Sleep Basics - 101 Questions About Sleep and Dreams

Chapter 1 - Normal Sleep

1. What is sleep?
2. Why do we sleep?
3. How much sleep should I get?
4. Is it true that we need less sleep as we get older?
5. What is yawning?
6. What about bedroom temperature and sleeping position? Can these things affect sleep?
7. Can we make up for lost sleep?
8. Are there any advantages in taking a nap?
9. Does meditation change sleep?
10. Can we learn during sleep?
11. Do we dream during our deepest sleep?
12. Do people in other countries and cultures sleep differently?
13. Does your body size affect your sleep?
14. What are the best ways for most of us to get a good night's sleep?

1. What is sleep?

Sleep is a behavioral state characterized by little physical activity and almost no awareness of the outside world. Most scientists think that sleep does something important -- something vital for life, although research has not yet identified the purpose for sleep. Nevertheless, we all know when we need to sleep -- we can feel this need. We also know when sleep has done its work -- we feel rested and that we have slept enough. Another important feature of normal sleep is that it can end quickly. Although a sleeper may appear to be unconscious; unlike someone who is actually knocked-out, anesthetized or in a coma; a sleeping person can be easily awakened and can resume normal waking activity within a minute or two.

Sleep is an active, highly organized sequence of events and physiological conditions. Sleep is actually made up of two separate and distinctly different states: 'non-rapid eye movement sleep' (NREM sleep) and 'rapid eye movement sleep' (REM sleep) or dreaming sleep. The NREM and REM types of sleep are as different from one another as both are different from wakefulness.

NREM sleep is further divided into stages 1 - 4 based on the size and speed of the brain waves generated by the sleeper. Stages 3 and 4 of NREM sleep have the biggest and slowest brain waves. These big, slow waves are called delta waves and stages 3 and 4 sleep, combined, are often called 'slow-wave sleep' or 'delta sleep'.

During REM sleep you can watch the sleeper's eyes move around beneath closed eyelids. Some scientists think that the eyes move in a pattern that relates to the visual images of the dream. We are almost completely paralyzed in REM sleep -- only the heart, diaphragm, eye muscles and the smooth muscles (such as the muscles of the intestines and blood vessels) are spared from the paralysis of REM sleep.

Doctors have tried to determine what type of sleep is the deepest sleep. To do this, they measure how much noise or other alerting stimulation is required to awaken a sleeper from the various types of sleep. It is always possible to awaken someone who is sleeping, as opposed to, say, someone who is in a coma. However, people in stages 3 and 4 sleep require the most stimulation to awaken. Therefore, this phase of sleep is often thought of as 'deep sleep'. Also, large spurts of growth hormone are secreted during stages 3 and 4 NREM sleep. Consequently, these stages of sleep are thought to restore the body from the wear and tear of waking activity. People in REM sleep also tend to be quite difficult to awaken, but this finding is variable -- sometimes even the slightest noise can awaken a person in REM sleep. Nevertheless, because it is often difficult to awaken a person from REM sleep, many doctors think also of REM sleep as a 'deep' phase of sleep.

There are many theories about the function of REM sleep and dreaming -- ranging from 'safe, socially acceptable, wish fulfillment' to 'consolidation of memories' to 'providing necessary stimulation to the entire nervous system during development'. Researchers used to think that REM sleep was necessary for normal psychological function, because experimental REM deprivation caused some subjects to behave strangely. The notion that we need REM sleep for our mental health is not accepted now, because, among other reasons, people have uneventfully withstood long and almost complete REM deprivation. Some experiments have shown that REM deprivation improves depression. However, REM sleep must still do something, because rats will die after 2 - 3 weeks if they are deprived of REM sleep by a special experimental computer that wakes them up each time REM sleep is achieved. Whatever REM sleep does, it is clear that every aspect of existence from the body's manufacture of proteins to sexual arousal, including orgasm, is influenced by REM sleep. It is likely that the ultimate explanation of REM sleep will be very broad -- not simply focused on one physiologic function.

