and the initial entrainment of the circadian cycle is primarily dependent on the interaction with the feeding mother (Rivkees et al. 1988[45]). Co-sleeping should assist in the development of a healthy circadian cycle. Mother's presence in bed as well as breastfeeding can both act as powerful cues. They act as both PRC-related and PRC-independent zeitgebers (see: Phase response curve (PRC)). This means that co-sleeping will affect the sleep phase as well as the degree of nocturnal awakening and total sleep. In addition to sensory cues, breastfeeding plays also a hormonal role as the circadian cycle of tryptophan in breast milk correlates with the levels of melatonin in the child's blood (as evidenced by 6-sulfatoxymelatonin in urine; Cubero et al. 2005[46]). This naturally calls into question the practise of collecting expressed milk for later use. The development of a healthy sleep-wake cycle will naturally also depend on the fact whether the mom herself applies the adequate principles of sleep hygiene. Millions of children are forced to sleep alone in their cots. This practise is so widespread in the industrialized nations that we may safely conclude that it does not irreversibly ruin the baby's circadian cycle, but, theoretically, it might underlie the epidemic of sleep disorders in modern societies. In addition to the postnatal period, mother's circadian cycles exert their impact on the baby's brain already in pregnancy. This adds to the utmost importance of sleep hygiene in gestation. It remains controversial if nighttime exposure to artificial light can slow down or disrupt the process of the circadian cycle development. Research on the impact of light on the development of the SCN suggests that it is possible to change rhythmicity or sensitivity to light of the body clock. The changes occurring in the course of development might affect the properties of the clock for a lifetime. However, it is also possible that lifestyle can reverse or magnify those changes. The development of the SCN has been studied in many animals and results differ. For example, rat SCN periodicity develops in utero (Altman and Bayer 1978[47]), while the sleep-wake cycle in the SCN in an opossum develops in the first 3 postnatal weeks (Rivkees et al. 1988[45]). The shape of the phase response curve, which lays at the root of sleep phase disorders, may actually be influenced by illumination conditions during the development, at least in cockroaches (Page 1991[48])[graph: http://www.cas.vanderbilt.edu/johnsonlab/prcatlas/carltext/figure3.htm]. Whatever the impact of light and locomotor activity in babies, until we know more, we should always aim at minimizing nighttime exposure to artificial light, and to minimize its luminance. Despite the usual claims to the contrary, nighttime play might actually accelerate the return to sleep as long as the emphasis is put on physical as opposed to the emotional. However, as motor activity is also able to phase shift the circadian cycle, nighttime play on demand should probably be minimized. For more more see: Polyphasic sleep in babies

Co-sleeping as a circadian solution The process of maturing the circadian rhythm is neural and largely beyond parental control. However, the entrainment of mom's and baby's cycles is essential, and may determine the ultimate outcome of the process. Newborns are driven to sleep homeostatically, and woken up primarily by their feeding needs. Factors such as temperature, hunger, play, lighting, social interaction, etc. only add complexity to the picture. With a number of hard-to-predict factors that affect sleep needs, babies should always sleep on demand. If they want to play, the play should not be denied. All scheduling in their life should be done around their sleep. This basically means there are only two practicable solutions to newborn's good sleep:

Recommended (McKenna et al. 2005[49]): Mom and the baby sleep together. A mom needs to learn to adapt to periodic breastfeeding throughout the night. Mom's sleep will suffer a bit. However, with a bit of practice, breastfeeding can be minimally disruptive, and actually act as a soporific for both the baby and the mom. In other words, after a short breastfeeding session, both the mom and the baby should quickly fall asleep contented with the job well-done. Even though the development of the circadian cycle should proceed regardless, co-sleeping should assist that vital biological process. Baby safety issues related to sleeping together must be addressed beforehand (you can google for that in minutes; example 1, example 2). Even a strong one year old can be suffocated easily. If you believe your power baby will scream or wriggle, it is not true! When its chest is compressed or breathing passages get obstructed, a baby will nearly instantly lose strength and be unable to defend itself! This is why safety is paramount. For a healthy and vigilant mother, statistics are good. A bit of anxiety at the start is unavoidable and perhaps good to develop healthy and safe sleeping habits. Psychologists, behaviorists and all open-minded pediatricians will all admit that the night-time bonding is great for baby's brain development. Perfect formula for both the mom and the child. Emergency: Parental care in shifts with the help of breast milk. It may happen that for health reasons, the mom and the baby should sleep separately for a while. In such cases both parents can still get excellent sleep if they adapt to a variant of shift-work with the help of chronotherapy. For example, one of the parents chronobiologically adapts to sleeping in the 7 pm - 1 am bracket, while the other takes the 1 am - 7 am shift. In the period when the mom is asleep, breast milk, extracted in advance (or formula) can be used instead of breastfeeding to avoid major disruptions to mom's sleep (remember that milk properties also change along the sleep-wake cycle). If that solution is not feasible for any reason parents will probably need to choose between:

their own good sleep, and employing a nighttime nanny.

Needless to say, baby's sleep should never be at stake here. Sleep is vital for adult health. However, for a baby it is literally a matter of life and death as sleep disruption will have an effect on many causes of newborn mortality.

Best timing for feeding Unless specifically indicated by a qualified pediatrician for specific health reasons, feeding "on the clock" should be banished. Never wake your baby up for feeding! Feeding on demand is baby's best option! One of the cardinal sins of parenthood is overfeeding!

It is easy to observe that after a hefty dose of formula sucked down in a hurry, babies get drowsy for reasons that have little to do with actual sleepiness. It may then be tempting to feed the baby to sleep. Such a practice is bad for baby's health and will not help him or her sleep overnight. It may only assist a short-lasting sleep that will clear the homeostatic sleepiness and make baby even less sleepy than before feeding. Another reason for overfeeding is mom's convenience. In hope of getting some more uninterrupted sleep, mom will feed a baby extra formula before the night or during a nighttime feeding session. Again, parent's convenience may be harmful for the child!

Child's own bed The American Academy of Pediatrics has amazingly come up against co-sleeping! Many moms will swear their babies can sleep alone in a cot without any distress. And yet most behaviorists and anthropologists will agree: the mom and the baby should sleep in close contact as it has been practised by the human race for millennia, and by nesting mammals for millions of years. There could be exceptions on health or safety grounds. However, for an average mom, sleeping with the baby should be a pleasure, a privilege and a duty. The young mom only needs to read about basic safety measures. For a baby, sleeping with the mom should be a basic human right! Many pediatricians, nurses, midwives and "old school" grandmas will still insist that the baby should sleep it its own bed for safety, discipline or convenience reasons. You may hear a medical professional advise: "Don't reward the baby! You are making a rod for your own back". This is very surprising in the light of the fact that baby reward system is pretty well tuned to satisfying its biological needs. An average adult with a number of control mechanisms messed up by the modern lifestyle should often be denied its rewards (a fat doughnut, a morning shot of whiskey, etc.). However, all natural rewards should be considered biologically advantageous for a baby. As for the safety issues, babies do die when sleeping with moms in soft beds, due to alcohol, etc. They do so too when sleeping alone. Simple preventive measures dramatically reduce the risks of the dreaded mishap. The idea that we should train up a child to sleep alone from birth is hard to uproot. One needs to look closely at the biology of breastfeeding and baby sleep to quickly realize that training up at that stage amounts to little less than cruelty (except for cases and moments where the baby does not seem to object sleeping in a cot or in mom's absence from the common bed). A little baby is basically a feeding, growing and learning machine. All its inborn reflexes are targetted at ensuring safety, growth and brain development. The reflexes involved in rooting, sucking and breastfeeding belong to the strongest drives in a little baby. A whole series of brain centers is involved and there is a close relationship between these centers, sleep centers, and the sense of well-being and pleasure. Even though the complexity of the mechanisms involved is far from being revealed to our understanding, denying a baby mom's breast and closeness is bound to have long-term developmental consequences. Metaphorically, you could try to put yourself in baby's boots by trying to sleep naked on cold concrete with horror movies blasting loud throughout the night. I might be overly dramatic here. If a baby goes to sleep on its own without much ado, its proximity craving is definitely not as powerful as described here. However, when a baby's growth is at stake, you should always err on the safe side. This is why it makes sense to assume the worst case scenario. I would not be surprised, if over time researchers discovered a need to extend the two-process model of sleep propensity in babies by a factor involved in breastfeeding. It has been shown that a tit is a soporific. I would not be surprised if it worked as an integral contributor to baby's homeostatic sleep propensity, or even a homeostatic trigger, esp. at time where the circadian cycle is not yet fully expressed. Needless to say, babies need sleep even more than adults. The degree of neural growth, network remodelling and learning in a young brain is staggering. Both NREM and REM sleep components are essential in that process. Changing the sleep structure will affect neurogenesis (Stryker et al. 2001[10]). In other words, any form of stress before or during sleep will affect baby's brain growth. This is why baby's sleep should be the zone of highest protection. Training up to sleep alone can wait. Piglets weaned early have been shown to suffer damage to their hippocampus that results in personality changes, fear of exploration, and low stress tolerance. Many parents oppose attachment parenting as too expensive timewise. It is hard to argue with someone who needs to choose between feeding the family and behavioristically correct approaches. Here again, modern lifestyle encroaches on human biology in a vicious cycle of long-term consequences in which babies brought up using an assembly line approach are emotionally and intellectually less likely to stand up to challenges of reconciling technological and societal progress with the needs of the human body and brain. For more see: Is sleeping with my baby safe? (McKenna 1995[50]) and The Science of Attachment Parenting.

What about the mom? Is co-sleeping good for the mom? I believe everyone should taste the blessings of free running sleep. However, some of my good sleep advocacy needs to take an exception here as mom's health takes a secondary importance where baby sleep is at stake. Every mother is equipped with hidden or overt instincts that should make the experience of co-sleeping pleasurable. Naturally, in the modern world, stress, mobile phones, TV, Internet, rat race, and other factors can make it very hard. If a mom claims "I hate breastfeeding", or "I cannot sleep with my baby", she should start from a thorough examination of her own life. Breastfeeding and co-sleeping can be very rewarding if the household is sufficiently sheltered from the storms raging outdoors.

