Frequently asked questions about sleep in learning

Most of the questions below refer to the articles: Good sleep for good learning and SleepChart: Formula for healthy sleep

For questions about polyphasic sleep, see a separate FAQ: The myths of polyphasic sleep. See also the body of this file for more answers

Why do we sleep?
(Jose Miguel Molina, Sunday, September 23, 2001 10:49 PM)
Question:
Why do people fall asleep?
Answer:

If you ask about the purpose of sleep: we fall asleep for the brain to get a chance to restructure memories stored during the day and associate these with previously learned things. 

If you ask about the mechanism of falling asleep: it is not entirely understood. Some parts of your brain work by regularly stimulating and inhibiting each other. This produces a daily cycle of activity. Some structures are responsible for inhibiting those responsible for arousal. You get drowsy and the brain goes into a different mode of action: optimizing memory storage. After the work is done, your arousal center gets stimulated again and “get up and go” hormones enter the bloodstream. You are ready for a new day. For more details see Physiology of sleep section in Good sleep for good learning

Question:
I sleep seven hours per day and wake up with an alarm clock. I read that using the alarm clock may negatively affect learning. Is it true?
Answer:
There is a significant body of evidence that the you will get the best results in learning if you get a full night of natural sleep. Many individuals need eight or more hours of sleep. It is difficult to predict how damaging the alarm clock can be in your case. It will mostly depend on how much sleep your body actually needs

Question:
Why does this site not mention learning in the relaxed state? What is your opinion about alpha waves in learning? Do you recommend products like BrainWave Generator, Hemi-Sync, Holosync or Polish Sita biofeedback?
Answer:
We do realize that the proper cognitive environment is paramount for learning. However, for clarity we use the term concentration instead of an all-inclusive relaxation. It is highly recommended that you maximize your concentration by taking into account the following factors:

• being cut off from all sources of interference in learning (telephone, e-mail, conversation, radio and even your favorite music)
• finding the optimum circadian timing for learning (e.g. early in the morning in free running sleep cycle, late in the evening in DSPS individuals who cannot afford free running sleep, etc.)
• all aspects of mental and cognitive health (e.g. stress avoidance, substance abuse, etc.)

The concept of relaxation is often associated with alpha wave learning which has attracted lots of companies that are more interested in their bottom line than their customers actual success in learning. EEG measurements can be used to predicate on the current state of the brain as much as you can predicate on the bustling social life of a major city by scanning the surrounding electromagnetic field. The usefulness of alpha wave scanning in learning can be compared to the usefulness of electromagnetic field scanning in trying to understand human activities in a city. You need to focus on the causes rather than the symptoms. Alpha waves appear primarily in the absence of visual processing and other intense mental processes. This is why they cannot dogmatically be considered as a desired learning state. After all, the drowsy alpha state that precedes falling asleep is exactly the worst moment for learning during your day.

In evaluating the “relaxation products” you need to differentiate between the relaxation effect and the actual learning effect. The number of companies producing false claims in this field is astounding. It is very easy to fall for a simple solution to a learning problem (e.g. get 10Hz binaural beat difference and your learning problem will go away for life, and perhaps your sex drive will improve at the same time, you will sleep better and you will look younger). The “easy learning” bait explains why false claims related to “learning in relaxation” are so hard to extinguish.

At the same time, if you need to cope with stress or insomnia, many products in the field may have a legitimate application. Customers of the Polish Sita system jokingly claim that the company would do better if they marketed their product as a napping system. A worthy application on its own. If you know of relaxation products with legitimate claims and proven results, please let us know. We will gladly write about the subject or provide links from this site

Question:
It is well known that people can be divided into late sleepers, owls, and early sleepers, larks. Has there been any research to indicate what sleeping type has better memory?  
Answer:
The conviction that people are set to be either larks or owls is wrong. Most owls would claim it is virtually impossible to shift to earlier hours of sleep while larks just cannot keep their eyes open late in the evening. However, the reason for this differentiation is largely dependent on the lifestyle. The stereotype is reinforced by the fact that it is indeed very difficult to shift the sleeping rhythm even by a few hours. If you try to force an owl to start getting up at 5 am, you will expose him or her to immense mental and physical torture that may quickly result in serious health consequences! However, with the right approach, an owl can gradually be shifted into an early riser mode! The shift must be gradual as no magic force can instantly override the body’s internal clock. The main reason why owls are owls is that they tend to excitedly spend their time over a book, movie, or computer game till early hours of the morning. They enjoy the quiet of the night when they can pursue their passion. Subconsciously, they try to get as much of the night time for their pursuits as possible. Were it not for school obligations, family or a job, owls might easily shift to going to sleep at sunrise or later. This is why an owl will find it easy to go to sleep later and later, while it will be nearly impossible to gradually shift the sleeping rhythm in the opposite direction (e.g. 20-30 minutes earlier each day). Owls may have a longer clock period or be less sensitive to resetting signals, but they can adopt a farmer’s lifestyle and become larks. If an owl goes to sleep 1 hour later each day, soon it will cycle to sleep through the day and finally start getting up as early as 1-2 am. An owl can comfortably stick to such a cycle for quite long until its natural tendency to go to sleep later each day will not ruin it. Moreover, people isolated from external stimuli tend to fall into cycles slightly longer than 24 hours which also explain why it is easier to prolong the day rather than to shorten the night.
Lifestyle and personality are critical here. Owls may show lots of excitement for learning as this excitement is the main factor that makes them owls. On the other hand, larks can make better use of early morning hours where they can study in quiet at the time when their brains are most refreshed. The formula for best learning is then (1) to go to sleep in accordance with one’s own body clock (i.e. when actually sleepy), (2) to get up naturally (i.e. without an alarm clock) and (3) learn at the peak of one’s alertness (which in a natural rhythm should come shortly after awakening).

Question:
Is it true that it is better to get shorter sleep in the night and then take a few naps during the day?
Answer:
This approach is not likely to benefit your health or learning. Most of all, you should not artificially shorten the night sleep! As for the naps, there is only one major trough in alertness during the day in siesta time (at least in healthy adults). Taking more than one nap is not likely to be needed. Experts on insomnia argue against naps as these may keep people up at night. If your nap lasts only 5-30 minutes and does not affect your ability to fall asleep in the night, it will probably help you be more alert in evening hours. See: Good sleep, good learning, good life

Question:
Isn’t Good sleep for good learning article overly dramatic? Most of my friends cut their sleep with alarms during the week and they aren’t dumb people!
Answer:
The cigarette metaphor is very useful in understanding the problem of sleep deprivation. A cigarette smoker will often tell you: I feel great when I smoke! I cannot imagine life without cigarettes. I do not think it is unhealthy. If it is, why does it make you feel so good? Only epidemiological research demonstrates the multi-billion dollar impact of smoking on the economy. Similarly, seriously sleep deprived people feel miserable enough to succumb to their body clock demands. When they get a chance to catch up, many report feeling better than if they had not been sleep deprived in the first place. It is nearly impossible to notice a damage to memory consolidation. Only scientific research reveals the truth, and the true societal cost of sleep deprivation and shift-work still remains to be fully quantified

Free running sleep implies little stress
(M. Zmuda, Poland, Fri, 8 Feb 2002 10:17:03 +0100)
Question:
If any change is stressful, can free running sleep be stressful too?
Answer:
Saying that any change is stressful is a generalization going 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. Watching news on TV can provide a creative adrenaline-based incentive. Watching September 11 news might have left people in overstress for weeks. 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 to its internal needs. As such, these can be considered anti-stress factors. It refers to sleep, eating habits, exercise, and other physiological needs

Question:
The Good sleep for good learning article says that I cannot remember if I do not sleep. However, when I do not get enough sleep, I have problems with concentration, most of all. What is worse then, not sleeping before or not sleeping after learning with SuperMemo?
Answer:
Despite what is written in Good sleep for good learning about memory consolidation in sleep, not sleeping before learning would probably be more expensive in terms of lost work. If you do not sleep after learning, you will not consolidate memories and this will most likely affect retention of new short-interval material. However, if you do not sleep before learning, you will dramatically decrease your retention in a given session. This will naturally not be a result of forgetting. It will simply result from problems with focusing on the material and getting poor scores on otherwise well-remembered material. Consequently, many long-interval items will reenter the learning process with short intervals. This always significantly increases your workload

Question:
I read that too much sleep may result in a “worn-out syndrome”. Good sleep for good learning article seems to contradict it! What is the explanation?
Answer:
The “worn-out syndrome” can be observed when a heavily sleep-deprived individual sleeps unusually long (above 13 hours). It is very difficult to persist in long-sleep routine as the sleep-regulating mechanism will quickly regulate the length of sleep to a more typical length. On one hand, the “worn-out” syndrome might seem to persist if the sleep period is wrongly adjusted to the circadian cycle (see the section on hypersomnia above);  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 next week’s obligations. This deepens the wrong conviction that too much sleep is harmful. Healthy individuals cannot take “too much sleep”! Their brain will simply produce natural waking up at the right time

Question:
Sometimes I sleep over 9 hours and still feel tired. Usually 8.5 hours is enough for me. What could be causing it?
Answer:
Most probably you are sleeping against your circadian cycle. This could occur most likely after a major shake-up in your sleeping rhythm (e.g. after a few all-nighters, or a few days of waking up very early with alarm clock, etc.). Try to stick to regular sleeping hours and understand your circadian cycle. Many long-sleepers occasionally do not get enough despite sleeping quite long. Trivial factors such as stress or weather can easily put you out of synch