The chart below is called a hypnogram. Hypnograms are made to summarize sleep laboratory recordings. This particular hypnogram shows how a typical night's sleep for a young, healthy adult is organized. Notice how the night is structured into the various stages of NREM sleep alternating with REM sleep, with most slow-wave sleep occurring in the first part of the night and most REM sleep occurring in the last part.

2. Why do we sleep?

We sleep because we get sleepy and we cannot work if we get too sleepy. That is the simplest and yet the most profound answer to this question. The scientific truth is, however, that we do not yet know why we get sleepy. We know that all mammals as well as some birds and reptiles sleep. Many doctors think sleep comes in order to get rid of certain chemicals that build up in our bodies during the day's activities. Brain research in the 1960's and 1970's has identified several molecules involved in cell-to-cell communication within the brain as being important for sleep. More recent work has isolated products of the body's immune system that seem to be sleep-inducers.

However, feeling sleepy is not the whole story. Some timing mechanism is also involved. We know that every living thing composed of cells with a nucleus has a daily cycle of activity and inactivity (if not actual wakefulness and sleep). The timing and control of the wakefulness-sleep cycle depends on one or more biological clocks in our bodies. These clocks are sensitive to light and have evolved over the ages in close approximation to the 24-hour light-dark cycle of our world. Thus, sleep seems to be an unavoidable part of human behavior. In humans, sleep is physiologically programmed to come each day, either in one long bout (about 6 - 8 hours each night) or in two shorter bouts (a 5 - 6 hour sleep at night and a 1 - 2 hour nap in the afternoon). The timing of sleep and wakefulness is controlled to a great extent by our exposure to the natural light and dark cycles of the earth. All humans tend to sleep in the dark and move about in the light. It takes the human body several days to change to a different light-dark schedule such as when one flies from New York to New Dehli. In fact, the influence of light on the timing of sleep is so powerful that doctors are now using exposure to bright light as a treatment to reset the sleep clock of people who have somehow disrupted their schedule.

In the extreme, sleep does seem to be necessary for life. Experimental rats die if they are completely deprived of sleep for longer than 1 - 4 weeks. However, do not worry. The experimental deprivation was done by means of special computers and alarm systems -- it is not possible for even the poorest of human sleepers to lose so much sleep that life is threatened.

3. Q: How much sleep should I get?

There is no 'normal' amount of sleep. The average amount of sleep for adults is 7 - 8 hours. But the range of nighttime sleep duration must be expanded to between 6 - 9 hours in order to include the large majority of people. Therefore, a few people feel fine with as little as 5 hours of sleep, while others require more than 10 hours to feel refreshed and alert throughout the day. The amount of sleep you need is that optimum amount which allows you to function throughout the day without feeling drowsy when you sit quietly and try to pay attention to something.

We cannot, for very long, force ourselves to sleep much less or much more than this optimum amount. Several nights of sleeping an hour less than our usual amount will leave us sleepy and ineffective in the day. Conversely, several nights of staying in bed and trying to sleep an hour more than our optimum amount will leave us sleeping poorly with more awakenings -- particularly in the early morning. Doctors believe that the optimum amount of sleep each person needs to remain alert during the day is biologically different from person to person. To a great degree, our optimum sleep need is determined by heredity. Scientists have found, for instance, that strains of mice can be selectively bred to sleep considerably more or considerably less than the average mouse.

4. Q: Is it true that we need less sleep as we get older?

Probably not. It seems that during infancy and in adolescence there are increases in sleep need, perhaps brought on by developmental changes. However, the best research available indicates that healthy elderly people sleep about as much as they did when they were young adults. The common belief that the elderly sleep less probably comes from the fact that elders often have medical conditions that interfere with their sleep. This is why most elderly people are 'light sleepers' at night, yet they frequently dose-off during the day.

This type of light sleep and dozing pattern is what sleep researchers would expect if a person is awakened again and again while they try to sleep. In fact, research on repetitive sleep disruption, called 'sleep fragmentation', has shown that the rate of sleep disruptions determines whether or not the sleep is felt to be satisfactorily restorative, and whether or not there is proper alertness the next day. These kinds of studies show that disruptions every minute will greatly reduce the restorative value of sleep. However, disruptions every five minutes will affect restoration much less -- even when total sleep time is the same for the one-per-minute and five-per-minute rates of disruption. Thus, scientists believe that for refreshing sleep, it is not just the total amount of sleep that is important. Sleep must be continuous as well.