Why babies sleep so much? Do babies sleep so much because they're learning so much or are they learning so much because they are getting so much sleep? Babies sleep so much because their brains have been designed to do so in the first months of their life. They do learn a lot, and learning does increase the demand for sleep, but this is not the main regulatory factor. Sleep control systems in babies simply work differently, and you probably would not be able to make babies sleep less by making them learn less. On the other hand, long bouts of sleep are used to reorganize neural networks in the brain. In short, sleep helps learning, learning induces sleep, but the whole sleep sequence is a direct outcome of genetically programmed properties of a young sleep control system. Considering the fact that babies spend around 50% of their sleep time in the REM phase (as compared to around 20% for adults), one of the theories says that even when babies do not learn much during the day while exploring their surroundings, that function is filled up by the exploratory function of the REM sleep which helps them discover new properties and rules in things they have learned thus far. You will often hear that newborns sleep most of the time. Actual measurements may show that babies are more likely to sleep through just half of their days, while spending only a small proportion of that in deeper stages of NREM sleep.

An exemplary SleepChart log of sleep in the first month of life. Sum total of all sleep blocks is displayed on the right and averages to slightly above 10 hours per day with substantial day-to-day variations reflecting the impact of rich homeostatic input changes such as a walk, family visit, diaper rash episode, formula supplementation, etc.

Conclusion: Perfect formula for baby sleep Babies sleep best if they sleep on demand and if they are fed on demand! All forms of artificial intervention in those homeostatically-regulated patterns should be considered potentially harmful. It is helpful to spot regularities and pay extra attention to baby signals at his or her preferred feeding and sleep times, however, it is the baby's needs that should determine the actual timing. As sleep is vital for the development of neural structures in the growing brain (Stryker et al. 2001[10]), any form of intervention and artificial control should be considered potentially harmful in the long-term.

If you want your baby to be smart and healthy, let it play on demand, feed on demand, and sleep on demand.

Insomnia

Insomnia is a difficulty in falling asleep or in staying asleep. Psychophysiological insomnia can often persist for years, and result in untold damage to a person's life. Those who are desperate enough to visit a doctor are often prescribed slipping pills that are usually not much better than insomnia itself! The good news is that in most cases insomnia can be remedied easily with a sleep phase adjustment as described below. Bad news is that such an adjustment may be incompatible with one's desired work or school schedule. Half of the population in the industrialized nations has problems with falling asleep! This is called a sleep onset insomnia. Except for various underlying organic reasons, the overwhelming majority of cases of sleep onset insomnia result from the inability to entrain one's sleep hours to match the desired waking time. In other words, most of otherwise healthy people who cannot fall asleep in the evening suffer from the combination of two chief factors:

going to sleep too early in reference to their natural circadian cycle suffering from the associated stress: if I do not fall asleep immediately, I will be totally wasted in the morning

If the same people were allowed to sleep as much as they wanted and go to sleep only then when they are really tired (perhaps 2-5 hours later), in a vast majority of cases, the problem would not exist! Some scientists speak of insomnia as the inhibition of de-arousal processes. In sleep phase problems, the problem of de-arousal does not exist! De-arousal proceeds correctly. It simply proceeds at a later phase. For the young studying population, the sleep phase problem is the most frequent cause of insomnia. For students who need to get up for school early, their sleep phase is often positioned too late in reference to the desired waking hour. In other words, the optimum sleep time comes too late. Sleepiness arrives too late, and natural waking comes later by the same degree. Such a student will always battle with sleep deprivation when going to sleep late, or a degree of insomnia when going to sleep early. In that sense, there is a physical/biological underlying cause. However, as sleep deprivation is pretty unpleasant, a student may try to go to sleep early (to ensure the night is long enough), but be unable to fall asleep due to the early circadian hour. If this occurs again and again, a psychological component may compound the original problem of insomnia. The recurring sleep deprivation will produce a fear of not falling asleep in time and making things even worse. In other words, in a vast majority of cases the problem is both biological and psychological. The only true remedy is to go to sleep later and wake up later thus being late for school (almost certainly a lesser evil given some understanding on the part of the educators). The only natural half-remedy is to measure as precisely as possible the optimum time of going to sleep, and sticking to that time religiously every day. That optimum time is the earliest time that roughly provides 95% or more certainty that sleep latency will be less than 10-15 min. (i.e. no more than a quarter of an hour of tossing and turning). Very often, this optimum time will provide for a mere 4-6 hours of sleep. However, this sleep is most likely to be the best quality sleep achievable in such conditions. Naturally, affected individuals will suffer a degree of sleep deprivation on a daily basis. This is still better than futile tossing and turning, waste of time, and fitful sleep associated with insomnia. If you suffer from sleep onset insomnia, and you suspect it could be caused by DSPS, you could research additional remedies such as morning sports, strong morning lights, evening melatonin, and radical solutions such as ... giving up electricity after 19:00. Another type of insomnia, nocturnal awakening, is also often related to going to sleep at a wrong time. People who need to get up earlier than indicated by their body clock, often try to compensate for the short night by going to sleep early. If they succeed in falling asleep, they will often experience premature awakening that is nearly always accompanied by a difficulty of re-initiating sleep. If the same people were allowed to go to sleep only then when they were really tired (perhaps 2-5 hours later), the problem would likely not exist! If you wake up often during the night, you should identify and eliminate possible reasons, esp. if you appear to wake up tired. The reasons and the way to diagnose them are too many to describe. However, you should always start from the simplest one: problem with the circadian phase. In simple words, the timing of your sleep may be wrong. Partitioning of sleep is a typical symptom of going to sleep too early. If you are healthy, in free running sleep, you will rarely wake up during the night, and if you do, you will fall back asleep fast, and if you won't be able to, the reasons will be quite obvious such as: stress, noise, thirst, cold, full bladder, etc. However, if you attempt to regulate the timing of your sleep, the partitioning of sleep (i.e. interrupted sleep) will be a frequent result. It is possible to push your sleep slightly ahead or back (e.g. 15-25 minutes per day) without this negative outcome. However, once you try to push too hard (e.g. more than an hour per day), partitioning is almost inevitable. If you push backwards (i.e. going to sleep earlier and earlier), you will likely wake up early in the night, i.e. before your circadian low ensures deep sleep. On the other hand, if you push forward (i.e. going to sleep later and later), your circadian low will end before you complete your sleep cycle. As a result, you will often wake up earlier than expected. If this waking up happens very early (when you push ahead very hard), you will be tired enough to fall asleep again. In other words, whichever way you push your sleep, it will not be properly aligned with your circadian rhythm. You will then wake up early or late in the sleep cycle depending on at which end the misalignment occurs. In a vast majority of cases, waking up problem can be resolved by going to sleep at the time when your body calls for it. The solution for most of cases of sleep onset insomnia and nocturnal awakening is: Go to sleep only when you are truly sleepy! Amazingly, most people do not care to listen to their body. Many struggle with sleepiness to get more life in the evening. Others force themselves to bed long before their optimum bedtime and then toss and turn for hours. This premature landing in bed is at the root of the epidemic of insomnia (even though the official figures put circadian disorders at only 10% amongst the causes of insomnia). The only sensible and healthy time to go to sleep is when you feel you start getting sleepy. If this natural time is outrageously late, see Curing DSPS and insomnia. Early waking is also a problem for a large number of people. Those people may suffer from the ASPS syndrome. In their case, going to sleep earlier will often be a sufficient remedy. If you happen to wake up early in the morning, your further sleep decision should probably be made on the basis of how fast you believe you would be able to fall asleep. If you do not think the sleep is coming soon, it is definitely better to get up and do some work. This way you will gain in three ways:

get tired and sleepy faster (work is more likely to make you tired again) you will not get anxious about falling back to sleep as soon as possible you will not waste time on futile tossing and turning

Insomnia vs. electricity Insomnia has reached epidemic proportions since the advent of electric lighting. See how lifetime costs of insomnia match the degree of industrialization.

no data less than 25 25–30.25 30.25–36 36–41.5 41.5–47 47–52.5 52.5–58 58–63.5 63.5–69 69–74.5 74.5–80 more than 80

Disability-adjusted life year for insomnia per 100,000 inhabitants in 2002

How to fall asleep faster? There are tons of lengthy books written about sleep onset insomnia and there are a zillion tricks that people use to be sure they fall asleep "in time". The sad truth is that all those tricks only fight the inevitable: the natural sleep mechanism. They are based on slowing down the brain at the time when the brain simply does not want to slow down. Yet these tricks rather tend to blow the problem of insomnia out of proportion by adding to the sleeper's stress: so much effort, so many tricks in use, and it still does not work... I will probably just have to live with this scourge for ever! If you follow a conventional insomnia advice (see an example), you will quickly realize that most measures work great at the beginning, and then, when the placebo effect wears off, you are back to square one. Some hotels offer $1000 per night services in curing insomnia in jetlaggers. All those services are a big waste of time and money. Without a phase adjustment, insomnia will persist. It can only be masked for a while. Here is some typical unworkable advice that you may get from your sleep "expert" or from your grandma:

