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Sleep and dreams

The Sleep/ Dream/ Wake Cycle

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Experience : Does your brain sleep when you do?
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Tool Module: Brain ImagingBrain Imaging

Recent Studies on the Role of Sleep

Non-REM sleep accounts for about 75 to 80% of your total sleep each night, or about six hours of non-REM sleep if you sleep eight hours in total. You spend the remaining two hours–roughly 20% of the night–in REM sleep.

It seems that with training, people can gradually reduce their normal amount of sleep by an hour or two without feeling too tired.

In any case, that is what seems to have happened in developed societies over the past century. In 1910, the average adult slept 9 hours per night, whereas today, the figure is only 7.5 to 8 hours. Two factors that surely go some way to explain this change are electrical lighting, which makes it easy to increase the number of hours of available light, and the increasing emphasis placed on productivity-related values over the intervening century.

The main difference between being awake and being asleep is that in the latter state, consciousness does not intervene. When you’re asleep, it’s somewhat as if your brain were closing itself off and becoming a sort of “temporary autonomous zone”. But in reality, your brain is never completely cut off from the rest of the world: even during the deepest stages of sleep, a strong enough stimulus from your environment will be perceived by your brain and may cause you to wake up.

During REM sleep, your body is completely paralyzed, but during non-REM sleep, it moves frequently, making a major change in position roughly once every 20 minutes.


On every normal day of our lives, each of us engages in two very distinct kinds of behaviours: sleeping and being awake. On the surface, these two behaviours are so different from each other that even extraterrestrials who came to observe life on Earth would notice the difference right away. The entry in their ship’s log might read: “Earthlings spend about two-thirds of each day upright and moving around and the other third lying down and still.”

But what these extraterrestrials would not notice right away, and what even Earth’s own scientists did not begin to discover until the mid-20th century, is that sleep is far from a simple matter of placing our mental and physical activities on hold. Sleep is a genuine “second state", just as varied and complex as the state of wakefulness, and characterized by major changes in physiological characteristics such as body temperature, hormone secretions, heart rate, and respiration rate. Also, far from being uniform, sleep rotates through various stages that occur in a characteristic order in the course of the night.

The stages of sleep that occur after you first fall asleep consist of what is called non-REM sleep, or slow-wave sleep. The slow waves in question are the ones seen on the electroencephalogram (EEG) trace (follow the Tool Module link to the left) of someone who is in these stages of sleep; this trace consists of very slow, high-amplitude oscillations.

These stages of non-REM sleep are followed by a stage of another kind of sleep, in which, paradoxically, the EEG trace looks much more like that observed in people who are awake: the waves are faster, and their amplitude is smaller. Hence this kind of sleep is often known as paradoxical sleep, the name that it was given in 1959 by Michel Jouvet, a French neurobiologist who conducted the first animal experiments concerning it. But this form of sleep is also characterized by numerous rapid eye movements (REMs) that take place underneath the closed eyelids, and hence is usually referred to as REM sleep. Probably the most fascinating characteristic of REM sleep is that it is the stage of sleep in which we experience our most detailed and strangest dreams.

Thus scientists go beyond the observations of our hypothetical extraterrestrials and distinguish not just two but three fundamental behavioural states: wakefulness, non-REM sleep, and REM sleep. Each of these states is generated by a specific pattern of brain activity and accompanied by specific changes in the activity of the body as a whole.

The average adult human sleeps 7 to 8 hours per night. But about 10% of the adult population needs much more sleep at night –9 or even 10 hours–to feel wide awake during the day. At the other end of the spectrum, some 5% of the population can get along fine with only 5 or 6 hours of sleep. Thus there is no particular amount of sleep that is ideal in itself. The only real criterion for whether you’re getting enough sleep is whether you feel in good shape during the day.

The variations in the amount of sleep that people need are determined both by their genetic make-up and by their lifestyle, especially during adolescence. The same goes for people’s tendency to go to bed early and wake up early, or to go to bed late and wake up late. Thus it would be just as silly to say that everyone should sleep 8 hours, from midnight to 8:00 AM, as it would be to say that everyone should wear the same style of shoe, in a size 8.