Question:
I live in a small apartment with my parents and two brothers. I cannot use your advice on free running sleep. It would be impossible to coordinate with the rest of family
Answer:
You can still try to free run. If your sensitivity to zeitgebers (esp. light) is good, you do not necessarily have to run in non-24 hours cycles

Question:
If I did not use alarm clock for my after-dinner naps, I could wake up at 10 pm! This is not realistic!
Answer:
If your nap launches you into a 4-5 hours sleep, you are dealing with a case of severe sleep deprivation! You should start off with getting enough sleep in the night. In other words, you need to give up the alarm clock in the morning as well. If you use the alarm in the morning, you enter into a vicious cycle of sleep deprivation and perpetual dependence on the alarm clock

Question:
What for should I measure the time between night sleep and the nap? Can’t I just nap when I’m tired?  
Answer:
Napping is a skill. Many people cannot nap even if they are sleepy. Measuring the time should help you optimize the timing. Optimally, your tiredness will not be visible enough to easily guess the optimum timing. If you measure the time between night sleep and the nap, you will notice that the length is always the same (variations depend on the quality of sleep in the night). In other words, this helps you figure out the timing of your circadian dip even on days when you do not feel tired

You cannot remedy sleep deprivation by anything but quality sleep
(luisgustavo, Brazil, Thursday, January 03, 2002 4:42 PM)
Question:
Perhaps short periods of sleep deprivation are bad because they are a source of stress. But how bad it can be depends on how can you handle stress
Answer:
It is true that the turmoil in the cortisol-epinephrine system will make you more susceptible to stress in sleep deprivation, but it is not true that stress management can be a solution to sleep deprivation. It is true that a good diet might improve the health of a smoker, but diet alone does not solve the problem of smoking. The only ultimate solution to smoking is no smoking. Similarly, the only ultimate solution to sleep deprivation is sleep

Question:
I like the idea of free running sleep. It seems to work nice. I work from home and getting up late is not a problem. However, how do I synchronize with my wife?  
Answer:
If you both try free running sleep, your 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 you have similar interests and daily routines). Probably one of you will just get up slightly earlier and work as a strong zeitgeber for the other. The problem will appear only when the length of your cycles differ substantially. In such cases, instead of being a zeitgeber, the other person becomes a substitute for an alarm clock

Question:
I have read hundreds of articles on the web and they all say that naps should be avoided! Good sleep for good learning article seems to say the opposite 
Answer:
You are probably referring to articles related to insomnia. Indeed, people who have problems with falling asleep in the evening, report that avoiding naps makes the problem less severe. However, this is nothing else than promoting night sleep by increasing daytime sleepiness. In free running conditions, naps usually come early, are short and do not affect the ability to fall asleep quickly in the evening. On the other hand, they certifiably increase the intellectual performance in the second half of the day (cf. Aschoff, Dinges)

Question:
I heard a fatigue expert say that she recommends coffee just before the nap. Good sleep for good learning article contradicts this. How do you explain that?
Answer:
Probably the expert referred to a quick restorative nap, e.g. in case of a drowsy driver. Good sleep for good learning article tries to find the optimum for your intellectual performance. If you drink coffee before the nap, you are likely to awaken earlier as a result of caffeine kicking in. This may be a desired effect if your are in a hurry to combat fatigue. However, an optimum nap in a free running cycle will naturally last no more than 30 minutes, and its effect may be short-lived if it is artificially cut short with a cup of coffee

Question:
I read on the net that there are systems that can put me in theta brainwave. 30 minutes of theta is supposed to replace four hours of sleep. Is this true?
Answer:
No. This is a false claim that has no scientific basis whatsoever. Similar claims should disqualify the site your are visiting as a reliable source of information. As a counterbalance, we would rather recommend: Skeptic’s Dictionary for the New Millennium with valuable information on how to critically evaluate web content. Interestingly: Theta waves correlate with learning which increases the demand for sleep

Question:
If I wake up early in the morning, say at 4 am, what is the recommended course of action? Shall I try to fall asleep or get up and work?
Answer:
Probably you should make your decision on the basis of how fast you believe you would be able to fall asleep. If you do not think the sleep is coming soon, it is definitely better to get up and work. This way you will gain in three ways:

1. get tired and sleepy faster (work is more likely to make you drowsy)
2. you will not get anxious about getting asleep as soon as possible
3. you will not waste your precious time on futile tossing and turning

The best method for falling asleep fast is to go to sleep at the right time
(Zarish Hamid, Jul 23, 2001)
Question:
How can I fall asleep faster without having to think so much about what is happening in my life?
Answer:
There are two weapons against racing thoughts before sleep: 

1. stress-management, i.e. learning to avoid or manage stressful situations 
2. sleep-management, i.e. improving the quality of sleep 

As for sleep management, there is only one sure method: to fall asleep quickly, you have to go to bed at the right time. Racing thoughts are an indication that you went to bed too early, i.e. not being in the right moment of your sleep cycle. If you are extremely tired due to sleep deprivation, it may still not be enough to fall asleep. A huge number of people go to sleep very tired but cannot fall asleep due to stress or due to worrying about how little sleep they will get. The best solution to this problem is free running sleep, i.e. going to sleep only when you feel you will fall asleep immediately. However, this method, for majority of younger people, will result in getting up later and later. In other words, it is incompatible with a normal lifestyle. In such cases, the problem is unsolvable. You need to put up with a degree of stress before sleep, some insomnia and some sleep deprivation. Various methods exist to alleviate the problem (e.g. timing exercise, bright lights therapy, etc.) but they do not resolve the core problem. Only a change in lifestyle could provide a satisfactory answer

The function of sleep is not muscle regeneration
Question:
According to what I’ve read in body-building literature, sleep is necessary for muscle growth and repair
Answer:
If you do not get enough sleep, your body building effort will be ruined. That is true. However, the only known evolutionarily justified function of sleep is the optimization of the memory storage. In other words, your muscles need your sleep, but you do not sleep because of your muscle needs. For the organism to cope with muscle regeneration, there is no need to shut off the central nervous system, and make you unconscious for a third of your life. If REM paralysis was to play this role, it could be enforced at the level of the medulla oblongata without making you unconscious. If growth hormone secretion was to play a role, it can also be upregulated in abstraction from the state of the central nervous system. You may list many other benefits of sleep for muscular regeneration but none will require the state of sleep itself. Using sleep for muscle regeneration would be as sensible as shutting down the government in order to fix a highway. The belief in the role of sleep in regeneration comes from the feeling of being “broken down” and “unrefreshed” once you do not get enough sleep. However, you do not feel crushed because of the damage inflicted by the lack of sleep. Your state is simply your body’s own defense against not getting enough sleep. You can cheat those defenses to a limited extent with caffeine or by waiting for the suitable part of the circadian cycle. No real harm is done. One night of good sleep, and your body is back to shape. The only true damage inflicted by sleep deprivation is to the fabric of your memory. Unfortunately, this damage is imperceptible, and the universal perception is that sleep is cheap and can easily be dispensed with

Sleep is needed for optimizing the memory storage
Question:
Last I heard, it was an enormous mystery to sleep researchers what the purpose of sleep is, though there were a number of theories. If you search Encarta Online, you will read “Although no one knows for sure why we sleep, there are a number of theories“
Answer:
Your perception is not unusual. As with all inventions and theories, they go through some teething trouble and then wait long for a social invention. Some inventions are accepted and developed quickly (e.g. Guttenberg’s print, Tesla’s AC current, etc.), others linger for years in oblivion (e.g. Babbage’s “computer” or Tesla’s or Nelson’s “WWW”). Some theories are obviously correct and are accepted quickly (e.g. Newton’s laws of gravity), others linger for decades due to (1) lack of “convincing” evidence (e.g. Wegener’s continental drift), (2) religious considerations (Copernicus’s heliocentric system, Darwin’s theory of evolution), or plain bad luck (Mendel’s laws of genetics). Luckily, the evidence for the role of sleep in learning is so convincing, that no serious scientific conference on the physiology of sleep will include more than a few mavericks with their own alternatives. Naturally, every community has its Peter Deusberg who can put the spanner in the works. Hence the editors of Britannica or Encarta must exercise extreme caution in adopting recent scientific findings. A statement “there are many theories of sleep” is safe and obviously true. However, the research community is more than a decade ahead of this statement, and the focus is not on if, but on how. Incidentally, the Encarta articles on sleep were contributed by Prof. Jerome M. Siegel, perhaps the best known opponent of the position that sleep is involved in learning

Free running sleep is best
(Mariusz, Poland, Sunday, July 29, 2001 8:34 AM)
Question:
What will bring more benefits: free running sleep or ultra-dian rhythm of 4 hours? Why?
Answer:
By definition, free running sleep is best. After all, it is dictated by your body’s internal clock. 4-h ultradian rhythm has been invented by sailors who had to stay awake for long stretches of time. Ultradian rhythm is unnatural and can be quite unhealthy. For ultradian sleep to be harmless, you would need to first entrain it and then maintain it with free running sleep. If you try it in real life, you will get a very definite answer to your question

Mid-day crisis is best resolved with a nap
(anonymous, Mon, Aug 13, 2001 22:38)
Question:
Each day there is a moment when I am unable to focus on some task, get tired, and less effective. Drinking coffee does not help. What should I do?
Answer:
First thing to try is a mid-day nap. If the crisis point arrives in between 5th and 9th hour of your waking day, retiring to a peaceful location for a nap (without an alarm clock) is highly likely to solve the problem. Try to time your main meal before the nap. If napping does not help, you should carefully analyze your sleeping schedule and read: Good sleep for good learning. You probably do not need to seek professional help unless your problem cannot be resolved with free running sleep or if you cannot afford napping or free running sleep

Dreams of blind people help us understand the physiological role of sleep
(Terry, Aug 31, 2001)
Question:
Do blind people dream?
Answer:
Yes. Their dreams are more auditory and tactile in nature which confirms the role of REM in replaying daily experiences and optimizing memories. They do not show the typical eye movement pattern in REM sleep either

Reducing sleep without alarm clock
(Mohammed, Pakistan, Sunday, April 14, 2002 2:34 PM)
Question:
Is it possible to reduce sleeping hours without using alarm clock?
Answer:
Yes. If you free run your sleep, the quality of your sleep will increase, and your average sleeping time is likely to decrease (as compared with sleeping it out in irregular rhythm patterns). You can also reduce your sleep time by intending on waking up early. However, thinking of getting up earlier is stressful and may negatively affect the quality of sleep.