Ineffective! Count sheep - this is nothing else than trying to slow neural firing in the brain. This will often work but there is an increased risk of waking up after 20-60 minutes of sleep. As a result, the chances for early slumber may be gone for good. The slowdown in firing can come naturally. However, it can only come at the right circadian time which may be 2-5 hours later than you would want Ineffective! Thought dispersion - by trying to "think about nothing" you can indeed increase the chances of falling asleep; however, this may be of value only in a short period that precedes the ascending circadian sleep propensity slope. If you try it early, you will likely hover in a superficial sleep with substantial chances of awakening spontaneously. It is the circadian sleepiness that stands for your ability to maintain sleep Ineffective! Cut down on sleep - this has some power to reset the circadian cycle, however, you will feel more tired, your cognitive powers will drop, your insomniac's stress factor will triple, and most of all... your creative brain will not benefit from the last REM-rich hours of sleep! Cutting down on sleep may be an unavoidable solution among those who experience DSPS and cannot free run their sleep Harmful! Sleeping pills (esp. benzodiazepines) - pills change the sleep physiology and may affect the quality of sleep. As they often have little impact on modifying the actual circadian cycle, they can quickly become a serious addiction. Additionally, they affect short-term memory and the reaction time. Sleeping pills are a major enemy of a creative individual! Ineffective! Warm bath, quiet room, rituals, cup of cocoa, etc. - all these work to reduce the stress factor and slow down the brain. However, again that won't work well if you try it too early in reference to the circadian cycle Ineffective! Drink milk or eat turkey (tryptophan is used in the synthesis of melatonin) - this is again a method for a mild slow down with negligible effectiveness Ineffective! Take vitamins - vitamins or minerals are a standard plug for whenever something goes wrong with health. For many people, the first question is "perhaps I do not get enough vitamins?" Doubling up on the recommended dose is what often follows. A healthy diet should rarely require supplementation! Ineffective! Do not nap - well-timed short naps have little influence on the circadian cycle and not napping may only have a residual homeostatic influence at the cost of evening alertness. It may help slightly but will not solve the problem. Naps should be avoided only at times of major circadian misalignment when the body starts losing track of time and circadian variables start oscillating out of synchrony Ineffective! Avoid caffeine - when taken in the morning in reasonable quantities, caffeine should have negligible effect on the quality of sleep. When you are really tired, it is really hard to prevent sleep with coffee. Naturally, giving up the addiction (gradually!) will help a bit and won't do any harm. However, it will never be a solution! Ineffective! Herbs, meditation, yoga, aromatherapy, acupuncture, chamomile, relaxation, massage, magnesium, ... - ... the list is virtually endless!

Few things can produce as much wasted time in highly effective people as trying to fall asleep at a time when your body does not want to! Do not listen to sleep advice based solely on methods for slowing down in the evening or making you mentally or physically tired! Do not go to bed until your body slows down on its own! Go to bed only then when you are really sleepy!

The question posed in the present headline was intentionally provocative. You cannot fall asleep faster, but you can fall asleep fast. All you need to do is to wait for the right time. Instead of trying to fall asleep faster, go to sleep later, and fall asleep fast.

Phase-shift based insomnia In most cases, the real culprit in insomnia is the relationship of your working hours vs. the circadian rhythm! This is magnified manifold by the associated stress factor. For many, insomnia produces an unsolvable vicious circle that just has to be lived with. However, everyone with a chance for a flex-time work system or telecommuting should realize that the greatest benefit of these may come from increased productivity as a result of better sleep that complies with natural body rhythms. A very specific degree of morning misery is needed to reset the clock sufficiently in people with DSPS. In the equilibrium state in which misery is sufficient to keep a regular schedule, the whole night sleep is cut substantially. Daily sleep deficit and daily struggle with tiredness result. In such circumstances, it is best to go to sleep only shortly before the expected sleep hour! This way you can reduce stress, on one hand, and help your homeostatic component on the other (by making yourself tired for sleep). Dr Kripke (see a critical chapter on short sleep) says: "The false belief that people generally need eight hours of sleep is one of the common causes of insomnia. Spending less time in bed is an important solution for many with insomnia". That statement is only partly true. Indeed, trying to get 8 hours of sleep by going to sleep earlier will backfire. It is better to get less sleep when it is initiated in the right phase than to force extra hours prematurely. However, the key is not in sleeping less, but in sleeping at the right time! If you sleep in the right phase and do not need to get up early in the morning, you might actually get your eight hours with zero risk of insomnia. If you cannot free run your sleep make your morning misery as regular as possible to reach the equilibrium state. Once you know the equilibrium, stick to your standard bedtime hour. Morning misery solution should only be used as a last resort! There remains the question of weekends. Many people catch up on lost sleep during weekends. This naturally unbalances the system and results in the Monday Morning Blues. Sleeping it out on weekends, you should weigh up your pros and cons:

on one hand, you entrain your sleeping cycle to later hours and make it harder to stick to your misery equilibrium on the other, this is your only chance for quality sleep

There is no simple answer to the weekend dilemma! If you want to maximize the effects of sleep on learning, skills and experience, you would need to quantify how much you lose as a result on never actually getting enough sleep (the losses could be dramatic!) and how much you lose as a result of departing from the misery equilibrium on weekends thus tripling sleep disturbances early in the week.

For healthy people, the most effective solution for persistent insomnia or work-schedule-related sleep deprivation is free running sleep!

Free running sleep is simple to define, but a bit harder to execute for beginners. It will often conflict with one's expectations and needs as to the timing of sleep. You will know that free running sleep worked for you if you replace insomnia with no more than 3-5 min. in bed before you fall asleep (without medication).

In healthy people, the time to fall asleep should not be longer than 5 min!

If you succeed with free running sleep and discover that you can fall asleep in 5 min. as long as you go to sleep at your natural hour, you may discover a new problem. You might show a tendency to wake up later each day. If this is the case read: Curing DSPS and insomnia.

Hypersomnia

Hypersomnia is excessive sleepiness in conditions of getting physiologically sufficient sleep. Hypersomnia may be related to serious health problems. However, if you keep battling drowsiness, your problem does not need to have a serious organic cause. There is a simple home-grown diagnostic method that can help you eliminate a frequent and less severe cause: a phase shift disorder. Try to free run your sleep for a few weeks. Very often, the phase adjustment will resolve perpetual tiredness! Quite frequently, sleep initiated too early in reference to the circadian sleepiness will last very long and paradoxically result in the feeling of not being refreshed in the morning. If the subjective circadian night period overlaps with the actual waking time, you may experience overwhelming drowsiness, yet you will not be able to fall asleep for longer than 20-30 minutes and you will still wake up unrefreshed. Even buckets of coffee may not help in such circumstances. If you do not notice a significant improvement in the quality of sleep after 1-2 weeks of free running sleep, you may suffer from an underlying health problem that will require a professional consultation. See: Sleep and Hypersomnia at WebMD. A frequent cause of poor quality sleep is Obstructive Sleep Apnea (OSA). OSA is caused by breathing difficulties during sleep (see the next section).

Sleep apnea

Sleep apnea is a problem with breathing during sleep. In all cases of getting unrefreshing sleep despite adhering to all the rules of sleep hygiene (esp. in free running sleep), sleep apnea needs to be ruled out. An initial home-made diagnosis may be made by a bed partner or by video-taping one's own sleep. All pauses in breathing or heavy snoring should be worrisome and consulted with a sleep expert. The most frequent type of sleep apnea is the obstructive sleep apnea(OSA), which affects up to 10% of male population (it is about half as frequent in women). OSA involves a loss of muscle tone in the throat and tongue areas. These structures tend to collapse during sleep and block the flow of air. As a result, the patient will wake up temporarily (often a hundred times in a single night) without completing the natural NREM-REM cycle. Patients with OSA wake up feeling unrefreshed. You can also videotape yourself when sleeping. Most often, OSA affects obese and heavily-snoring males. There are multiple support sites for OSA on the web (including recordings of snoring patients and typical signs of interrupted breathing). Sleep apnea needs to be treated with urgency. It undermines one's cognitive powers in a short-run (due to its effects on the quality of sleep) and in a long-run (due to its negative effects on brain growth and aging). If anyone tells you that you snore heavily, do not treat is as a natural thing: "my uncle also snores like a tractor and seems to be ok". All cases of snoring should be investigated. Snoring may be a first sign that your brain is not getting what it needs during the night sleep! Sleep apnea can also lead to cardiovascular disorders, depression and a whole host of negative health consequences. One of the best natural weapons against sleep apnea is weight loss by combining a healthy diet and exercise. Exercise on its own may also be helpful as long as it is chosen carefully to make sure it does not exacerbate snoring (e.g. through nasal congestion).

Napping

Napping is good

The natural sleep-wake cycle makes you feel less alert in mid-day. This period can easily be visualized using EEG measurements. In many tropical, subtropical, and Mediterranean countries this is the time for siesta. The drop in alertness can be magnified by a rich meal and a short nap is likely to quickly restore full alertness. However, the industrial nations do not seem ready to adopt the healthy habit of a postprandial nap. Just the opposite, when the Mexican parliament debated the law on statutory napping, politicians and comedians north of the border had a good laugh about "lazy Latin Americans". Siesta Awareness in the UK abruptly cancelled their National Siesta Day 2009 upon a publication from China that showed that diabetics nap more. Myths galore. Napping is smart, and yet nappers are often considered lazy, or weak. The self-improvement guru, Tony Robbins, provides a typical misguided get-up-and-go advice on napping: replace a nap urge with press-ups. Press ups will improve circulation and raise the level of catecholamines. This will make you feel more alert for a moment. However, only a nap can provide a true neural boost to your cognitive powers. Nap is better than exercise. Nap is better than caffeine. Nap is irreplaceable.