But regardless of whether people sleep 6 hours or 10 hours per night, they all get about the same amount of deep non-REM sleep: 100 minutes. People who sleep more total hours each night devote some of the extra time to REM sleep, but more of it to light non-REM sleep. Thus people who sleep less might be said to have a higher concentration of deep non-REM sleep than people who sleep more.

In today’s performance-obsessed society, people often cite Napoleon, Louis XIV, and Churchill as examples of high achievers who supposedly slept only a few hours each night. But curiously, people fail to mention all the other high achievers who, like Einstein, needed 10 and sometimes even 12 hours of sleep per night!

Tool Module: Sleep in Other Animals


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Link : Le sommeil, une succession de cycles...

For most people, the length of their sleep cycles remains relatively constant, night after night, throughout their lives. Some people have 90-minute cycles, while others have cycles of 100, or 110, or 120 minutes, and so on.

People who need lots of sleep and people who need less sleep all get just about the same number of hours of deep non-REM sleep each night. Thus it is REM sleep and especially Stage 1 and Stage 2 non-REM sleep that vary the most from one person to another and that are curtailed in people who sleep fewer hours per night.


There are two main types of sleep, REM sleep and non-REM sleep, and non-REM sleep in turn is divided into four stages. But how are these various kinds of sleep distributed over the course of a night? In what order do they occur? Are they repeated several times?

By analyzing electroencephalograms (EEGs) of many nights of sleep, scientists have now been able to answer all these questions, because even though the relative importance and the duration of the various stages of sleep do vary from one individual to another and from one night to the next, and even though the sequence of these stages changes considerably from childhood through to old age, certain general patterns have been identified.

To better visualize these general patterns, researchers use a type of graph called a hypnogram. A hypnogram is nothing more than a minute-by-minute graphic record of a night’s sleep, as captured by an EEG. The hypnogram thus shows not only the sequence in which the various stages of sleep occur, but also the times at which each stage starts and ends.

If we analyze a typical hypnogram such as the one shown below, we see that a few minutes after falling asleep, we slip deeper and deeper into non-REM sleep: first into light non-REM sleep (Stages 1 and 2), and then into deep non-REM sleep (Stages 3 and 4).

Another striking feature of the hypnogram is the recurrent cycles in which the various stages of sleep follow one another, somewhat like a series of waves: 1-2-3-4-3-2-1-REM-1-2-3-4-3-2-1-REM, etc. Thus each descent into deep non-REM sleep is followed by a climb back up directly into a period of REM (or paradoxical) sleep.

The “train” of a night of sleep comprises many “cars” that are linked to one another in a specific order to form 4 or 5 major cycles.

Each cycle lasts about 1.5 to 2 hours, and a person thus goes through 4 or 5 of these cycles in one night’s sleep. Such cycles are described as “ultradian rhythms”, in contrast to the longer circadian rhythms, which have a period of about 24 hours.

The hypnogram also shows that deep non-REM sleep (Stages  3 and 4) is deepest in the earlier part of the night. This explains the great physically restorative powers associated with the first few hours of sleep. Toward the end of the night, the pattern reverses, and REM sleep, the kind of sleep generally associated with dreaming, becomes predominant.


Experience : Sleep and Dreaming Experiments
Original modules
Tool Module: Lucid Dreaming Lucid Dreaming

Recent Studies on the Role of Sleep

We all dream every night, even if we don’t remember our dreams. Memories of dreams are very unstable and disappear within a few minutes after we wake up. But it’s relatively easy to remember your morning dreams, either by writing them down as soon as you wake up, or by repeating their content to yourself so that they leave a trace in your long-term memory.

The worries that we experience during the day are often incorporated into our dreams. U.S. psychologist Rosalind Cartwright studied a large number of individuals who were going through divorces, and she found that when these people were awakened from REM sleep, most of the dreams that they reported dealt with their marital concerns.