Afternoon downtime
(M.A. Khan, Sunday, April 14, 2002 2:34 PM)
Question:
My peak time for learning is from 7:00 pm to midnight. I don’t feel sleepy and my mind runs like a tiger. My problem is that when I come back home from the university at 3:00 pm, I am always less effective. Then I try to get some sleep
Answer:
Your being less alert at 3 pm is quite natural. Most of us experience a trough in alertness around that time. Your peak evening performance might indicate a minor DSPS problem, which is also quite typical for studying adolescents. If you get up without an alarm clock in the morning, you have nothing to worry about. You can use your low after-school time for some more relaxing activity. No need to feel guilty about it!

6.5 hours of sleep per night might be just right
(T.J.Jensen, Feb 23, 2002)
Question:
You disagree with the recent study on the optimum length of sleep. I understand your point. However, Dr Kripke says that those who sleep 6.5 hours per night should not worry. I sleep just about that. Why do you say I have reasons for concern?
Answer:
Probably you have misread our message on optimum sleep. No one should worry about sleeping 6.5 hours or even 4 hours, as long as he or she sleeps naturally, wakes up naturally and feels refreshed. The key point then is in how you get your 6.5 hour. If you wake up without an alarm clock and feel alert throughout the day, you have all reasons to call yourself a good or even excellent sleeper (few people can live without an alarm clock). On the other hand, if you wake up with an alarm clock and feel tired, you are certainly doing yourself a harm. There are naturally many stages in the middle which cannot be answered through a simple FAQ. It is not how much we sleep but how we sleep. Our message is mostly targeted against the use of alarm clocks and sleeping pills in regulating sleep

Waking up short of breath may indicate sleep apnea
(Jose Miguel Molina, Sunday, September 23, 2001 10:49 PM)
Question:
My Mom is 50 and looks healthy. However, every night when she goes to sleep she would wake up short of breath as if always coming from a nightmare. She would say she feels like she’s falling to a deep valley
Answer:
The symptoms described are typical for sleep apnea. This means that your mother may have a problem with breathing during sleep. This wakes her up and ruins her sleep. Exercise, sleeping on the side, and weight loss may help in mild cases, but do not fail to insist your mother see a sleep expert. Sleep apnea may result in an increase in blood pressure and a heart condition. A patient may look healthy and normal, but in the long run his health may suffer substantially

Occam’s razor for SleepChart
(Leon J., Oct 04, 2004, 08:28:40)
Question:
I think that what you are proposing with regard to how we manage our sleep is just far too complicated and that Occam’s razor needs to do a bit of shaving here – I mean, come on! Sleep’s as natural as breathing air or drinking water and if you have to set up complicated charts and experiments, and utterly eccentric sleep-activity patterns just so as to get some decent shut-eye, then you must have a problem – but one more of a psychological than a physiological nature
Answer:
Sleep will occur naturally in a natural setting. The trouble begins when we interfere with nature using caffeine, alcohol, nicotine, artificial lighting, 24/7 society, night-time entertainment, etc. SleepChart may seem complex, but it might still be the easiest way to predict the optimum timing of sleep in free-running conditions (probably there are no equivalent tools available as of Oct 2004). SleepChart will only ask you when you go to sleep and when you wake up (naturally). All computational complexity is hidden in the background. The approximation procedure needs no further input from the user and it predicts circadian lows as well as the optimum timing of going to sleep. For those who are interested, SleepChart can even disentangle homeostatic and circadian components of sleep. As we are dealing with the physiology of sleep, by definition, we are indeed within the realm of psychology. The problem can be solved with behavioral tools too. One of the most effective tools is the application of free running sleep

Music and sleep
(Mohammed Asad Khan, Thursday, May 02, 2002 1:01 AM)
Question:
I want to be awake for 3 days with the help of my favorite music? Is it possible?
Answer:
Unless you do a research on ravages of sleep deprivation, you should never force your body to go against your natural sleep-wake cycle! The longest natural waking period rarely goes beyond 20 hours. Beyond that you must go to sleep. Otherwise you will negatively affect your health and learning. You can use music as an invigorating factor though. The rules applied here will be similar to those for using coffee: never use music, coffee or other stimulants to prevent descending circadian sleepiness. Use mild stimulants only on the ascending circadian after you wake up from the night sleep (or after a properly timed nap). In simple terms you can help your body wake up, but you cannot try to prevent it from going to sleep!

Striving at lucid dreaming is a waste of time
(anonymous, Jan 12, 2006, 00:20:20)
Question:
What is your stand on lucid dreaming? Can this be used to enhance learning, or creativity? How about personal growth, super-consciousness and experiencing hyperreality?
Answer:
Lucid dreaming is as useful for learning and creativity as LSD. Striving at lucid dreaming is rather likely to disrupt your healthy sleep and negatively affect learning. During REM sleep, the prefrontal cortex should normally be de-activated. Hobson’s AIM model of 3D sleep-wake space can be used to illustrate the state corresponding to lucid dreaming as a partitioning, in which the cortex and the rest of the brain occupy different points in the AIM space. Such partitioning is likely to interfere with the physiological function of REM sleep. It can be compared to eating your lunch while jogging (i.e. the situation where contradictory targets are fed to the nervous system). Using auto-suggestive tricks to change the AIM state may affect neural processes occurring in sleep with unpredictable consequences that are not likely to be positive. As for creativity, it is conceivable that LSD (and less so lucid dreaming efforts) might boost non-specific creativity or help understand the creative process; however, most of the mankind’s creative breakthroughs occur when a healthily refreshed mind focuses on solving a specific problem. Hallucinatory haze is not helpful in directing creativity towards useful purposes. Creativity is a game of chance. You should look for ways of consciously directing the creative process rather than to increase its randomness indiscriminately. As for super-consciousness and hyper-reality, you are addressing the question to a wrong party. At supermemo.com, we firmly intended to remain within the realm of science.

You cannot “more or less” free run you sleep
(Bart, Netherlands, Sunday, October 07, 2001 10:35 PM)
Question:
I have been struggling with getting a good quality sleep for years (my symptoms resemble DSPS). I more or less followed a ‘free running sleep’ during my student years: every night I went to bed later and every morning I woke up later until I would go to bed at around 5 am. But I just could not continue this shifting scheme. So I always tried to go back, with getting up early and slowly changing my rhythm
Answer:
Your actions are understandable and typical for DSPS. However, you cannot “more or less” free-run your sleep. Once you try to “go back” to the old rhythm, you violate free-running sleep principles and you cannot call it free running sleep any more. Your experiences will not translate directly to the free running condition. In other words, to draw your conclusions on free running sleep, you have to truly give up the alarm clock and all other forms of regulating sleep (e.g. going to sleep later than natural, etc.). If this is not possible in standard circumstances, you could try during the nearest vacation. If you collect data on your sleep cycle, please forward for analysis and further comments

All forms of sleep “regulation” should be avoided
(ZM, Thu, Nov 29, 2001 12:00)
Question:
Even without an alarm clock, I noticed that late falling asleep gives me a bad night. I usually get up at 6-8 no matter when I fall asleep. After one New Year’s Eve, I fell asleep at 7, and got up at 8
Answer:
Yes. This is exactly what you should expect in a healthy individual. Your arising hour is strongly dependent on your circadian cycle and it is only slightly shifted by going to sleep late. As much as an alarm clock, delaying sleep is also a form of sleep regulation and should be avoided. The only exception is when delay is executed in order to fit the circadian cycle. Delaying retirement may be less drastic than using the alarm clock (the sleep cycle is not interrupted artificially), but is also highly detrimental to sleep quality. As for your New Year’s Eve, you would better wait until the next sleep cycle and go to sleep, for example, only at 15-19, so that your strong homeostatic sleepiness would let you sleep until your evening circadian low kicks in giving you many hours of sound sleep. Better yet, you could cut your party short at an earlier hour

The good sleep may not apply to you
(B.D., Poland, Tuesday, February 26, 2002 1:46 PM)
Question:
What can I do living with my wife and son in one bedroom apartment? I can only try to get rid of the alarm clock, but still most of my wake-up calls come from my son being hungry
Answer:
Admittedly, most of the principles of good sleep are impossible to meet for many. In richer countries shift work, stress, or family life are to blame. Elsewhere poverty or little understanding of health matters are only a few of factors that make good sleep so elusive. For young parents, a child is a factor that adds an insurmountable challenge. Probably all you can do is to maximize love in the household, try to take rational duty shifts with your wife, and get as much sleep as you can whenever there is an opportunity. With time it will become easier and easier to synchronize the family life and give everyone a chance to begin the day all smiles