Napping and evolution There are few theories on the evolutionary purpose of the mid-day dip in alertness. Most people believe that humans, as all other highly developed tropical animals, have developed a siesta habit as a way of getting around the midday heat. This explanation has also some cultural background as napping is by far less popular in moderate and cold climates. However, the alertness dip can be resolved by a short nap in minutes. This can make us active again long before the mid-day heat is over. Another explanation is that the alertness dip is an atavistic remainder of the polyphasic sleeping mode that might have characterized human ancestors. Many animals and newborn babies sleep many times during the day. This might seem advantageous for optimizing memory circuits. However, consolidating sleep into a single night rest period might have offered some evolutionary advantage too. Early humans might have been less efficient in hunting and gathering activities at nighttime. This is why it might be advantageous to spend nights on memory optimization. Possibly, the consolidation of sleep went gradually from polyphasic sleep, through biphasic sleep to semi-monophasic sleep in modern humans. Actually, similar consolidation can be observed as we get older. By the time of adulthood we are more or less monophasic with a clear dip in alertness that may be resolved with a short nap. As we near retirement, we again seem to tend to become biphasic. This may be a result of the fact that working people are forced to suppress their biphasic tendency. We remain strongly biphasic throughout the lifetime, and the monophasic model has largely been imposed by industrialization. When I look at learning performance data collected with SuperMemo, I see that the homeostatic decline in cognitive powers throughout the day is steep enough to provide an alternative explanation: nap is cognitively beneficial, but not essential enough to boost it with a full-swing circadian support. As a result, we have developed a half-way sleep system that ensures the essential fully blown nighttime sleep, and a window for an optional mid-day alertness booster. As the circadian component of sleep drive is associated with some physiological functions of sleep, a system with homeostatic napping might not have been equally beneficial. As for the speed of homeostatic decline in alertness, it could be inherent to the networks involved and might depend on energy reserves, supply of neurotransmitters, size of the networks involved, etc. It should also depend on the degree of use. The heavier the mental effort, the faster the decline in cognitive performance. In other words, for the brain as it is, and for heavy mental loads, slower homeostatic decline may simply not be physically possible. The timing of the mid-day nap comes from the fact that splitting the day into two exact halves maximizes overall alertness. Here again, mid-day tropical heat might actually provide an additional evolutionary incentive.

Naps and brain power The father of the napping science, Dr. D. F. Dinges has spent many years investigating the problem of alertness at workplace and has shown substantial benefits of napping in professions where the alertness may be the difference between life and death. His research showed a substantial alertness boost coming from a nap (Dinges 1989[23]). He has also noticed relatively little impact of napping on the night-time sleep in regular nappers:

However, when Dr Matthew Walker published his research proving the value of napping for cognition (Walker and Stickgold 2005[51]; Walker and Nishida 2007[52]). Professor Derk-Jan Dijk commented surprisingly: "there was no clear evidence that daytime napping offered a distinct advantage over sleeping just once over 24 hours (...) while the brain effect reported in the study might be spotted in a laboratory setting, the picture became more clouded in the "real world"". Today, you can measure the benefits on napping on your own using SuperMemo. Comparing recall graphs of nappers and non-nappers, we can clearly see how non-nappers power at half-steam through the second half of their waking day (see: Biphasic nature of human sleep). Dr Walker, who confirmed his point with later research, says convincingly: "It's as though the e-mail inbox in your hippocampus is full, and, until you sleep and clear out all those fact e-mails, you're not going to receive any more mail". Take it from a religious napper Mr Winston Churchill: "you get two days in one"! The value of the nap increases in proportion to the degree in which your work depends on your brain and the quality of your thinking.

To nap or not to nap? Nap! Here is a short summary of pros and cons of afternoon napping: Pros:

Siesta naps, rich in NREM sleep, result in a significant increase in alertness that will be highly appreciated by people in creative professions. By various measures that boost may be as high as 50%! As shown with SleepChart, napping improves recall and memory consolidation in the second half of the day Well-timed napping may help combat sleep deprivation. Some people even prefer to sleep in two 3-4 hour portions throughout their lives! Naps reduce blood pressure, improve cardiovascular health, and might, as a result, prolong your life!

Cons:

Badly timed (late) naps may worsen insomnia. This is why so many sleep experts counter-recommend naps. However, proper timing mitigates this problem Badly timed (late) naps may result in sleep inertia. This can be resolved easily with proper nap timing. Napping requires good rest conditions, conducive napping culture, and solid napping skills and habits. All these may be hard to come by in industrialized nations.

If you ever hesitate, to nap or not to nap, take a well-timed nap and see how it impacts your life. If you wake up groggy, remember that napping is also an art. Read about best timing of naps. Chances are, napping might become a beloved habit that will increase your productivity. Many great minds napped habitually. In addition to Churchill, notable nappers included Napoleon, Bill Clinton, and J. F. Kennedy. Interestingly, this group also includes a famous long-sleeper, Albert Einstein and a famous short-sleeper Thomas Edison. Even Bill Gates enjoyed taking naps under his desk in his creative programming years.

Napping in the corporate world More and more companies in the US have already decided to make a switch from a coffee break to a napping break with special cubicles designed for nappers. In the future, this trend is likely to become more prominent as caffeine is not a fraction as effective as a nap in combating fatigue. For neural reasons, coffee, doughnuts, press-ups, and other methods taken together will never prove as efficient in mental restoration as a nap. At the same time, our society drifts strongly towards information processing where alertness is central to productivity. And when the productivity comes into the equation, corporations will definitely avail of the up-to-date research on napping. Important! Do not confuse the healthy concept of a siesta nap with a very unhealthy idea of polyphasic sleep.

Napping rulebook Do not use the alarm clock! Contrary to popular belief, well-scheduled nap will not result in sleep inertia (unless you are seriously sleep deprived). Alarm clock can seriously undermine the value of the nap! Measure exactly the optimum length of the period between the natural awakening and the nap to maximize the effectiveness of a nap. The nap should come at the nadir of alertness, which usually comes 7-8 hours from natural waking. Napping beginners often miss the right timing! Choosing 7 hours as your starting point will allow of a 60 min. margin in case you were late for one reason or another. Drink coffee or other caffeine drinks only after the nap. Even the tiniest amounts of caffeine in the system might interfere with the quality of sleep. If you drink alcohol before the nap, it should be largely metabolized (i.e. out of your system) by the time you fall asleep If you nap for more than 100 minutes, you probably need more sleep in the night (or you nap too late) Avoid stress 1-2 hours before the nap. Even things you love can make you excited and make it harder to avail of the benefits of napping Exercise is good. Try to finish your exercise at least 45 minutes before the nap. If you fail to cool down, your nap may end up prematurely Meal before the nap is recommended. Unless your doctor says otherwise, your main meal of the day should actually come before the nap (around the 6th hour of your waking day)! Sex before the nap is recommended Stick to your ritual (e.g. stick to your best sequence: exercise, beer, bath, meal, quiet place, nap, music, or similar) If the above advice does not work, you may need a month or so of trying. Mental slow-down is critical here! Many people do not discover the benefit of napping until some circumstances put them into the routine (e.g. heart condition diagnosis). Even if you cannot fall asleep, you may still need a nap! Sleeplessness may only be a result of a habit or your inability to forget the worries of the day. You may simply not fully understand your actual sleep needs. If it all won't make you fall asleep in 10 minutes even after a month of trying, you can probably safely give up napping for good

Napping myths

Myth #1: Only lazy people take naps In some cultures, this harmful myth makes people feel ashamed that they are weak enough to need a nap. This myth must be abolished promptly. Naps have a great effect on cognitive function and productivity. If you want to take a nap, take it and announce it proudly. You are doing a smart thing. Naps make you smarter! When Newt Gingrich was caught asleep on camera, commentators pointed fingers in all wrong directions: he is getting old, he is tired of the campaign, he might be suffering from Alzheimer's, etc. Gingrich was set to video-stream live via satellite hook-up to the American Israel Public Affairs Committee. During a preceding Panetta speech, he opted for a quick nap in a sitting position. His age or health did not need to have to play any role here. In fact, Newt was doing a smart thing: he was clearing up his brain before appearing before a demanding audience. However, despite a short span of time available, he managed to launch deep sleep and woke up with clear signs of sleep inertia. He did not know where he was and what he was about to do! He recovered pretty fast with stump lines attacking radical Islam. Those sleep inertia symptoms did not need to indicate he was tired of the campaign or that his sleep deprivation carried over from many days of sleep debt. Even a single night of lost sleep would be enough to put anyone in his position. His being a political old-timer worked against him. No novice would be able to overcome the stress of public sleeping to get a few zzzs. The only obvious mistake Gingrich made was to fail to get his full load of sleep on the preceding night. For more see: Why naps cause sleep inertia?

Myth #2: A nap is a nap is a nap This myth says that every nap is a good nap. It does not matter when it is taken and how long it lasts. This myth lives deep in the psyche of inexperienced nappers who often do not realize the myriad of genetic, metabolic, neural, and hormonal processes that cycle through the human body throughout the roughly 24 hour period. In the section titled Best nap timing, I include a general partitioning of the circadian cycle with a short analysis of what processes occur when a nap is taken at each selected point of the cycle. Naps taken at different points of the circadian cycles are as different as chalk from cheese. Some are refreshing. Some are a waste of time. Some may be unhealthy (or at least inefficient). Some will last several hours!

Myth #3: Make sure you wake up from Stage 2 NREM Some napping "experts" will tell you to use an alarm clock to make sure you wake up after 15-20 min from Stage 2 NREM. Supposedly, longer naps send you into deep sleep (Stage 3/4 NREM), and you wake up groggy. In reality, it is the timing of naps in reference to the circadian cycle, as well as the prior sleep deprivation and REM-sleep deficit that will determine the nap duration and the effects of the nap. On some occasions, it may happen that a nap cut short with an alarm clock will be somewhat refreshing and will prevent the ripples of a wrongly timed prolonged nap. However, it is always better to choose the appropriate time for a nap. It will usually be around 7-8th hour of the subjective day. This translates to 7-8 hours from waking in free running sleep. However, in conditions of sleep deprivation, or misaligned sleep cycle, it is safer to take an earlier nap or even skip the nap entirely to help cycle re-synchronization. Did you hear a story in which Einstein supposedly napped with a pencil to wake up as soon as the pencil dropped? I doubt a great genius would make this mistake on a regular basis. I am sure he had a chance to compare the values of a well-timed natural nap and an interrupted nap. Perhaps a pencil dropped indeed. Once? Perhaps the genius brain was thus deprived of some new creative insight? Or conversely he was inspired by an interrupted mentation? Perhaps it was just a nice story to tell over a cup of tea? Whatever the truth, do not follow this example! Let your brain decide how long the nap should last!