In experiments that he conducted in the 1960s using cats, French neurobiologist Michel Jouvet succeeded in destroying the part of the brain that is responsible for the generalized absence of muscle tonus during REM sleep. This operation did not affect REM sleep in any other way; it continued normally, except that the cats’ muscles could now contract. What happened then? With the inhibition on their muscle movements removed, when the cats entered REM sleep, they would raise their heads, get up, and arch their backs, clean themselves, or stalk imaginary prey! In short, they engaged in the usual behaviours that characterize their species when awake.

At the time, Jouvet had concluded that the cats were “living their dreams”, and he thus associated REM sleep with dreaming. But more recent findings have raised questions about this interpretation.


Since ancient times, dreams have often been regarded as divine messages. With the work of Freud in the early 20th century, dreams came to be seen as the “royal road to the unconscious”. In the Freudian view, we construct the plots for our dreams both from impressions that we have gathered in the course of the day and from older memories that have been transformed or disguised to escape the control of our conscious minds.

It was not until some 50 years later, with the discovery of REM (paradoxical) sleep in 1953, that dreams were first associated with an observable physical state of the brain.


Henri Rousseau (1844-1910),
The Dream, 1910;
Oil on canvas, 6’8½” x 9’9½";
The Museum of Modern Art, New York.

The decisive experiment that established this connection was conducted by Nathaniel Kleitman and Eugene Aserinsky, the two U.S. physiologists who had discovered REM sleep. Their experimental protocol was quite simple: when the human subjects who were sleeping in their laboratory displayed the rapid eye movements typical of REM (paradoxical) sleep, the researchers woke them up and asked them whether they had just been dreaming. Some 75 to 95% of the subjects answered that they had indeed been dreaming, and were able to recount vivid dreams whose content was often fantastic, filled with all kinds of details and emotions.

This discovery received huge attention, because it was the first time that anyone had made an association between quantifiable states of REM sleep and what people experience subjectively as dreams.

But the mystery of dreams was still far from solved, because there were still some 5 to 10% of subjects who, though awakened from stages of non-REM sleep rather than REM sleep, nevertheless said that they had been dreaming. This percentage was even higher–as high as 70%–when instead of asking the subjects “Have you been dreaming?”, the researchers simply asked them “What was passing through your mind?” The states that the subjects reported in these cases were like sensory impressions similar to the dreams of REM sleep, but of shorter duration and with a more concrete, logical structure.

Thus REM sleep is not necessary for dreaming. A certain kind of dream (one involving surprising juxtapositions) does seem to be closely associated with REM sleep, but dreaming and REM sleep are in no way synonymous. This distinction between dreaming, which is a subjective state, and REM sleep, which is a state of the brain, is fundamental. In other words, dreaming is a phenomenon that can be described only qualitatively, by the dreamer himself or herself, in an account that often involves some distortions, whereas REM sleep can be subjected to precise physiological measurements, in particular by means of its EEG trace.

Scientists are learning more and more about the conditions for the occurrence of dreams and about their intrinsic characteristics, but not about their purpose. In fact, we still know almost nothing about the functions that dreams serve, and there are almost as many hypotheses about why people dream as there are scientists doing dream research.


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Lien : You Can Learn to Fall Asleep, Stay Asleep, & Wake Up Refreshed With Sleep School! Lien : The Ultimate Guide to Drowsy Driving  

A neuroscientist gets drunk to explain alcohol’s effects on the brain

It turns out that counting sheep isn’t really that much of a help in falling asleep–it’s more of a distraction.


There are plenty of stories about people who went several days without any sleep. In 1959, a disc jockey in New York stayed awake for a week as a fundraising stunt for a charity. The researchers who monitored him closely during this experiment found that he soon began to have hallucinations, and then became so paranoid that he refused to answer their questions.

Dr William C. Dement, an important sleep researcher, used himself as the subject of a sleeplessness experiment. After 48 hours without sleep, he confirmed that he was experiencing feelings of paranoia and suspiciousness toward his roommates. Very soon, he also experienced problems with his vision, as well as being unusually distracted and clumsy.

