- 1 Foreword +
- 2 Importance of sleep +
- 2.1 Why understanding sleep is important?
- 2.2 Why do we sleep? +
- 2.3 Bad sleep kills and costs billions
- 2.4 If you do not sleep, you die! +
- 2.5 Two components of sleep +
- 3 Formula for good sleep +
- 3.1 Free running sleep
- 3.2 Should we free run our sleep? +
- 3.3 Free running sleep algorithm +
- 3.4 Optimizing the timing of brainwork +
- 3.5 Sleeping against your natural rhythm
- 3.6 Kill the alarm clock! +
- 3.7 Sleep inertia +
- 3.8 Health effects of shift-work and jetlag +
- 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 +
- 4.5 24-hour sleep cycle +
- 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 +
- 4.8.5 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 +
- 4.9.5 Synchronous DSPS
- 4.9.6 28 hour day schedule +
- 4.9.7 Curing DSPS and insomnia +
- 4.10 Advanced Sleep Phase Syndrome (ASPS) +
- 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 +
- 4.15 Hypersomnia
- 4.16 Sleep apnea
- 5 Napping +
- 5.1 Napping is good +
- 5.2 Napping myths +
- 5.3 Best nap timing +
- 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 +
- 5.5.12 Charting polyphasic sleep +
- 5.5.13 Claudio Stampi +
- 5.5.14 Sleep deprivation is like alcohol intoxication
- 5.5.15 Sleep debt and napping +
- 5.5.16 Polyphasic geniuses +
- 5.5.17 Sustainability of polyphasic sleep +
- 5.5.18 Caffeine in polyphasic sleep
- 5.5.19 Polyphasic sleep mutants
- 5.5.20 Polyphasic sleep blogs +
- 6 Factors that affect sleep +
- 6.1 Stress +
- 6.2 Alcohol
- 6.3 Caffeine
- 6.4 Sleeping pills
- 6.5 Melatonin
- 6.6 Nicotine
- 6.7 Exercise +
- 6.8 TV
- 6.9 Cannabis
- 6.10 Sex
- 6.11 Diet +
- 6.12 Learning +
- 7 Sleep and learning +
- 7.1 Sleep length +
- 7.1.1 Optimum length of sleep +
- 7.1.2 People who sleep less live longer?
- 7.1.3 Jim Horne and Daniel Kripke +
- 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? +
- 7.3 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 +
- 7.3.7 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? +
- 7.5 Sleep and school +
- 7.6 Learning in alpha state
- 7.7 Learning during sleep +
- 7.1 Sleep length +
- 8 Physiology of sleep +
- 8.1 Why do we fall asleep? +
- 8.1.1 Initiation of sleep +
- 8.1.2 Circadian cycle
- 8.1.3 Borbély model +
- 8.1.4 Phase response curve (PRC) +
- 8.1.5 Recursive phase response curve (rPRC) +
- 8.1.6 Two-component model of sleep in SleepChart
- 8.1.7 REM rebound hypothesis +
- 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 +
- 8.2.6 REM Homeostasis
- 8.2.7 Transition to REM
- 8.2.8 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 +
- 8.3.3 Sleep and memory +
- 220.127.116.11 NREM and memory +
- 18.104.22.168 REM and memory +
- 8.3.4 Synaptic changes in sleep
- 8.3.5 Neural optimization in sleep +
- 22.214.171.124 Hippocampal lesions
- 126.96.36.199 Temporally graded retrograde amnesia
- 188.8.131.52 Memory processing in sleep
- 184.108.40.206 Catastrophic forgetting
- 220.127.116.11 Two-stage memory processing in sleep
- 18.104.22.168 Optimizing memories
- 22.214.171.124 Garbage collection
- 126.96.36.199 Unihemispheric sleep
- 188.8.131.52 Problem solving in sleep
- 184.108.40.206 Conclusions
- 8.3.6 Not all scientists agree
- 8.3.7 Robert Vertes and Jerome Siegel +
- 220.127.116.11 1. Sleep does not serve a role in declarative memory?
- 18.104.22.168 2. REM sleep deprivation does not lead to cognitive impairment?
- 22.214.171.124 3. Sleep-dependent enhancement of procedural learning has not been proven?
- 126.96.36.199 4. Learning in waking is far more significant than overnight enhancements?
- 188.8.131.52 5. Sleep models should be simple
- 184.108.40.206 How can random impulsations in REM make a sense in dreams?
- 220.127.116.11 Dr Siegel's theory of sleep
- 18.104.22.168 My personal bias
- 22.214.171.124 Olive branch
- 126.96.36.199 More reading for skeptics
- 8.4 Clock genes
- 8.1 Why do we fall asleep? +
- 9 Myths and facts +
- 10 Incremental writing
- 11 Acknowledgements
- 12 Glossary
- 13 Summary +
- 14 Sources
- 15 References
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
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. 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)(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)! 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!
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
- 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.)
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)(important: do not confuse this two-stage model with the two-component model of memory (Wozniak et al 1995) or with the two-component model of sleep regulation (Borbely 1982) 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.
For more see:
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