Myth #4: The circadian cycle can be ignored or abolished A harmful myth says that we could ignore the circadian cycle, so that the sleep can be reduced to one-dimensional homeostatic process. This myth comes from the lack of understanding of the two-process nature of sleep. It made many to believe that polyphasic sleep is a good long-term lifestyle choice. The myth comes from the lack of appreciation of the overwhelming power of the primary circadian sleep component. Consequently, the myth bears a belief that naps can be induced at will at any time that is sufficiently far away from the prior nap. Have a peek at the following amazing picture obtained with the help of SuperMemo.

The graph shows the powerfully biphasic nature of the human circadian cycle. The horizontal axis shows the circadian time, i.e. the time that elapses from phase 0, i.e. the predicted "end of the night" time. The prediction comes from the circadian model employed in SleepChart, and is derived from the sleep log collected in SuperMemo. The red line is the predicted alertness derived from the same sleep log data using the two-process model of sleep developed for the purpose of sleep optimization in SuperMemo (the model is inspired by similar work of Alexander A. Borbely and Peter Achermann). The alertness is a resultant of the status of the two sleep-drive processes:

the homeostatic process and the circadian process.

The blue dots are recall data taken from an actual learning process in SuperMemo. In other words: red is the model, blue is the data. Both tell the same story! For skeptics who do not believe in scientific models, blue-dot unprejudiced data should be the ultimate clinching argument. The graph says unequivocally that we got two major peaks of alertness during the day. It also states clearly that there are only two valleys conducive for sleep and napping.

Best nap timing

Naps are a blessing for a tired brain. However, if taken at a wrong time, they can also contribute to messing up your sleep cycle. Many people believe that a nap is a nap is a nap. Whatever its timing, the nap will refresh your mind. This is false. Understanding the optimum circadian timing of naps is essential for naps to be your friend, not your enemy! The belief in the universality of naps sparked a dangerous ideavirus: lifestyle based on polyphasic sleep. Napping is a skill. Many people cannot nap even if they are sleepy. Measuring the time between your natural waking and the nap should help you optimize the quality of a nap. Optimally, your tiredness might not even be perceptible enough to easily guess the optimum timing. If you measure the time between night sleep and the nap, you will notice that the length is always the same (minor variations depend on the quality of sleep in the night). In other words, the measurement helps you figure out the timing of your circadian dip even on days when you do not feel tired at midday. You may wonder, why nap in the first place then? The boost in cognitive powers is worth the investment (which may be as little as 10-20 min. on a good day). In a healthy biphasic sleep, a nap taken at siesta time is an excellent boost to your mental energy and creative powers. It is important to know that the timing of the nap should not be determined by the clock that hangs on your wall. Your nap should come at around 7-8 hour of your natural waking time. To be precise, only you can determine that value precisely by comparing what happens if you try to take naps a bit earlier or a bit later. The optimum value may not hold if you cut your sleep short with an alarm clock, or fall asleep earlier than usual (e.g. because of an exhausting day), or delay going to sleep beyond your natural sleep hour.

Circadian timing of naps To optimize your nap taking, you need to understand the impact of the sleep cycle phase. Below, I explain what happens if you take naps at different phases. In the text below, Phase 7 Nap denotes a nap that is taken 7 hours after natural awakening from sleep taken at natural hours. Refer to the following graph which illustrates the biphasic nature of human sleep propensity. This graph shows that there is only one optimum alertness valley (in red) conductive to sleep, usually in hours 7-8:

Phase 0: Waking time Napping in Phase 0 is napping that takes place immediately after waking, i.e. Circadian Time 0 in the graph above. Napping in Phase 0 is possible, and largely depends on the history of prior sleep. Phase 0 naps after a normal night sleep can be considered as a complement to the night sleep if it was not effective enough. Such naps consolidate with the night sleep in sleep models and are an efficient way of extending the night sleep in cases when it was interrupted (e.g. by noises, bursting bladder, health issues, etc.). Phase 0 naps after a sleepless night can serve as an inefficient substitute for the night sleep. Such sleep will be short, unrefreshing and leave a sleep debt. It will also introduce unwelcome oscillations in the circadian system that may take a few days to clear up. Such sleep is often used by night-shift workers to get some mental boost for a day. It is still far better than no sleep at all. The rule is simple: if you are sleepy at Phase 0, nap at will. Your brain clearly needs more sleep.

Phase 3: Creativity time Napping in Phase 3 should not ever be possible in a healthy well-regulated system (see the red peak in hour 3 on the horizontal axis in the graph above). Successful sleep at this time is an indication of sleep deprivation, poor quality sleep (e.g. due to sleep apnea), sleep in a wrong phase (e.g. taken too early), sleep disorder (e.g. narcolepsy), etc. This is probably the hardest time to nap of all. However, I am not aware of any bad effects of such naps for health or for sleep control systems.

Phase 5: Pre-siesta Napping in pre-siesta slot is possible. However, such naps are likely to be short and not as refreshing as Phase 7 naps. They are also more likely to be REM-rich for circadian reasons. Those early naps can probably be recommended to people who suffer from sleep-onset insomnia, and who still want to boost the second half of their day in terms of alertness and creativity. Those naps can also be executed "in a hurry" due to their short duration in cases where longer napping is undesirable, or later timing does not fit the day's schedule.

Phase 7: Siesta Perfect time for napping. As it can be seen in the graph, this is the period when the mental performance is at its mid-day nadir (aim at Phase 7 to make sure being late will still place the nap within the nadir). It is not true that the nadir is caused by a hefty lunch (even though meals have a big impact on sleep control). The nadir is a natural expression of the circadian wave. This circadian low time comes at the roughly same clock time as the subjective night nadir at a roughly 12 hour shift (e.g. if the middle of your night falls at 3 am, naps at 3 pm could be most effective). This is well explained in "How to nap". The benefits of a siesta have been confirmed by numerous studies. It has been practised for ages in many regions of the world. It will definitely trickle into the corporate world as human productivity becomes increasingly dependent on our creative powers.

Phase 11: Evening This is not a good time for napping. In a healthy cycle, napping might be hard to achieve or impossible. However, even a minor degree of sleep deprivation will produce a nap that might trigger the control mechanisms responsible for the full-night sleep. Late naps are likely to be rich in NREM sleep and rob your night sleep of the vital SWS component (Werth et al. 1996[53]). Those naps can last far longer than siesta naps. They can make you groggy. Worst of all, they can compound insomnia. Unfortunately, this is a type of a nap that a huge proportion of students take! Forced to wake up at indecently early times for school, kids and students struggle semi-conscious through school hours with negligible progress in learning. Learning in such a state only magnifies the pretty universal hatred of school. Phase 11 nap is then the only way to survive the day and get some actual learning done in the evening. The body clock shifts the subjective night to the morning hours. The positive side effect is that evenings can be filled with effective studying. The negative side effect is that the student finds it impossible to fall asleep before 3-4 am, and welcomes the new bright school day with an alarm clock that rings in the middle of the subjective night. This perpetuates the cycle of suffering and school hate. Nobody has ever estimated the global consequences of this phenomenon that includes an impact on adolescent attitudes that are notoriously fraught with problems. Neither has anyone come up with a practical solution (shifting school hours usually results in kids "adapting" to the new cycle by shifting their bed time as well). I am not able to recommend a solution here either. Skipping evening naps might be better for the quality of night sleep and for the stabilization of the circadian cycle in the earlier phase, however, that would effectively rob those students of their only time in which they can learn. Those evening naps are also the only meager substitute for free running sleep that those young brains crave. The only time when the brain gets what it wants. If I was to answer: to nap or not to nap, I would probably have to admit that evening napping is the lesser evil in a majority of cases.

Phase 13: Pre-sleep This is a particularly bad time for napping. Initiating naps at this time should be relatively easy. However, pre-sleep naps are likely to produce one of the following unwelcome outcomes: long-nap-short-night or long-night-early-waking (depending on the current status of the sleep control system). A pre-sleep nap is likely to result in triggering the night sleep sequence. However, this sequence is not unbreakable, and can result in early awakening combined with the difficulty in launching back to sleep. This is particularly likely if the homeostatic sleep process generates substantial sleepiness while the circadian process is not yet mature for the night sleep. As a result, such a pre-sleep nap can yield less total sleep than a normal night sleep. This long-nap-short-night will not entirely fulfill the physiological function of sleep. Consequently, your alertness levels for the next day are likely to dip substantially. The less unfortunate outcome of a pre-sleep nap is if you successfully trigger the uninterrupted night sleep sequence. However, you will likely prematurely run out of the homeostatic process before the circadian function of sleep is completed. You will probably wake up earlier than usual. This is the long-night-early-waking outcome that produces nights that are amazingly unrefreshing considering the fact that premature sleep is often much longer than an ordinary night sleep. The reason for this low sleep efficiency is probably the scarcity of REM sleep which is strongly circadian. Moreover, for circadian reasons, your morning is likely to be unusually sleepy!

Phase 15: Segmented sleep Phase 15 napping should be considered "early night sleep". If you go to sleep at this time you can expect any of the following (depending on the degree of sleep debt):

if you carry no sleep debt: some unproductive time in bed, as you might not be able to fall asleep. pre-sleep outcome as in Phase 13 sleep: long nap with a short night, or long night with early waking. This outcome is likely to leave you less refreshed. segmented sleep: you will fall asleep, but will wake up for 1-2 hours in the night only to fall back asleep. This lucky outcome will leave you pretty refreshed. long night: on rare occasions, esp. if you are sleep deprived, early bedtime will result in a nice long refreshing night sleep.

Due to the precarious nature of Phase 15 sleep, it should rather be employed only in conditions of sleep deprivation, which provides good chances for a positive outcome. Otherwise, early bedtime may be unproductive at best, and bad for the quality of sleep, at worst.