Sleeping in wrong hours may be as bad as not sleeping at all
Question:
If deviations in habitual sleep time produce performance losses equivalent to those produced by shortened sleep (Taub & Berger, 1976), does it not imply that sleep deprivation is not as important as the disruption to the circadian cycle itself? Perhaps sleep is not as important as keeping the circadian rhythm?
Answer:
No. It is true that sleep in wrong hours may be worse than no sleep at all but this only indicates that sleep needs to be properly synchronized with the circadian cycle to play its physiological function. A delicate neurohormonal balance triggers individual phases of sleep that interplay in optimizing memory storage. The quoted research should only strengthen the conviction that the societal damage produced by alarm clocks is enormous

Free running sleep is a blessing
(luisgustavo, Brazil, Thursday, January 03, 2002 4:42 PM)
Question:
Sleep is important, but there is no conclusive study showing temporary sleep deprivation is terrible
Answer:
You are right that there is no evidence of “terrible” damage produced by sleep deprivation (except for horrifying truck accident statistics, airtime disasters, etc.). However, if you ask anyone who tried free running sleep for more than a month about the cost of sleep deprivation, you are likely to hear a very definite private research conclusion: “Never back to the days wasted by lost or irregular sleep“. The contrast between good sleep life and bad sleep life is so dramatic that you will find no one who hesitates about the difference once it is exposed in practice. As adrenaline and cortisol are good masks for sleep deprivation, the above is particularly true in creative professions with mild to severe adrenaline deficit

Free running sleep does not imply abnormal sleeping habits
(M.Zmuda, Poland, Fri, 8 Feb 2002 10:17:03 +0100)
Question:
Is there a big difference between a normal sleeper and a free running sleeper, if the normal one:

• is woken up by sunshine 
• doesn’t use any drugs
• sleeps enough for his/her body (could be 6 or 9 hours) 
• takes naps (if feels the need) 
• uses the same sleeping hours
• avoids stress 
• feels rested after sleep 
• and lets body use zeitgebers

Answer:
What you have just described as a “normal sleeper” is by all standards a lucky free running sleeper. The main criterion of free-running sleep that has not been listed above is if the “normal sleeper” uses an alarm clock. If you do not use an alarm clock or other sleep control tricks, you are a free running sleeper. As you indicate that your “normal” sleeper “sleeps enough”, he or she is not likely to use an alarm clock that would cut the natural sleep. As he or she “feels rested”, the sleep is most likely healthy and physiologically sound. As he or she “listens to zeitgebers”, the sleep again seems to be regulated by natural factors. Your “normal sleeper” can be considered lucky because in addition to using natural sleep, he or she is able to sleep in regular hours, is rested and wakes up with sunshine. As many people suffer from a degree of DSPS or ASPS, your “normal” scenario may be difficult to reach for many. The DSPS/ASPS problem is particularly painful in the student community, in overstressed working population as well as in many elderly

The problem of waking up in the night
(Chris I., Hungary, Nov 03, 2002)
Question:
Why do I often wake up in the night?
Answer:
If you wake up during the night, you should identify and eliminate possible reasons, esp. if you appear to wake up tired. The reasons and the way to diagnose them are too many to describe in a short answer. However, you should always start from the simplest one: problem with the circadian rhythm. In simple words, the timing of your sleep may be wrong. Partitioning of sleep is a typical symptom of going to sleep too late or going to sleep too early. If you are healthy, in free running sleep, you will rarely wake up during the night; and if you do, the reasons will be quite obvious such as: stress, noise, thirst, coldness, full bladder, etc. However, if you attempt to regulate the timing of your sleep, the partitioning of sleep (i.e. interrupted sleep) will be a frequent result. It is possible to push your sleep slightly ahead or back (e.g. 15-25 minutes per day) without this negative outcome. However, once you try to push too hard (e.g. more than an hour per day), partitioning is almost inevitable. If you push backwards (i.e. going to sleep earlier and earlier), you will likely wake up early in the night, i.e. before your circadian low ensures deep sleep. On the other hand, if you push forward (i.e. going to sleep later and later), your circadian low will end before you complete your sleep cycle. As a result, you will often wake up earlier than expected. If this waking up happens very early (when you push ahead very hard), you will be tired enough to fall asleep again. In other words, whichever way you push your sleep, it will not be properly aligned with your circadian rhythm. You will then wake up early or late in the sleep cycle depending on at which end the misalignment occurs. In a vast majority of cases, waking up problem can be resolved by going to sleep at the time when your body calls for it. However, if free running sleep does not remedy the problem, you may need to consult a sleep disorders expert

Sleep period and genetics
(Robin C., United Kingdom, Fri, May 31, 2002 0:44)
Question:
I am sure that the free running sleep period is not entirely determined by genetics
Answer:
You are right. 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

Sleep length depends on the circadian phase
(Dr J.N., Jun 14, 2002)
Question:
Does the sleep onset hour affect the length of sleep?
Answer:
It may but it does not have to. The most powerful factor affecting the length of sleep is the circadian phase. In a normal patient, the circadian rhythm is aligned to the 24 hour period. Thus the sleep onset hour will be directly related to the length of sleep. Maximum length of sleep will occur with the sleep onset falling roughly between 22 and 3 am (depending on the individual rhythm). However, in a free running DSPS patient, this relationship is lost. In DSPS rhythm, the graph of the function of the sleep length vs. the sleep onset hour is horizontal, i.e. the length of sleep does not change (on condition the rhythm is running free without a disturbance). Here are a simple rules to determine the expected sleep length: 

• The maximum quality of sleep is achieved when the sleep begins during a strongly ascending circadian sleepiness
• The shortest sleep is achieved when it is initiated towards the end of the circadian sleep propensity 
• The longest (but not necessarily most refreshing) sleep is achieved when it is initiated well before the ascending sleep propensity 

Never go to sleep when you are not sleepy. Never force yourself to work through high sleepiness. If feasible, always go to sleep when you feel your body wants to go to sleep

Which component of sleep is best correlated with the fresh feeling in the morning
(Terry, Jun 15, 2002)
Question:
Which phase of sleep is most important for the fresh feeling in the morning?
Answer:
Stage 4 NREM sleep (“deep sleep”) correlates strongly with feeling fresh. However, a proper structure of sleep is also vital. To get lots of Stage 4 NREM:  adhere to your circadian rhythm, exercise, and avoid NREM-suppressing medication. Although you get lots of NREM early in sleep, cutting down your sleep with alarm clock will likely take away all freshness as soon as the homeostatic sleepiness kicks in. For that reason, you should sleep as much as your body wants to

Owls, larks and procrastination
(Monica White, Oct 04, 2002)
Question:
Is it true that owls are greater procrastinators than larks: http://dubinserver.colorado.edu/prj/jph/index.html
Answer:
The presented mini-survey is flawed. Depending on the elected population sample, the correlation might yield highly varied results. There might be a link between a circadian type and procrastination. Obviously, people who sleep poorly are more likely to procrastinate. This comes directly from an impaired prefrontal control in sleep deprived people. However, it would seem likely that all forms of departure from the standard 24 hours entrainment would affect executive control. This way, “normal people” should be best at executing their own resolutions. Departure towards both DSPS or ASPS might negatively impair self-discipline. As distribution of DSPS and ASPS in different age groups varies, running a survey among students is likely to link owls with procrastination. However, the same survey among retirees might yield an opposite result. ASPS is by far more frequent in older people due to inherent changes in the circadian cycle that occur with aging. Naturally, free running sleep is likely to dissolve the link between morningness and procrastination. In conclusion, good night sleep is certainly a good remedy against procrastination

It is possible to fall asleep immediately
(valeko, Apr 15th, 2002 at 09:18:23 PM EST)
Question:
It seems that a good sleeping rhythm relies on the ability go to asleep immediately, which I do not have, even in the most tired physiological state. It takes me around one hour to fall asleep, almost regardless of how tired I am
Answer:
You need to remember that your “sleep tiredness” has two components: homeostatic and circadian. You believe that you are awfully tired, but if this is only a homeostatic tiredness, you can toss and turn for many hours. Homeostatic tiredness grows quickly in conditions of sleep deprivation, while circadian tiredness comes only at a specific time in reference to your body clock. If you are tired of wakefulness but your body clock is not ready, you will not fall asleep. Free running sleep resolves this problem in majority of cases. It might not work if there is an underlying health problem (e.g. excess catecholamines, thyroxin, cortisol, overstress, etc.)