But the longest documented voluntary period of sleeplessness involved a 17-year-old male from California who went 264 hours (11 days!) without sleeping. He did so on a bet, and he did not use any stimulants to accomplish this feat. When he was done, he slept like a rock for 15 hours, and after a few more nights of sound sleep, he was as good as new.

Link : The Phenomena of Human Sleep

Driving when you haven’t had enough sleep is definitely a bad idea. In the United States, an estimated 56 000 highway accidents per year, involving some 1 500 fatalities, are believed to be caused by drivers who have fallen asleep at the wheel.

If you’re feeling sleepy while you’re driving, turning on the radio and opening your window will rarely suffice to keep sleep at bay. The best thing to do is stop your car on the side of the road and take a 15 to 20-minute nap. Drinking a cup of coffee may also help for a few hours, but coffee needs about 30 minutes to take effect. Thus one good way to refresh yourself a bit for the road is to drink a cup of coffee, then take that nap while you wait for the coffee to kick in.

Link : Countermeasures to Prevent a Fall-Asleep Crash While DrivingLink : Drowsy drivingLink : CaffeineLink : Somnolence au volant… connaissez-vous les risques ?

Sleep restriction therapy is a behavioural approach to treating insomnia. For example, suppose you’re sleeping only 6 hours per night because it’s taking you 2 hours to fall asleep. In this form of therapy, you would let yourself stay in bed for a total of only 6¼ hours. So if you always got up at 7:00 AM, you wouldn’t let yourself go to sleep until 12:45 AM. This restriction would help you to short-circuit the idea of performance associated with sleep, while aggravating your sleep deprivation very slightly. After a few nights of such treatment, people who have been experiencing insomnia often fall asleep in less than 15 minutes. They then gradually lengthen the amount of time that they stay in bed, by 15 minutes each week, until eventually they are getting a reasonable night’s sleep.


People are too quick to label others as lazy if they accord a lot of importance to their sleep. When we’re short of time, our hours of sleep are often one of the first things we let go. But if there’s one thing for which we should show more respect, it’s our need for a good night’s sleep.

To understand the importance of sleep, simply consider what happens to people who don’t sleep enough (or, as the medical profession might put it, people who show signs of sleep deprivation syndrome). Obviously, these people feel sleepy during the daytime. They may also tend to “sleep in” on the weekend to pay back their “sleep debt”.

If they don’t manage to pay back this debt, they will suffer several harmful consequences. First, they’ll be less alert, and their ability to think and concentrate will be diminished. Next, their reflexes will slow, and they will experience memory disorders, muscle fatigue, and mood swings, and even display aggressive behaviour and have difficulty in situating themselves in time or space. They may also experience hallucinations similar to those that most people experience when falling asleep, midway between reality and dreaming. Such hallucinations are harmless when you’re in bed, but can be fatal if you’re at work or at the wheel (see sidebar). In fact, it is believed that lack of sleep may be the hidden cause behind most of the “human error” that causes accidents.

In the longer term, several studies have found, there is a relationship between insufficient quantity and quality of sleep and a number of chronic health problems, including obesity, diabetes, and high blood pressure. In these three cases, the lack of sleep disturbs regulatory mechanisms that are normally at work during the night.

Lack of sleep may be voluntary or involuntary. You may cut back on your hours of sleep voluntarily when you work too far into the night, or when you stay up late to pursue more entertaining nocturnal activities. But lack of sleep can also be involuntary, when you try to sleep but can’t manage to do so–in other words, when you experience insomnia.

Insomnia often sets in insidiously. Suppose, for example, that at first you lose a few nights because you’re worrying about having lost your job, or about your daughter’s marital problems. After a few nights, when you go to bed, you might also start worrying about whether you’ll be able to fall asleep. These worries might be bad enough that they will in fact make it harder for you to sleep. Having had yet another bad night’s sleep, you’d go to bed even more worried the next night, and the vicious cycle of insomnia would be well under way.