Phase 18-24: Night sleep If you try to nap in Phase 18-24, you are bound to trigger a normal healthy night sleep. This is ok as long as you do not get down to "napping" with the evil intent of stopping the process in 20-40 min. Here is where the pain of polyphasic sleeping becomes hardest to bear. As Dr Stampi noticed two decades ago, it is not the problem with staying awake or with falling asleep that is most exasperating. The most painful part of a polyphasic life is when your brain wants to trigger the night sleep sequence and a polyphasic adept stubbornly disallows it (Stampi 1992[54])! This is as bad an interruption as any other abrupt stop to an all-or-nothing physiological process (urination, defecation, orgasm, swallowing, heartbeat, sneezing, coughing, childbirth, and the like). Many polyphasic bloggers note: "I noticed that when my naps get longer, I get groggy. So I try to keep them under 20 min". Duh! If you do not launch the night sleep sequence, you will not suffer the pain of interruption. Why nap in the first place then? It's easier to delay defecation than to stop it in the middle. The most unusual night-time nap control method I have encountered was... "I keep lots of junk in my bed. That keeps my naps short"! Important!

The napping phase refers to the optimum natural waking time. Not the actual waking time! For example, in a premature sleep, or in an interrupted sleep, an efficient nap can take place 10 hours from waking. If your sleep is not entirely natural, you need to take a correction for your inherent circadian cycle that might be running in the background independently of your actual sleeping hours. Unfortunately, a vast majority of people with sleep phase problems have no idea how to efficiently measure and plot their natural cycle. The two alertness valleys are biologically dissimilar! As it will be shown later, only the night-time valley can produce a typical long-drawn periodic NREM-REM interplay with a gradual increase in the proportion of REM. The subjective night period is marked by a characteristic increase in the release of melatonin. The length of siesta sleep, as shown below, in the biphasic sleep graph, is 4-20 times shorter than the natural night sleep. Phase response is elicited by stimuli that precede or follow the night sleep. However, the same stimuli may affect the timing of the siesta nap, which in turn may have an indirect impact on the cycle phase. Timing of naps will determine their structure. Some researchers believe that this can also affect the efficiency of naps for a particular type of mental task due to the fact that nap timing determines the proportion of NREM to REM. This might be true if you want to maximize value/time for specific tasks. However, with sleep optimizations, you should always go for the maximum total value. This is why the best nap is a nap well aligned with your midday circadian dip in alertness.

Good conditions for a nap are important. A nap in a semi-reclining position, or in a noisy room, or in bright lights, will also bring benefits to your alertness (on condition you actually manage to fall asleep, and perhaps pass Stage 1 NREM). However, a nap in a sleep-conducive environment will often last longer and be far more refreshing.

One nap per day is enough

Many people believe that every extra successful nap can be preciously helpful in restoring their mental energy. In a normal sleeper, who is not sleep deprived, an additional nap is indeed likely to bring increased alertness and improve mental performance. However, on a healthy schedule, all naps outside the siesta period should be very hard to accomplish. If the goal of sleep is defined as achieving maximum creative productivity, and if the night sleep can run its healthy course (i.e. there is no sleep deprivation), then any nap attempt at times other than the siesta time will be wasteful. This is because falling asleep should be difficult, and simply resting with the eyes closed does not yield a fraction of the neural benefit of an actual successful nap. Moreover, even if successful, an extra nap forced in in the morning is likely to interfere with the afternoon nap. Similarly, an evening nap may result in shortening of the night sleep. Those extra naps may bring incremental improvement in performance, but will reduce the overall efficiency of sleep and may cause ripples in the circadian system. Our biphasic nature makes it quite clear, we should strive at a single nap in the afternoon (in the 7th hour of waking). For some people, even this will be too much, and monophasic pattern is their optimum. Many young creative individuals come up with their own designer sleep schedules. I often get mail with submissions of new sleep pattern propositions. For example, triphasic sleep: one main sleep episode of 6 hours (00:00-06:00) with two 30 minute naps after meals (12:00-12:30, and 18:00-18:30). Like most of artificial ways of making the sleep system work to design, this schedule is not likely to be efficient. Most people are strongly biphasic, and only biphasic or monophasic sleep works well for adults. However, if one throws away the second nap, the proposition will be pretty close to a natural biphasic rhythm: 0:00-6:00 and 13:00-14:00. Even though, designer schedules should always be avoided. The only exception is for designs that are an approximation of what SleepChart shows in free running sleep. As people differ in various parameters of their sleep control system, those who are very regular sleepers might indeed consider wiring a specific timing to their schedule as long as the timing is derived from their actual sleep pattern measurement. If sleep episodes in a designer schedule are not aligned with the circadian needs then they will often lead to a circadian chaos. If you want to sleep well and be productive, choose biphasic sleep, monophasic sleep, or free running sleep, whichever works best for you, and whichever you can afford. Free running sleep synchronized with the daylight cycle is the healthiest and will result in highest productivity. Once you run free, you will determine quickly if your prefer to sleep biphasically or monophasically.

Polyphasic sleep

The law of accelerating returns We live in the times of accelerating acceleration. The Moore's Law makes the world smaller, faster, more connected and more efficient. We are now able to touch and feel Kurzweil's generalization: the law of accelerating returns. The fast-living young generation is hungry for more. More fun, more information, more accomplishment, more education and... more waking time. It is pretty amazing to see how many people will lean over backwards to shorten their sleep to increase productivity. Young self-experimenters keep cutting sleep short with alarm clock, using controlled substances, pulling regular all-nighters, or trying to use the sleep time for "useful purposes" (e.g. learning in sleep). In a blog of a young entrepreneur attempting to save life by sleeping less, I read (boldface emphasis is mine): "Sleep is not my friend. As a budding young entrepreneur I have a desire to go about life with less sleep and more waking moments in life. I always feel like those moments in bed are moments that could be used for a more noble purpose. [...] As any good Industrial Technologist knows for something to be controllable it must be measurable. So I wrote down the time I went to sleep and time I woke up every morning for a year. Measuring it gave me a good benchmark to improve upon". A praiseworthy one-year record of measurements followed and produced a nice graph of healthy and regular sleep averaging an enviable 8 hours per night (slightly less in summertime). A sleep expert might exclaim: "Good for you! Keep it up!" But a budding entrepreneur goes on to "improve upon" millions of years of evolution. "This is a total of 112 days asleep and 253 days awake. Or, to put it another way, I slept away 31% of the year, [...] I tried a few experiments with my day to see if I could reduce the time I spent sleeping. For example, I once tried strictly limiting my sleep to 5 hours each night … it lasted about 2 weeks and I gave myself a fever. Then I tried pulling an all-nighter once a week for as many weeks as I could manage. That did not last long either. Most notably because the 2nd day after the all-nighter was always so unproductive that the extra time I was awake did not produce a net increase in my productivity. [...] I have yet to find a good way to sleep less on a consistent basis". I wonder why a good Industrial Technologist did not bother to spend 5 min. to google for the function and the noble purpose of sleep. After all, you do not need an honors degree in biology to know that if the body does something, it is nearly always for an important purpose. In addition to the said hunger for more productivity and more waking time, the myth-making power of the human mind is now grotesquely amplified by the all-mighty Internet. If there is an idea that could make life better or more bearable, it quickly takes on its own Internet life as soon as it is invented. Along the rules of the memetic science, the idea grows, mutates and evolves. It feeds freely on science as well as on rumor, self-experiment, and unscrupulous sources biased by self-interest ready to trade truth for profits. It snowballs adding new pleasing facts and hypotheses as it rumbles over the unprepared minds. Like a new messiah, it drags behind new followers, advocates, apostles and die-hard guerillas ready to contribute to the ultimate victory of the cause. Around the year 2000, a new meme cropped up in several blogs on the net: The Uberman's Sleep Schedule. Due to my interest in the role of sleep in memory and learning, it did not take long for the meme to hit my inbox. As the concept kept ballooning on a monthly basis, it left me with little choice but to take a stand.

The Uberman's Sleep Schedule The idea behind the Uberman's Sleep Schedule is to gain waking hours by sleeping the total of just 3 hours in 6 portions distributed equally throughout the day. There are many variants of the scheme proposed by those who tried to sleep along the schedule. The schedule is supposed to compress physiologically less important stages of sleep and homeostatically upregulate stages vital for mental health. The Uberman's Sleep Schedule was proposed in this blog at Everything2 by a woman hiding behind a nick PureDoxyk. The blog reported a sleep experiment with an innocent admission that the Uberman schedule was incompatible with the experimenter's schedule and goals. Yet the meme was picked up in a Kuro5hin article in 2002. Phrased in a simple and well-structured language, this time it was noticed. Again, the post ended with "Uberman's sleep schedule is a potentially dangerous way to increase your waking hours". That did not prevent a frenzy of new followers ready to gain years of waking time. The catchy theme of the concept is that, indeed, if you succeeded in sleeping 3 hours per day instead of the prescribed 8, starting at 20 years of age, you would gain over 11 years in an average Western lifespan. The idea is very attractive. No wonder then that as such it seemed to keep gaining momentum for quite a while.

Polyphasic sleep More and more frequently, Uberman's Sleep Schedule was being referred to as polyphasic sleep(the term popularized by research and book by an Italian chronobiologist Dr. Claudio Stampi). Polyphasic sleep is known to sleep researchers as a variant of a sleep pattern that is set in opposition to monophasic or biphasic sleep. In monophasic sleep, an individual or an animal sleeps in a single block during a single wake-sleep cycle of 24 hours. In natural biphasic sleep, there are two blocks of sleep in 24 hours: the night sleep and the typical Latin siesta (the "7th hour nap"). Polyphasic sleep is quite widespread in animal kingdom. In a recapitulation of phylogeny, human babies also sleep polyphasically, and gradually lose their napping propensity until they become roughly biphasic around the age of one. Human adults, as much as all great apes, are largely biphasic. Although a majority of westerners do not nap on a regular basis their alertness shows a slump in the middle of the subjective day. This slump can consolidate in a short sleep episode in free-running conditions. The theory behind the Uberman's Sleep Schedule is that with some effort, we can entrain our brain to sleep along the ancient polyphasic cycle and gain lots of waking time on the way, mostly by shedding the less important stages of sleep (e.g. shortening Stage 1 of NREM, which seems to be just a transition state to the more "useful" stages of slow-wave sleep). That theory is flawed as it does not take into the account the magnitude of the circadian acrophase in the subjective night.