Multiple awakenings in the night
(Diane, Sunday, June 09, 2002 2:49 AM)
Question:
I have a recurring sleep pattern, which I do not understand. There are times, sometimes for a few weeks at a time, where I will go to bed at a normal hour (9-11pm). I go to sleep when I’m tired. However, after sleeping 4-5 hours, I wake up briefly every hour. I am awake for just a minute, then go back to sleep. I typically will get up around 6:30am. So, a typical night in this scenario might look like this: 

• 11pm – go to bed 
• 3am – wake up, may include trip to bathroom 
• 4am, 5am, 6am wake up for a minute, go back to sleep 
• 6:30am wake up w/o alarm clock, generally refreshed

Answer:
There does not seem to be anything troubling in the above rhythm. The best part is that you wake up without an alarm clock and feel refreshed. The brain has a top-quality system to let you know when you did not get enough sleep; you just feel miserable. Multiple awakenings during the night are not unusual. However, most of us are not aware these short breaks ever happen. If there is a trip to the bathroom in the meantime, reducing fluid intake 2-3 hours before sleep might help (naturally). You seem to get a good 4-5 hours of deep sleep and then wake up briefly after periods of REM-rich sleep. Nothing in that rhythm indicates departure from the healthy brain physiology. The periodicity of the above symptoms could be related to seasonal or temporary changes in hormone levels. On the face of it, you got nothing to worry about. Nevertheless, it is always a good idea to seek second opinion in health matters

How to improve evening alertness
(jona, Netherlands, May 11, 2004, 20:11:00)
Question:
Do you have any suggestions on how to acquire optimum alertness at a, for me, unusual, evening time of the day?
Answer:
You will always obtain best alertness if you adapt the timing of activities to your natural rhythm, and not if you try to adjust your body clock to the outside world. 

A simple alertness booster, such as caffeine is only likely to last for a short while, it is not likely to eliminate the reduced capacity for learning, and worst of all, it could interfere with your sleep cycle making things worse in the long run. 

An afternoon nap could do wonders if properly timed and executed along the principles of the art of napping. A creative evening is a norm among skilled nappers. 

However, nothing would work as well as moving the activities that require high alertness, learning or creativity to the time where the alertness is maximized naturally (which for most healthy people is not long after awakening from the night sleep)

Variable sleep length is an indicator of non-free-running sleep-wake cycle
(Dr J.N., Jun 14, 2002)
Question:
If the length of sleep is constant in free running sleep, why do sleep logs of DSPS patients show a clear relationship between the sleep onset hour and the sleep length?
Answer:
Such a relationship will only show if the rhythm isn’t a perfectly free running rhythm. Rarely are patients able to disconnect their sleep needs with their need to perform their daily duties in the society. As a result, DSPS patients who claim to free run will often learn tricks to “manipulate” their sleeping rhythm (e.g. trying to accelerate the phase shift before an important appointment, etc.). In an undisturbed free running rhythm, the length of sleep should remain constant.

25-hour sleep cycle
(MTS, Thursday, December 07, 2000 4:20 PM)
Question:
Why is there the 25 hour sleep cycle built-in in us when the Earth’s cycle is only 24 hours?
Answer:
Internal clock runs at above 24 hours due to the fact that we can easily synchronize the day with our body clock by the use of zeitgebers (mostly sunlight). This way the oscillator with a slightly longer period is set to synchrony with the daylight by a minor SCN-mediated reset. This provides for a very stable oscillation. This mechanism goes awry by the use of artificial lighting as well as due to providing us with exciting evening activities such as watching TV, surfing the net, playing computer games, reading, etc. People suffering from DSPS could experiment with light dimmers, toning down their schedule in the evening, properly timed exercise and bright light in the morning. People with ASPS should use opposite measures (e.g. 3000 lux light in the evening)

The three things you need for good sleep
(Ravi, Monday, March 28, 2005 6:30 PM)
Question:
My name is Kevin. I am in grade 8. I am doing a science fair project. What do you think are 3 things necessary for a good night of sleep?
Answer:
There are many things we need for sleep. Some of these are obvious, e.g. a comfortable bed. Those things are hard to compare. It is as much as wondering what we need more for life: the brain or the heart. We simply need both. Let’s rephrase the question to make it useful for an average poor sleeper. What are the main 3 things people do wrong when trying to get good sleep?

These might be top 3 bets for good sleep:

1. Do not use the alarm clock: everyone whose sleep is substantially cut short with an alarm clock knows that it can ruin your day. Yet 50% of people in industrialized nations wake up with this murderous device (add to this 9% woken by a partner, 4% awoken by pets, 3% awoken by children, etc.). With a shot of strong coffee and round-the-clock stress, most people learn to live and survive with an alarm clock. Few understand the damage they incur on their brains as a result. At the very minimum, interrupted sleep will reduce the power of the brain to make order in memories (memory housekeeping is the purpose of sleep). At worst, sleep deprivation and stress 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)
2. Go to sleep when you are sleepy: amazingly, most people do not care to listen to their body. Many struggle with sleepiness to get more life in the evening. Others force themselves to bed long before their optimum bedtime and then toss and turn for hours. This premature landing in bed is at the root of the epidemic of insomnia (even though the official figures put circadian disorders at only 10% amongst the causes of insomnia). The only sensible and healthy time to go to sleep is when you feel you start getting sleepy
3. Avoid substances regulating sleep: most frequently, people abuse caffeine to fight sleepiness. Unless this is a mild tea or coffee on awakening, caffeine can send mixed signals to your brain, heart and other organs (e.g. the brain tells your heart to slow down, coffee tells it to speed up, etc.). Contradictory research on the impact of coffee on health comes from the fact that some people drink coffee at the “right time”, while others try to compensate sleep deprivation. In addition to caffeine, alcohol before sleep is the second worse offence. A drink before a nap is ok. The same drink before the night sleep may disrupt sleep structure. Thirdly, sleeping pills should be avoided whenever possible (unless prescribed by your physician). Even using melatonin to affect the sleep phase may negatively impact free running circadian rhythms. We know thousands of substances that affect sleep, yet we do not seem to know any that can effectively help us regulate the circadian rhythm without side effects. This is why we struggle so much with alarm clocks, insomnia and sleep deprivation.

One might hesitate about the third point: perhaps avoiding stress is more important than avoiding sleep-affecting substances. However, most people cannot run away from stress in their job or in family life. It is far easier to skip the evening drink or a cup of coffee than to resolve a gnawing conflict at work. Hence the third choice.

You may now be wondering what you should do if your body tells you to go to sleep at 3 am, while your school begins at 8 am. Nobody has yet provided a satisfactory answer to this question. Ideally, the school should adapt to your rhythm. Some schools tried this. But then … your rhythm may shift further and later school hours stop being helpful. Returning to the Stone Age, or to the times before electricity is not an option. We can only hope that the science of sleep will come up with a cheap, healthy and lasting solution

Alarm clocks that detect your sleep phase do exist
(L’el, Nov 02, 2005)
Question:
I read somewhere that there’s an alarm clock that’s being developed that’s keyed to the users sleep cycle
Answer:
Yes. This alarm “clock” has been developed millions of years ago. It makes up part of our brain and is responsible for the release of “wake up” hormones (such as cortisol) at the time when we should optimally get up (i.e. once we are through with all vital sleep phases). This alarm clock is smart and adjustable. If it is not interfered with much, it perfectly aligns our sleep cycle with the cycle of day and night. And the best part is … it comes free with installation at birth to every healthy individual

You cannot learn much from tapes while you are asleep
(Esquire Magazine, Wednesday, March 23, 2005 9:22 PM)
Question:
Can I really learn by listening to tapes while I sleep?
Answer:
No. Your brain uses sleep to do memory housekeeping. This is a very important process without which learning is not possible. Using a computer metaphor, you can imagine that during waking hours, you load information into your memory, while during sleep you do disk defragmentation. Naturally, your computer can survive without defragmentation. Your brain will not survive without sleep. All learning processes grind to a halt in conditions of sleep deprivation (i.e. insufficient sleep). While you are asleep, the brain is busy with memory housekeeping, and it cuts itself off from the external world. For the most part, this means that it will perfectly ignore the tape playing in the background. However, if the tape is noisy or annoying, it may disrupt your sleep. As a result, you might be actually learning worse when using the tapes. It may happen that you recall pieces of the tape playing throughout the night. This is because of the way the brain works in sleep. It goes through a series of well-planned cycles. At the end of each cycle, your mind will be very close to the waking state. It may pick up pieces of information. However, those states may result in various forms of hallucination. In other words, you can mix things up and rearrange information into a new meaning. You can learn things upside down! All in all, stay away from quacks offering you learning in sleep! The best thing you can do for your learning in the night is to sleep as much as your body wants. Try the so-called free-running sleep. Free-running sleep is sleep dictated solely by your brain. If you can afford it, throw away your alarm clock. Your alertness, your joy of life and your learning powers will be at the maximum

Non-24h free-running sleep might be a lesser evil
(Leon J., Oct 04, 2004, 08:28:40)
Question:
I found your sleep article too extreme. If you work solidly 8 hours a day, have 3 decent meals, have a proper family life, and treat other people as human beings, then in the evening you go to bed happily knocked out and wake up next morning happily refreshed. Surely this is as it always has been for most people throughout history and surely this is how it will always remain
Answer:
Unfortunately, your perception is not unusual. Those who are lucky to experience good sleep will always find it difficult to understand those who have problems in the sleep department. This attitude is not much different, however, from telling a clinically depressed person: “Pull yourself together“, or expect a heroin addict to go cold turkey and instantly return to normal life. A tortured insomniac will only get more upset with himself or herself if (s)he is told that sleepless nights come from “unsolid work”, “indecent meals”, “improper family life” or treating others “inhumanely”. The trouble stems from the clash of biology with modern lifestyle. With the arrival of artificial lighting sleep disorder statistics skyrocketed. These were only made worse by television, computer games and the Internet. With the advent of mobile telephony and instant messaging, insomnia and sleep phase disorders seem to reach epidemic proportions. Fewer people are able to leave work behind, cope with stress, or give up evening activities. Without a major change in lifestyle or a breakthrough in circadian control methods, people affected with lifestyle-related sleep disorders are faced with a choice between a daily sleep deprivation misery and radical solutions such as throwing away the alarm clock. Certainly, we can expect science to come up with answers to the problem. Until that happens though, waking up “happily refreshed” remains a privilege of a shrinking subset of the population in industrialized nations

