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).

Contents

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.

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 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, : "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

- 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

: 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[glossary]. 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

- 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:

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.

- 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.

- 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 launches 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, 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

- 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.

). 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 alertnes