To sleep or not to sleep polyphasically Having presented polyphasic sleep as seen by its enthusiastic advocates, let us have a look at its physiological roots and implications. With every passing month, we accumulate a tremendous body of evidence of the vital role the sleep plays in memory and creativity. In addition, most of us have a good understanding that without sleep there is little chance for an intellectual accomplishment. Even more, we find it hard to stay awake unassisted for longer than 2 days. Although, super-human achievements have been well documented, where people like Peter Tripp (1959), Randy Gardner (1965) and Tony Wright (2007) stayed (semi-)awake for 8, 11, and 11 days respectively, most of the mere mortals cannot even suffer through the first 48 hours of wakefulness and inevitably fall prey to slumber. EEG and actigraphy measurements indicate that humans are basically biphasic. There is a single powerful drive to sleep during a subjective night, and a single dip in alertness in the middle of the subjective day. EEG measurements are confirmed by many other physiological variables such as temperature measurements, cortisol levels in the blood, melatonin levels in the saliva, levels of other hormones, blood pressure, gene transcription, immune cell activity, subjective alertness, and countless other parameters. In 2007, I have finally been able to see the same effect in the circadian changes in memory recall and consolidation in SuperMemo. At the root of human 24h periodicity is the activity of the suprachiasmatic nucleus (SCN) in the brain, which is driven by a 24 hour cycle of gene transcription changes running a classic feedback loop. Tiny mutations in the genes responsible for the circadian periodicity may lengthen or shorten the period of the circadian cycle. They can also lead to complete arrhythmicity. Many of such mutations have been studied in fruit flies and in mice. Human mutations leading to sleep phase disorders are also known (e.g. familial ASPS). However, those mutations are rare, and for a vast majority of healthy humans the length of the period is slightly longer than 24 hours. Dr Charles Czeisler has measured it to be 24.2 hours with amazingly little variation among individuals under the conditions and within the sample studied (Czeisler et al. 1999[55]). The circadian cycle (incl. the gene transcription and the activity of the SCN) can be prodded and shifted slightly on a daily basis. The degree of the shift is determined by the phase response curve (PRC) and requires a very precise timing of the phase-shifting stimulus (Khalsa et al. 2003[56]). In other words, with a stimulus such as light, physical activity, or social interaction, we can move the period of maximum sleepiness slightly. Although the precise measurements of the PRC speak of the possible shift of up to 3 hours in a single day with a single strong stimulus, it is hard, in practice, to shift one's circadian rhythm by more than 1 hour per day. We all get a little backward prod daily when we try to fit the 24 hour day. This daily resetting is painless for those who apply the principles of sleep hygiene. It occurs in the morning with light, activity, and/or stress. An increasing portion of the population use the alarm clock to do the job that should naturally be done by sunlight and activity. This is not a healthy solution and is usually forced by our electrically-lit lifestyle with evening TV, evening reading, evening Internet, evening partying, etc. For those out of phase, it is easier to shift the sleep schedule to later hours (e.g. by activity late in the night) than it is to shift it back (e.g. by bright light in the morning). This asymmetry comes from the fact that we can consciously control the waking hours, which can only be used for a forward shift. It is easy to will oneself to stay up late. It is far harder to will oneself to wake up early. Naturally, an alarm clock can be used to accomplish the latter, but use of alarms should be avoided in chronotherapy and in healthy sleep due to disruptive effect of alarms on the progression of sleep cycles. While it is possible to shift the sleep phase, we do not know any biological mechanisms that could be used to significantly reduce the length of a healthy sleep block without inducing a degree of sleep deprivation. Shortest effective sleep can be accomplished on a free running sleep with strong morning resetting stimuli and strong evening phase delay stimuli. However, even natural stimuli can induce a degree of sleep deprivation. Shifting the sleep phase has a relatively small effect on the length of the main sleep block. The change is proportional to the degree of shift and has the same sign (i.e. shift delays reduce the length of subjective night sleep). Most importantly, the change reverts to the baseline shortly after the shift. This illustrates the homeostatic nature of sleep control mechanisms that respond to phase-shifting stimuli by stabilizing the new sleep schedule at the new offset within a very short time as long as shifts are small enough and are generated by well-timed phase shifting stimuli. A more decisive intervention in the sleep patterns may result in circadian chaos. In Siberian hamsters, it can even cause arrhythmicity (Ruby et al. 1996[57]). Those dramatic changes can have a serious health effects and may be difficult and slow to reverse. The well-defined effects of natural stimuli that affect sleep patterns lead to an instant conclusion: the claim that humans can adapt to any sleeping pattern is false. A sudden shift in the schedule, as in shift work, may lead to a catastrophic disruption in sleep control mechanisms. 25% of North American population may work in variants of shift schedule. Many shift workers never adapt their sleep pattern to the shift pattern. At times, they work partly in conditions of harmful disconnect from their body clock, and return to restful sleep once their shift returns to their preferred timing. At worst, the constant shift of the working hours results in a loss of synchrony between various physiological variables and the worker never gets any quality sleep. This propels an individual on a straight path to a volley of health problems, which include cardiac disorders, suppression of the immune system, diabetes, gastrointestinal disorders, obesity, depression, chronic fatigue, sleep disorders, etc. Shift-workers are also at a higher risk of accidents and family problems (e.g. experiencing higher divorce rate). Shift-work design should apply the laws of chronobiology to minimize the adverse effects of shiftwork on health. It is often better to keep workers working by night on a constant basis than to induce a regular sleep disruption and stress on a weekly basis by a cycle of never-ending schedule shifts. It appears that polyphasic sleep encounters the precisely same problems as seen in jet lag or shift-work. Adult human body clock is not adapted to sleeping in patterns other than monophasic or biphasic sleep. In other words, the only known healthy alternatives are:

a single 6-8 hours sleep block in the night, or a night sleep of 5-7 hours combined with a 15-90 min. siesta nap. Those numbers differ substantially across the population and there is no single recommended dose of sleep for everyone.

If a degree of pressure is exerted on the body clock, e.g. by going to sleep later than the body's optimum, the mid-day nap may serve as a compensatory buffer counteracting sleep deprivation. In such conditions, the nap may last longer than the usual 15-30 minutes. The more pressure is applied on the night sleep, the longer the siesta nap. Similar biphasic consolidation can also be produced experimentally in rats. It appears that with sufficient pressure the nap may become longer than the night sleep, effectively reversing the sleep pattern by 12 hours. This effect confirms an important biphasic nature of the human sleep that is not fully accounted for by the present sleep models. In rare cases, individuals may learn to sleep in two blocks of 3-4 hours. However, in a vast majority of cases, the pattern in which sleep occurs in two equal blocks within 24 hours in unstable. In other words, individuals on the proportional biphasic schedule quickly fall back to long-night sleep and short siesta sleep, or back to monophasic sleep. Often, the portion of sleep that occurs during darkness takes the role of the night sleep. However, it is more likely that this role is taken by that portion of sleep that was longer before the establishment of the proportional biphasic pattern. This again indicates the underlying physiological asymmetry between two sleep blocks in a biphasic pattern. In other words, the body remembers which sleep block is the subjective night block, even if that block happens to occur during the daylight period. Through sleep deprivation, by employing the homeostatic component of sleepiness, polyphasic sleepers can increase the number of naps during the day. However, the pattern of one night sleep and multiple daily naps is highly unstable, and can be maintained only with a never-ending degree of sleep deprivation. Naturally, if you happen to use an alarm clock, you can easily run multiple "naps" during your circadian low-time during the subjective night. This is not possible during the subjective day (except in conditions of extreme sleep deprivation). To a degree, an alarm clock can also be replaced with your internal alarm (e.g. thinking "I must get up in 20 minutes"). None of "naps" executed in similar conditions will do the job of natural sleep. They are not only largely a waste of time, but they also contribute to dismantling your sleep control mechanisms. Dr Stampi's research on polyphasic sleep has also clearly identified the forbidden zones for sleep where naps are very difficult to initiate without substantial sleep deprivation. Those zones map well on the biphasic rhythm with the subjective evening naps preceding the core night sleep particularly ineffective for rested individuals. All the above findings inevitably lead to a conclusion that it is not possible to maintain a polyphasic sleep schedule and retain high alertness and/or creativity! As it will be shown later, practice is no less lenient in judging the impracticability of polyphasic sleep for creative individuals. Anecdotal evidence seems to indicate that highly creative individuals perform best in a biphasic sleep pattern. However, the only valid rule of a thumb for maximizing creativity and alertness is to sleep then and only then when you feel sleepy. When this rule is applied, individuals may fall into a number of diverse schedules. They might be quite effective in any of these exemplary mono- and biphasic patterns: typical 7+2 or 6+1, long sleeper's 9+0, short sleeper's 4+1, or even 4+0, etc. Only you can determine which schedule is optimum in your case. However, you can expect that if you are a normal healthy individual, this schedule will not be polyphasic (other than biphasic). If you attempt 3+0.5+0.5+0.5, you will either be seriously sleep deprived (i.e. you will maintain the schedule only with the help of an alarm clock), or you will revert to 3+0.5, or more likely, you will fall back onto a standard 6+1 pattern. The possibility of hooking up your naps to the ultradian rhythm without sleep deprivation is a myth.