If you love to wake up at 3 pm, doing so might be your healthiest option
(Abe B., Thursday, April 27, 2006 12:43 AM)
Question:
I find that I seem to sleep best (i.e. sleeping just the right amount and awaking feeling refreshed) from 6-7 am till 2-3 pm. I can consistently go to sleep those time frames. Going to sleep any earlier or later is a struggle for me. When I’ve made a point of going to sleep at midnight or any earlier than 6 or 7am then I still sleep until 2 or 3pm. Sometimes this has resulted in my getting 12-14 hours of sleep–which is an annoying waste of time, and also seems like poor quality of sleep. In other words, when I go to sleep at midnight, I really can’t wake up until 2 pm or so–even if I set multiple alarm clocks. What’s worse is that the sleep doesn’t feel refreshing. I feel groggy. Your research seems to indicate that I should be able to set my sleeping times to whatever I want them to be; be it going to sleep at 9 pm and awakening at 5 am … or any desirable setup
Answer:
It is possible to use chronotherapy to shift your sleeping rhythm, but it is always a struggle if it goes against your natural inclinations. In other words, there are ways for you to start falling asleep at midnight and waking up early, but your description indicates that it is unlikely to be a stable sleep pattern. Your 14 hour sleep is easily explained with the fact that your circadian low time falls somewhere between 9 am and 2 pm. If you succeed in falling asleep at midnight, your sleep between midnight and 6 am is of little biological value. As a result, you may indeed feel groggy and waste extra hours on unproductive sleep. A very strong rule of good sleep says that it makes little sense to try to sleep when you are not sleepy! Your sleep rhythm is a combination of lifestyle, your particular sleep control system, your interactions with the environment, etc. Your biology seem to interact with your environment in such a way that waking up at 15:00 becomes a natural and stable routine. If it does not ruin your life professionally, sticking to this rhythm might be chronobiologically simplest, cheapest and, paradoxically, healthiest solution. However, you should investigate what factors contribute to your staying up late, and perhaps shift the balance to slightly earlier hours, e.g. by avoiding late night TV, lighting, work with a computer, etc. You could also add some intense exercise and exposure to strong light in the morning. The fact that it is possible to shift your rhythm is not a recommendation to do so. You have to weigh up pros and cons. It is probably healthier to synchronize your sleep with night-time, but forcing such an unnatural synchrony may cause more damage than good. Your best options are: keep studying chronobiology, keep studying your own sleeping preferences (e.g. use SleepChart to plot your patterns), and try tiny experiments with what factors help you shift your rhythm to more “standard” hours.

Can learning be arousing? 
(Mariusz, Nov 09, 2007, 07:53:09)
Question:
I found the following on Dr Dement’s website in his guides to better sleep: “Avoid heavy studying or computer games before bed, they can be arousing“. Do you question one of the greatest authorities on sleep?
Answer:
With due respect, the quoted sentence is quite imprecise. There is no doubt that computer games are arousing and should be avoided. However, “heavy studying” can take many forms. If you study for an exam, and this brings stressful images of the exam itself, you can indeed be aroused. If you study a fascinating subject that monopolizes your thoughts, it can be arousing as well. Similarly, learning in a brightly lit room may slow down the descent to sleep. However, if you extract the pure learning process devoid of stressful associations, light, social aspects, etc., you will come to a different prescription. Learning is definitely associated with the homeostatic component of sleepiness, and can promote sleep. 

Here are the suggestions: 

1. select some unexciting learning material (e.g. your French vocabulary could pass the test, unless you plan an exciting trip to Paris)
2. subtract the high priority material (learning in a drowsy state can negatively affect the learning process in that subset)
3. make sure that your monitor and your room are not too bright. Otherwise you may impact your sleep phase that will make sleep harder on the next day

NASA study contradicts your claims in “Good sleep” article
(Georgios Zonnios, Oct 11, 2006, 08:50:28)
Question:
Here is a webpage outlining a NASA experiment on naps. They say that while naps can improve ‘working memory’, they do not generally improve general vigilance and alertness. This is obviously contradictory to “Good sleep, good learning, good life” article which says: “The drop in alertness [during midday] is magnified by a rich meal and a short nap is likely to quickly bring you back to full alertness“
Answer:
Various measures of alertness, vigilance, and/or working memory should all correlate closely with your ability to learn or with your ability to recall information from memory. Data produced with SuperMemo seem to indicate without any doubt that your ability to learn increases dramatically after a nap, even if the nap lasts just a few minutes. 

In healthy subjects, some ambiguity may arise when naps are taken at a wrong time. A good nap falls roughly in the middle of a waking day. A nap that comes too close to the night sleep is likely to produce an “inertia effect” and may actually decrease alertness. Instead of being a nap, it comes closer in effect to an interrupted night sleep. 

In simple words, if you are healthy, if you are skilled in the art of napping, if you take naps at the right time and, if you just feel better after a nap, you can be sure that your memory, learning ability, alertness, and other cognitive parameters will all be up. Naps are definitely good for learning. Except for people with certain sleep disorders (incl. severe insomnia), naps are good for health. We should all work to eliminate the stigma of laziness often associated with napping, and promote napping, incl. napping at workplace (if feasible and safe).

Sleep control mechanisms are imperfect
(Russ Turk, Apr 19, 2007, 02:28:17)
Question:
In the modern day with electricity and other stimulants at night, free sleep will most likely result in a cycle greater than 24 hours. But for our ancestors, who “could expect little but darkness and boredom past sunset”, sunset and sunrise adjusted their circadian rhythm so that it was a 24-hour cycle and fit with the 24-hour day. Since days are longer in the summer than in the winter (sunrise is earlier and sunset later) does this mean that our ancestors slept more in winter than in summer? Was there a need for more sleep in winter? If they indeed slept more in winter yet there was no biological need for more sleep, then it seems that they must have been getting either more sleep than they needed in winter or less sleep than they needed in summer
Answer:
Your reasoning is correct. Sleep control mechanisms are not ideal for satisfying our sleep needs. Sleep is primarily controlled by two mechanisms: 

• circadian sleep propensity – this component is very old in terms of biological evolution and has for eons been used to synchronize the life of living organisms with sunlight 
• homeostatic sleepiness – this component is probably directly related to neural functions and reflects the need for sleep to consolidate waking experiences 

As the circadian component is influenced by light, variations in levels of illuminance will cause variations in sleep. It is conceivable then that we sleep less efficiently in winter (in terms of neural effects per unit time). Equally well, summer sleep might be less restorative. Eskimos cut off from civilizational influences sleep a few hours more per day in winter. It is then possible that the use of artificial light might contribute to efficiency of sleep (e.g. by delaying sleep onset); however, there is too little data to state that this could be a beneficial strategy. It could as well be deleterious by producing a sleep phase delay, reduced REM, lesser morning alertness, etc. 

Prof. Jim Horne is right that in some circumstances we sleep more than we really need to. However, he goes too far when he compares sleep to eating (one might conclude that alarm clocks are similar to a healthy diet). 

Excess sleep does not bring any tangible biological advantage for control mechanisms to favor long sleep. Conservation of energy is minimal, and the brain may actually use more oxygen during some sleep stages than when working on complex tasks. Even though lions might sleep 20 hours per day when there is shortage of food and water, humans, in normal circumstances, can only binge on sleep after periods of sleep deprivation, when sleeping in a wrong circadian phase, or when they experience health problems. There are many factors that might increase the demand for sleep (e.g. learning, exercise, etc.), or shift the sleep control mechanism to favor sleep over wakefulness (e.g. brain injury, infection, poisoning, hypothermia, etc.).

In conclusion, we need to realize that sleep control mechanisms are not perfect; however, we have not yet come with any artificial and certified ways of improving upon what we were given by the biological evolution. Natural free-running sleep is still the best way to accomplish healthy and refreshing sleep.

Why do synapses get weaker during sleep?
(J., Jan 30, 2008, 18:13:11)
Question:
NYT has reported on a research (http://www.nytimes.com/2008/01/29/science/29obslee.html)  that sleep weakens the synaptic strength. At the same time, synaptic strength increases during waking. This seems to go against your own findings that you published on your website that indicate that during the day one’s ability to recall facts seems to be waning
Answer:
There is no contradiction between the fact that synapses get strengthened during waking and the ability to recall things drops at the same time. First we need to differentiate between (1) short term increase in synaptic conductivity that is a result of learning, and (2) the ability to recall long-term memories (as they are tested during learning with SuperMemo, which was used to produce the data). 
Secondly, we need to look at the most likely explanation for the weakening recall during waking. The most coherent, attractive and best-supported hypothesis says that the overload of short-term low-interference networks is responsible for a declining capacity of memory during a waking day. This decline cripples the working memory, and in consequence, it affects the entire spectrum of human cognitive capabilities. The main function of sleep would then be to redistribute, reconsolidate and optimize those short-term memories that slow down further learning. To put it metaphorically, the brain is like a computer that keeps loading chunks of data to its memory during the day. As the memory fills up, the computer slows down, and all applications crawl into a halt. However, if you test individual memory cells, you will notice that they strongly cling to their new data. In the night, the computer will gradually organize the chunks of data, remove discrepancies and duplicates, write down memories to the hard disk, and run a defragmentation process for easy and fast access. Both the increase in synaptic conductivity in wakefulness, and the decline of learning capacity during the day are well documented. 
As for the decline in synaptic strengths during sleep, it also fits well with the present models of sleep and learning. One of the main functions of sleep should be to optimize the memory storage. This entails representing memories in most efficient way, i.e. so that they are most abstract, consume least space, generate minimum interference, and so on. That process should indeed result in reducing the overall cost of memories, and result in weakening of redundant synaptic connections.