More than half of all people with insomnia can obtain some relief, if not a complete cure, by simply applying the following recommendations for healthy living, which involve changes both in attitudes and in habits. This “sleep re-education” approach can be summarized as follows.


- If you can’t sleep, don’t blame yourself . Putting pressure on yourself only makes it that much harder to sleep.

- If you sleep less than 8 hours, don’t assume that means you’re not getting enough sleep. It’s counterproductive to expect to fall asleep when your head hits the pillow and then sleep 8 hours straight every night. 

- Don’t let yourself get too upset about the situation.

- If you get a bad night’s sleep, try to plan a pleasant activity when you start your day. That way, you won’t get bogged down brooding about your sleep habits, and you’ll prove to yourself that you can have a good day even if you haven’t slept well.



- Wait for the right time to go to bed; do so only when you feel very tired. If you don’t fall asleep after 15 or 20 minutes, get up and get out of your bedroom.

- Use your bed only for sleep or sex. Take the TV, reading materials, and the telephone out of your bedroom. The idea is to create strong mental associations between this room and sleeping.

- Make your biological clock more regular by trying to get up at the same time every morning (even on weekends) regardless of how many hours of sleep you got the night before.

- If you suffer from insomnia, don’t take any naps during the daytime. Also, don’t engage in any intense exercise, take a hot bath, or eat a heavy meal just before going to bed, because all of these activities raise your body temperature, which makes it harder to fall asleep. Do, however, take a lukewarm bath or shower, because that relaxes your muscles, which can help you to sleep.

- Avoid tea, coffee, cola drinks, tobacco, alcohol, and other stimulants before going to bed.

- Eat an evening meal, neither too light nor too heavy, and not too close to bedtime. Dairy products and some herbal teas may also help you to sleep.

- Regular, moderate physical exercise, not too close to bedtime, also helps you to sleep. It can be something as simple as an evening walk through your neighbourhood.

- Instead of worrying about whether you’ll be able to fall asleep, try to develop some relaxing new habits associated with bedtime–reading or writing a bit, for example–because they too can help you to sleep.

- Doing relaxation exercises can help relieve tension that may be keeping you from falling asleep. Breathing calmly and deeply, or listening to soothing music, will help you to relax. Anything that calms you down and alleviates stress and anxiety is conducive to sleep.

Compared with sedatives, this sleep re-education approach does a more effective job of modifying sleep habits permanently. When people’s insomnia persists, taking sedatives for a few days can help them get back into the habit of sleeping. But sedatives are only a temporary solution, and a very imperfect one, because they can quickly create a dependency, so that within a few weeks, they become an integral part of the problem.

Most sedatives work by binding to GABA receptors in the brain. In so doing, they inhibit the wakefulness network, but they also disturb other circuits, such as those for mood and memory. Also, sedatives often have side effects, such as tremors, or sleepiness during the daytime. Thus the real solution is to re-learn how to sleep.

A 20-minute nap would do most people good, because it would make them more alert and improve their ability to concentrate. The psychological benefits in terms of their mood would also be appreciable. But be careful: if you nap for too long (say, an hour), you will go into too deep a sleep, so you’ll feel sluggish for a while after you wake up.

Naps are recommended for people who have accumulated a sleep deficit, for people who are sleepy, and for people who suffer from certain sleep disorders, such as narcolepsy. But naps are not recommended for people with insomnia, because they can wind up “borrowing” from their next night’s sleep.

Research has shown that in extreme cases, such as when people have to drive alone and cannot get several hours of sleep in a row, taking 10-to-20-minute naps at regular intervals over the course of the day can partly meet their need for sleep and enable them to perform at minimally acceptable levels for a few days. But their performance under these conditions will always be far poorer than if they were completely rested.

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People who are performing monotous tasks such as driving a vehicle for hundreds of kilometres may experience "micro-naps" that last a few seconds. The frequency of these micro-naps is proportional to the individual's sleep deficit, but they can also occur in people who have gotten enough sleep, especially during cyclical variations in alertness, such as those that occur about once every 90 minutes.

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