5 years since the Uberman Big Bang In the years 2002-2005, I noticed an exponential increase in the interest in the Uberman Sleep Schedule. I kept receiving more and more mail with questions about the impact of Uberman on health and learning. As a result, I wrote Polyphasic Sleep: Facts and Myths. In the course of the five years that followed, I received some 500 pieces of mail and got in personal touch with many polyphasic sleep adepts. Of those attempts that I was given a chance to monitor, all were unsuccessful. Some of the critics of the original article claimed that they do sleep polyphasically, but I received no data that could serve as the basis for verification. The most interesting conclusion coming from the mass of mail received is that people drift towards polyphasic sleep less as a result of their hunger for achievement, and more for their prior problems with sleep. They often think of polyphasic sleep as a panacea for all their sleep problems. This perception is magnified by multiple blog claims. I received a couple of SleepChart data submissions demonstrating how difficult the struggle with the polyphasic sleep is. Admittedly, I was quite impressed with the degree of determination some of those experimenters showed. As the newest version of SleepChart makes it possible to model the changes in sleep propensity, it provides some insights into the phase-shifting chaos that occurs in polyphasic sleep. With every passing day, we know more about polyphasic sleep and its potential impact on health. The news is not good for the proponents of the polyphasic sleep as a lifestyle. The mail that I have received in reference to my polyphasic sleep article was mostly critical, but it should not be used as a measure of success. It is not important what proportion of readers would agree with me. It is important how many gave up the idea of sleeping polyphasically as a result. Within the five hundred pieces of mail, I roughly estimate the distribution of their nature as follows: 50% - criticism, 40% - requests for help in implementing polyphasic sleep, and 10% - word of gratitude for the warning against adopting polyphasic sleep. 10% may seem like a very low conversion rate. However, this translates to hundreds of hours of someone's time. I am sure it also translates to tangible health benefit. For example, a great deal of polyphasic attempts end up with a cold or influenza, which must reflect the impact of this sleep schedule on the immune system. What Aaron wrote is pretty representative of the 10% group: "The idea of sleeping in naps spread throughout the day intrigued me as I have always suffered from what I was unable to properly quantify, but now know is DSPS. If I do not use an alarm clock, and go to sleep when I become tired, I see my sleep/wake times shift to significantly later times every day (hours later). This has been a constant source of frustration for me, and I considered a polyphasic schedule in order to help correct the problem. However, after reading "Polyphasic Sleep: Facts and Myths", I have decided this would be a sincere waste of my time". Criticism of my article would usually skirt around the science argument and quote from blogs of people who claim they have succeeded with polyphasic sleep. For example Kop wrote: "There are MANY people who successfully adapted. [...] You simply neglected to cite them, and you cited only people who failed. I think this is very unfair and misleading to your readers. I may sound like a broken record, but even if you believe that everyone who claims to have been successful is lying you should let your readers make this choice and you should definitely not just completely leave out all the information you personally don't agree with".

Compression of sleep stages in sleep deprivation One of the myths of "Uberman sleep schedule" is that it makes it possible to enter REM sleep and skip non-REM sleep stages entirely. That myth is derived from another false claim that implies a non-essential role of deep sleep. I will ignore these claims as standing in total disagreement with laboratory findings. Instead, let us focus on a more plausible claim of the possibility of compressing sleep stages in polyphasic sleep. It is true that people who are sleep deprived are able to enter deep sleep much faster than normal sleepers. After a period of sleep deprivation, less important stages of sleep are compressed, while the core SWS predominates. Also REM deprivation will result in REM upregulation at recovery time. Initially, the sleep system will work on catching up with the outstanding SWS, and only later with the outstanding REM sleep (often only on a second recovery night). It appears then that indeed, we are more effective at sleeping after we had been sleep deprived. Moreover, it is possible that the homeostatic control of sleep is not very efficient at detecting the true neural sleep needs. If you look at our mammal relatives, you may be surprised that a giraffe can do well on 2 hours of sleep, while a bat may need 20. Smart and fast-learning elephants need 4 times less sleep than less brainy felines. Behavioral observations will then quickly lead us to the conclusion that the amount of sleep is not directly correlated with the amount and complexity of memory acquisition and neural computation. We may then hypothesize that the sleep control may employ auxiliary physiological parameters that are only loosely related to the requirements of neural optimization. It is also possible, that evolution took account of the fact that the nighttime is not a very useful time for activity in early hominids. Sleep control mechanisms might then have attracted a number of additional physiological functions that might improve survival even if sleep lasted longer than what is needed for memory consolidation and optimization. Hence the possibility of all sleep mechanisms proceeding at leisurely rate with lots of added function that would not require loss of conscious awareness in the first place. If the above thinking is correct, we might indeed be able to execute the same neural job in a shorter time given the favorable circumstances. However, little is known of the true nature of the link between neural optimization and homeostatic sleep control. Our present knowledge still seems to firmly indicate that we can maximize our creativity to sleep cost ratio only with free running sleep. In other words, there is no evidence that by playing with sleep deprivation, you can increase your creativity. The only possible exception might be a tiny degree of deprivation resulting from delaying sleep by 30-60 minutes. Longer delays affect alertness beyond what might be considered a "gain". It is simply possible that between the extremes of free running sleep and a slightly delayed sleep phase, the trade-off between (1) time gain due to sleep compression and (2) an accelerated homeostatic sleepiness might produce an optimum somewhere in between. Naturally, this tiny prod to a sleep cycle has nothing to do with the employment of alarm clocks, shattered schedule and never-ending battle with grogginess typical to those who experiment with Uberman sleep. Moreover, even that little hypothetical intervention in the sleep cycle will inevitably result in phase shifts that may have numerous negative side effects, including, most obviously, the inability to function effectively in a society that is largely synchronized with daylight. Well-entrained and balanced free running sleep is still your best bet for maximum cognitive performance. In sleep deprivation induced by polyphasic schedules, REM sleep will occur faster due to sleep stage compression. Yet it is the slow-wave sleep that is the primary target of homeostatic upregulation strongly determined by the duration of prior waking. As REM sleep is far more associated with the circadian phase, its proportion in sleep will actually drop, esp. in naps initiated in the subjective evening period. You may want to study sleep models by Alexander A. Borbely and Peter Achermann which nicely explain the mechanics of these processes. Laboratory findings seem to indicate that the drop in REM gradually recovers towards the baseline over successive days of sleep deprivation, but the reversal is never complete. In other words, you will get less REM sleep on a polyphasic schedule as compared with a free running schedule. This REM sleep diet is as much absolute (as measured in minutes) as it is relative (when compared with deep sleep NREM). The problem of REM deprivation becomes more pronounced if you use an alarm clock when waking up from naps. By using the alarm clock, you statistically hit REM sleep more often as its proportion nearly always increases over sleep time. This is why polyphasic sleepers often remember their dreams on awakening. That's not a sign you get more REM. It's a sign you are destroying REM sleep. By using very short blocks of sleep, you affect REM even further by a strong homeostatic upregulation of Stage 4 NREM that displaces whatever REM you can get.

Getting more REM in polyphasic sleep is a myth. You will get less REM and your creative powers will dip.

If you (1) do not fight sleepiness and (2) wake up from your naps naturally, the problem of sleep disruption does not occur. However, it is impossible to regularly fit a pre-planned polyphasic schedule without some help from an alarm clock. This comes from the fact that the only stable sleep patterns in healthy individuals are mono- or biphasic. Polyphasic sleep patterns may be stable and sustainable in various cases of hypersomnia, narcolepsy, and other sleep disorders. When the sleep control system is disrupted and the homeostatic sleep component works in overdrive, frequent napping may occur and be recommended (e.g. in infection, chemotherapy, etc.). Needless to say, the total sleep increases in such circumstances. This is exactly what polyphasic adepts are trying to avoid. A degree of sleep fragmentation may also occur as a result of stress, social life, excitement, going to sleep too early, etc. Those disturbances may occasionally allow for days with more than one nap occurring naturally. If you give up the alarm clock, you take away the major culprit that makes polyphasic sleep unhealthy. However, without an alarm clock, it is your body that will decide the sleep schedule, not your pre-planned "rationalized" schedule graph. That schedule will not resemble anything Uberman. If your goal is to get many naps with lots of REM, you might want to know that more than two naps with solid REM sleep are diagnostic for narcolepsy.

Sleep and creativity: Less is more Polyphasic sleep is bad for your health and bad for your creative capacity. However, even if you want to maximize time spent in the waking state it might not be your best option assuming you need a reasonable degree of alertness for whatever you do in your waking time! Only when approaching substantial sleep deprivation can polyphasic schedule be superior to biphasic schedule in that respect (see: PureDoxyk Law). Some people like firefighters or emergency surgeons may sacrifice their sleep for the sake of others. The number of people that need to make a sacrifice can be reduced by a well-designed shiftwork. Most of the remaining population should optimize their sleep for best health and best creative performance during the waking time. Polyphasic sleep is definitely not the answer to such optimization goals. These are not the times of the pyramid of Giza when the genius of a designer had to pair up with 50,000 drudges reduced to mere back-breaking labor. As we move towards the knowledge economy, it is the alert and creative minds that provide the basis of success in most projects. One minute of insight may be worth a century of shoveling! It might have been a single creative eureka that produced E=mc2. Probably even Einstein himself would not be able to track back the exact moment when his brain produced that formula. Nor would he be able to formulate a sure prescription for others for similar accomplishments. Human creativity is primarily a game of chance. Yet it breeds only on fertile grounds. Top-notch mind in a top-notch shape in conjunction with top-notch sleep is the best formula for more of such insights in the future. Polyphasic sleep is the antithesis of that formula! If you scan the blogs of polyphasic experimenters you will see them choose an "engaging activity" again and again just to stay awake. Why would they prefer to meet people or go for a jogging over, for example, getting down to a mentally challenging project? Tony Wright in his attempt at Guinness Record of sleep deprivation (11 days without sleep) realized that he could do anything but writing. After 10 days without sleep, his brain was not up to the challenge of writing even a couple of words. He concluded: As it turns out writing while sleep deprived is easily the most difficult thing to do, for that reason I have decided I won't write anymore, so this will be my last entry. Why would learning a difficult subject be such a mental drag in sleep deprived state? As sports or social interact