Optimum nap time is best determined with statistics
(Georgios Zonnios, Monday, October 09, 2006 11:10 AM)
Question:
How can there be an optimum nap-time? Your article states the following: Homeostatic sleepiness increases with the length of time we stay awake Naps are a needed solely to get rid of homeostatic sleepiness. Since naps are meant to be kept short, I understand they can’t have a circadian component. Therefore it seems logical that the two-processes model does not explain the optimum timing for naps! After all, as long as you stay awake your homeostatic sleepiness continuously increases
Answer:
Your reasoning is correct. The two-processes model of sleep propensity does not explain why we best nap at mid-day. The two-processes model can be understood as the first iteration of the ultimate model of sleep and wakefulness. Borbely, Achermann and other researchers continue to enhance the model to better explain various phenomena without making the model overly complex. The “optimum nap time” is a concept that is best explained by mathematics. The optimum nap time is the time, somewhere in the middle of your waking day in free running sleep, that produces the maximum probability of falling asleep or the minimum average sleep latency. 

You can easily plot your optimum nap time with SleepChart. SleepChart collects your sleep block statistics and can accurately point to the time of day where your naps might be most beneficial. The only conditions you need to meet are: (1) you need to free run your sleep (SleepChart uses a technique of predicting your homeostatic and circadian sleepiness that only works for natural, undisturbed sleep) and (2) you need a few weeks of your sleep data to make the reading accurate. 

If you are a seasoned napper, you probably already know your optimum nap time, and you can use SleepChart to confirm your observations. If you are new to napping, you can start with naps in the exact middle of your waking day, and adjust the precise hour using SleepChart and your own observations. For example, if you cannot fall asleep, your nap might be too early. If you sleep too long, it might be too late, etc. 

As for the biological explanation, it is worth knowing that there are a number of brain nuclei involved in sleep. Each is responsible for its own input processing. Each produces an output that depends on the input and its current state. Your napping will be affected by factors such as stress, temperature, exercise, weather, exposure to light, and many more. The circadian factors are also multiple. Apart from the levels of circulating hormones, body temperature, etc. there are different phases for REM propensity, SWS propensity, ultradian cycles, and other lesser components of your circadian pattern. Sleep researchers are only gradually finding out the enormous complexity of all these interconnected mechanisms. The sleepiness hump in the middle of the day is produced by homeostatic mechanism on one hand (i.e. you will not fall asleep easily if you take a nap too early), and by circadian factors on the other; for example, the forbidden zone of sleep that marks increased alertness in the evening. The paradoxical increase in the alertness in the evening (without or without napping) comes from the fact that there is a temporary increase in alertness hormones that can combat homeostatic sleepiness. However, this may also mean that despite the fact that you do not feel sleepy, your memory and your creativity won’t be as crisp as in the morning (unless you took your mid-day nap). To make things more complex, late evening napping may also be affected by the possibility of catching onto the circadian low of the early night. This can potentially fragment your sleep and disrupt the healthy sleep pattern. Wrong timing of a nap produces negative effects that make some experts oppose napping as a healthy habit. All in all, even though the biology of napping is complex and not entirely understood, the statistics are quite clear and should help you learn to nap effectively even if you have always thought you were not a natural napper.

Maximizing attention
(Isaev, Vladimir, lis 23, 2005, 15:45:17)
Question:
What do you think is the best way of increasing the span and quality of attention in learning and in creative work?
Answer:
Attention is subject to daily fluctuation along the circadian cycle. It is also subject to homeostatic depression with prolonged mental work. In other words, everyday you got only short windows of time when your attention is maximum. In addition, your total mental energy that can be extracted in each window is limited. Understanding the timing of your circadian rhythms and the natural limits on the attention span might be the first step to take to optimize the timing of mental effort. Once you know the optimum time for creative work, you can maximize attention through neurohormonal control. Again you may need some understanding of psychophysiology and your own mental needs to accomplish this goal. Your primary tool here is passion. If you learn how to become passionate about the task at hand, you are likely to maximize attention. In addition, you can learn to apply lesser tricks such as exercise, caffeine, ambient temperature, intervening tasks, etc. Those need to be used with caution as they can easily backfire. Again, nothing works better than trial and error backed up with some knowledge of the physiology of mental effort. Last but not least, in learning, you can substantially increase attention of less interesting subjects is you use the incremental approach. Incremental reading improves your attention by including attention along your priority criteria. In incremental reading, you can always temporarily de-prioritize the material that undermines your attention. As the effect on attention is highly context dependent, you can always find the best moment at which you tackle a particularly difficult subject

How costly is is to skip nights of sleep? 
(David Moberg, Sweden, Saturday, May 17, 2008 6:59 PM)
Question:
If I sleep well during most time of the year, how would it affect me to skip 1 night of sleep or sleep just 50% of my needed hours 2 nights in a row? How unhealthy is it to do this ~4 times a year in connection to parties, birthdays, christmas, conventions?
Answer:
It is not possible to quantify the effects of such violations. Most of conclusions on the effects of sleep deprivation on health come from restrospective analyses that make it hard to produce clear-cut correlations. The answer falls somewhere within the scope of the statement “it is definitely not healthy”. Judging by the scope of violations people commit on their sleep in general population, skipping sleep 4x per year is not much. Your own body can probably provide you with some measure of the effect. Some of the negative aspects of sleep deprivation are exaggerated and disappear after a single night of good sleep. Others may be imperceptible and more deleterious (e.g. when your violations affect the phase of sleep in a way that tips you out of balance for days to follow extending the damage for perhaps as long as one week). The negative effects will affect nearly all systems in your body as these all change function along the circadian cycle. Your best strategy should be never to skip nights and, if possible, never use the alarm clock. But if you do, the negative effects will add up in the long term and will still be very hard to measure. You just cannot take a copy of yourself to see “what if”.

Insomnia may be both biological and psychological
(insomniac, Oct 31, 2010)
Question:
Do you think insomnia physical or psychological?
Answer:
There are many types of insomnia or many factors that contribute to insomnia. For younger studying population, the most frequent cause of insomnia is related to sleep phase problems. For students who need to get up for school early, their sleep phase is often positioned too late in reference to the desired waking hour. In other words, the optimum sleep time comes too late. Sleepiness arrives too late, and natural waking comes later by the same degree. Such a student will always battle with sleep deprivation when going to sleep late, or a degree of insomnia when going to sleep early. In that sense, there is a physical/biological underlying cause. However, as sleep deprivation is pretty unpleasant, a student may try go to sleep early (to ensure the night is long enough), but be unable to fall asleep due to the early circadian hour. If this occurs again and again, a psychological component may compound the problem. The recurring sleep deprivation will produce a fear of not falling asleep or waking up and making things even worse. In short, in a vast majority of cases the problem is both biological and psychological. The only true remedy is to go to sleep later and wake up later thus being late for school (perhaps a lesser evil). The only natural half-remedy is to measure as precisely as possible the optimum time of going to sleep, and sticking to that time religiously every day. That optimum time is the earliest time that roughly provides 95% or more certainty that sleep latency will be less than 10-15 min. (i.e. no more than a quarter of an hour of tossing and turning). Very often, this optimum time will provide for a mere 3-5 hours of sleep. However, this sleep is most likely to be the best quality sleep achievable in such conditions. Naturally, affected individuals will suffer a degree of sleep deprivation on a daily basis. This is still better than futile tossing and turning, waste of time, and fitful sleep associated with insomnia. If you suffer from sleep-onset insomnia, and you suspect it could be caused by a delayed sleep phase, you could research additional remedies such as morning sports, strong morning lights, and radical solutions such as … giving up electricity after 19:00.

Why do newborns sleep so much?
(anonymous, 2001)
Question:
Do babies sleep so much because they’re learning so much or are they learning so much because they are getting so much sleep?
Answer:
Babies sleep so much because their brains have been designed to do so in the first months of their life. They do learn a lot, and learning does increase the demand for sleep, but this is not the main regulatory factor. Sleep control systems in babies simply work differently, and you probably would not be able to make babies sleep less by making them learn less. On the other hands, long bouts of sleep are used to reorganize neural networks in the brain. You could probably do a serious damage by trying to deprive a baby of sleep. In short, sleep helps learning, learning induces sleep, but the whole sleep sequence is a direct outcome of a genetically programmed properties of a young sleep control system.

Free running sleep may collide with a “normal” lifestyle
(M.B., Netherlands, Nov 11, 2010, 01:06:21)
Question:
I am free running my sleep. I had an appointment at 17:30. I expected to wake up around 15:00 as in the previous three days. Instead I woke up around 17:00 still a bit tired. I had to skip my morning routine (meditation, breakfast, supermemo, etc.). FRS works really well for me. But today sucked. It was really stressing having to run due to waking up later than expected
Answer:
Free-running sleep will often produce a phase shift. If you tend to wake up very late, you will also tend to wake up later each day. This is a hallmark symptom of delayed sleep phase syndrome (DSPS). DSPS, however severe, is never a health problem if you can free run your sleep. However, it will often cause scheduling problems. You will need to swing towards one of the two extremes: either make your life less dependent on meetings and appointments that can collide with your sleep schedule, or study DSPS remedies that can stabilize your sleeping phase. Even if you wake up late, waking up always at the same time, makes scheduling much easier. If you do not opt for one of the above extremes, you will risk collisions that will make your days, as you say, “suck”. What is even more dangerous, if you disrupt your sleep rhythm on a free-running schedule, you can often lose synchrony between various circadian variables. This will result in a situation in which for a day or even a few days, you will not be sure of your optimum sleep time. Even SleepChart may be unable to make a good prediction. This will inevitably result in poor quality sleep, and a few days of lower productivity

Solutions for people suffering from DSPS
(Aaron Burtle, , Oct 01, 2009, 23:36:26)
Question:
I recently came across your write up regarding polyphasic sleep. The idea of sleeping in naps spread throughout the day intrigued me, as I have always suffered from what I was unable to properly quantify, but now know is DSPS. If I do not use an alarm clock, and go to sleep when I become tired, I see my sleep/wake times shift to significantly later times every day (hours later). This has been a constant source of frustration for me, and I considered a polyphasic schedule in order to help correct the problem. However, after reading “polyphasic sleep: facts and myths”, I have decided this would be a sincere waste of my time. I was wondering if you had any experience with helping those who have DSPS maintain a more, “normal” schedule. Is a bi-phasic sleep schedule more suitable for someone with this sleeping disorder (sleeping from 2-7am with a nap from 1-2pm for example)? Google has told me that the most common treatments seem to be rotating ones sleep until they line up with civilized society and then using something like bright light therapy to keep the clock reset. Will this be treating the symptoms alone or actually getting at the root problem? Do you know of any other techniques which could help me situation?
Answer:
Probably, most of the cases of DSPS can be explained by a lack of compatibility between the genetically determined sleep regulatory system, and the lifestyle. You can easily cure the disorder if you decide to change your lifestyle. However, such a change is usually not feasible due to the type of employment or family life conditions. This means that you are probably, for a while, sentenced to a constant battle with your body clock. 

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

Using a biphasic sleep like you describe (2-7 am, 1-2pm) is a good idea. However, you must be aware than naps taken too late are likely to delay the sleep phase making matters worse (even though the same naps can be a blessing for your mental performance, alertness and creativity). 

Needless to say, polyphasic sleep does not bring any advantage to a DSPS person. In DSPS, you suffer because of a slight misalignment of your main circadian low. Polyphasic sleep disregards the circadian cycle entirely making matters worse. Ad hoc napping (as opposed to planned/artificial “Uberman” napping) is a reasonable way to alleviate sleep deprivation, however, (1) it needs to follow your natural brain needs, (2) it may have a detrimental impact on the cycle itself (often worsening the degree of DSPS). 

In conclusion, DSPS epidemic can be considered a civilizational disorder in which the pressure of a modern lifestyle stands in disagreement with millions of years of evolution. In the long run, once we fully understand all biochemical and hormonal processes underlying sleep, it is possible that mild pharmacological intervention will make it possible to regulate the circadian cycle. Currently, this is possible to a degree, but you are bound to experience side effects and research on the matter is still scant.

An expert on TV said clearly that we get lowest alertness at 8 am, and then it progressively increases. This is opposite to what you claim!
(anonymous, , Oct 20, 2009, 10:15:29)
Question:
An expert on TV said clearly that we get lowest alertness at 8 am, and then it progressively increases. This is opposite to what you claim!
Answer:
Lowest alertness at 8 am might be true for people who go to sleep too late and wake up with an alarm clock. However, it is definitely not true in free running sleep. The person who got lowest alertness at 8 am would most likely keep sleeping till 10-11 am and only then wake up naturally. If you use SuperMemo and collect your sleep data, you can see clearly on your alertness graph, that alertness is highest at the beginning of the day (perhaps starting with the first hour after awakening due to the transition from sleep to wake that sometimes may take some time). Low morning alertness can only be explained by the misaligned circadian rhythm. If circadian lows occurred earlier, morning would be brisk and alert. In other words, the expert might be right. Most people wake up too early and are sleepy throughout the morning. But this is a situation we should all strive to eliminate by getting sufficient sleep and sleeping in the optimum hours.

Alertness graphs show nothing
(Steven Zhong, China, Jun 10, 2011, 10:10:01) Question:
In my SuperMemo, Alertness graphs show nothing or show error messages.
Answer:
To see how your alertness changes in the course of the day, you need to first log in your sleep data. Moreover, you need to make repetitions on the days you log your sleep. If you have no sleep data, or sleep blocks are not interspersed with repetition blocks, you will not be able to see your alertness graphs in SuperMemo.

Sleep timing may be more important than the total amount of sleep
(J. P., Jun 21, 2011, 21:30:51)
Question:
Does one’s bedtime have any importance if they are getting the total amount of sleep his/her body needs? For example what is the damage, if any, one is doing if he/she changes bedtimes from 10pm-6am to 3am-11am for work, school, social activity, fear of vikings, etc?
Answer:
Bedtime may be more important than the total amout of sleep. You always need to sleep at the time when your body clock says it is your subjective night. You will get more benefit from 2-3 hours of sleep at the right time (your night), than from 8 hours at the wrong time (e.g. when jetlagged in Japan). Note that it may be hard to get 8 hours during the subjective day without a serious prior sleep deprivation. If you feel more refreshed after sleeping 3am-11am, you should use it instead of the “conventional” 10pm-6am. You can also shift your subjective night bracket with chronotherapy, however, maining those “less natural” hours may require lots of self-discipline and knowlege, if you are a typical “owl”.

Segmented sleep is not your optimum way of sleeping
(Damian Yates, Apr 7, 2013, Sun, 00:15)
Question:
Many websites say that 4 hours of sleep followed by 2 hours of being awake then another 4 hours of sleep us more healthy and say that studies show that people live longer with this method, is this true?
Answer:
No. This is not true (unless this sleep pattern comes naturally). If this was to be your natural pattern, you would have probably discovered it years ago. The sites you mention might be referring to segmented sleep, which is an expression of having “too much time for sleep”, e.g. as in long nights without electricity. This type of sleep might be healthy if you can induce it naturally, e.g. by giving up on electricity and all forms of nighttime work or entertainment. However, this may also be a very inefficient way to spend your nights. In natural free running sleep, your nights might be just 5-6 hours long (esp. if you complement that night sleep with a siesta). Natural sleep is always best and it does not need to consume many hours of your day. You can read more about segmented sleep here: http://www.super-memory.com/articles/sleep.htm#Segmented_sleep

Instead of looking for a perfect sleep pattern in literature, learn about free running sleep, and you will soon know what works best for you. Read about free running sleep here: http://www.super-memory.com/articles/sleep.htm#Formula_for_good_sleep

Sleep is not for closing eyes only
(عبدالله ابو محمد, Tue, 19 Feb 2013 00:30:33 +0300)
Question:
In my research, I have concluded that sleep serves only one function: closing the eyes. Loss of consciousness follows only due to boredom. Note that fish that do not have eyelids do not sleep. There is more evidence to prove my thesis.
Answer:
Science says that sleep serves neural function. The body of evidence is huge. You cannot ignore all that evidence and build your own theory based on a couple of observations. You can easily disprove your thesis by mechanically forcing a human being to keep his eyes open (with some irrigation to prevent corneal damage). Sleep will follow inevitably. That sleep will largely fulfill its function even during daylight (light has a major impact on sleep phase, not on sleep quality). To begin serious theorizing, you would need to answer the immediate question: if the function of sleep is to close the eyes, what is the function of closing the eyes?

What is sleepy potion?
(ﳿ, Wed, 25 Sep 2013 11:27:46 +0800 (CST))
Question:
I’m reading your article, Good sleep, good learning, good life, and I have a question about it: What actually is the sleepy potion in Clock and Hourglass metaphor? Is that melatonin?
Answer:
Melatonin will correlate well with the concept of the “sleepy potion” as it indeed is primarily released during the subjective night. However, “sleep potion” should have a wider and more precise meaning as “all circadian-based processes that generate consolidated night-time period of high sleep propensity”. This will then include melatonin, but will also involve neural processes, e.g. firing in the SCN, etc.

Optimum length of nap in biphasic sleep
(Lucas Zieland, Wed, 24 Jul 2013 11:56:19 +0800)
Question:
I was wondering whether you had an opinion on whether biphasic sleepers should have a 20-30 or 1.5 hour nap? I’ve heard that taking a 20 minute nap can be sustainable with a 6 hour core sleep, thereby saving an average of 1.7 hours in a day, but don’t want to undergo a change to this sleep schedule if it is similarly unnatural or unhealthy
Answer:
The only natural and healthy length of the nap is the length programmed in your brain. This means you should go to sleep at the right time (usually 7-8 hours from natural waking), and wake up naturally. Natural waking may take place in 3 min or in 60 min. In most people, unless they are sleep deprived, siesta rarely lasts longer than 2 hours. You should never think of saving time on sleep because you will likely end up sleeping longer or getting sleep deprived. The shortest healthy sleep you get on well-timed free running sleep.