5. Q: What is yawning?

Most vertebrate animals exhibit yawning. A yawn consists of widely opening the mouth with a slow inspiration at the beginning and a quick expiration at the end. Yawning is a reflex behavior that can be only partially controlled by our own volition. The behavior occurs most often when we feel sleepy, bored, and, perhaps, physically fatigued. Yawning can also be triggered by drugs and has been used as a medical index because there are changes in the frequency of yawning in certain disease states. Scientists have not identified a function of yawning, but, at least in humans, it does seem to be contagious since observers are more likely to yawn when they watch someone else yawn. In this sense, yawning is a type of social behavior that is largely involuntary and controlled by the brain.

6. Q: What about bedroom temperature and sleeping position? Can these things affect sleep?

People sleep best when they are comfortable, physically and mentally. There is no universal formula for physical and mental comfort. It is best to explore bedroom temperature, mattress, bedclothes, etc. until you find bedroom conditions under which you feel that you sleep the best.

Similarly, there is no single ideal sleeping position. Most people move through many sleeping postures in the course of a normal night's sleep. Scientists think such movement is good because it prevents pressure-related restriction of circulation. However, conditions such as pregnancy, arthritis and other medical conditions will obviously exclude certain sleeping positions with no ill effects. Furthermore, avoiding some sleeping postures can be helpful. For example, people with breathing problems associated with airway obstruction breathe irregularly and sleep poorly when lying on their backs. Such people often sleep sitting-up as a matter of preference until the condition is effectively treated.

7. Q: Can we make up for lost sleep?

Yes, we can make up for lost sleep, but only to a certain extent. Suppose a man, who usually sleeps 7 hours a night, loses 2 nights of sleep. He will not sleep 21 hours (14 hours longer than usual) on the third night, when he is able to sleep. After significant sleep loss, we may have more slow-wave sleep for the next couple of nights, but we rarely sleep more than 2 - 4 hours longer than usual. This is because our wakefulness-sleep cycle depends on both our sleep need and our internal timing mechanisms. Furthermore, experiments with shift work have shown that people who stay awake for a single night and then go to bed at 8 AM, instead of their usual 11 PM, will not simply move their normal sleep to an interval 9 hours later. Rather, their sleep beginning at 8 AM will be shorter and more broken because it is occurring at a biological time when activity usually occurs. This inability to sleep during certain periods of the day is due to the alerting influences of the biological clock located in the brain's hypothalamus. What our ancestors previously thought of as a 'second wind', is now understood by sleep scientists as clock-dependent alerting. It is because of complex interplay between sleep deprivation and clock dependent alerting, that sleep losses or shifts in sleep time will have effects for several days.

The figure illustrates this interplay and shows over a period of 48 hours, a two-peak pattern for each day. There is a period with markedly increased sleep tendency in the early morning hours between 3 and 6 AM and a smaller but reliable afternoon peak between 1 and 3 PM. This is the so-called siesta effect or afternoon slump. Both periods of increased sleep tendency can be exaggerated by sleep promoting factors such as alcohol consumption and sleep deprivation. Errors and reduced productivity peak at the times of maximum sleep tendency.

8. Q: Are there any advantages in taking a nap?

Certain cultures use the siesta very successfully. However, siesta cultures are relatively consistent in napping. In most western cultures, napping is not consistent day after day. If you want to nap, nap at the same time each day and for the same duration, particularly if you are prone to insomnia. Many people complain about Sunday-night insomnia. What usually happens in these cases is that the person napped on Sunday from, say, 2 to 5 in the afternoon and then could not get to sleep at the usual time Sunday night. That is why keeping a consistent schedule is the best strategy.

With respect to occasional napping, one important advantage is that even a 30 - 60 minute nap greatly helps a person counter sleep loss. Studies have shown that the first hour or so of sleep is most potent in relieving the effects of missing a night's sleep.

9. Q: Does meditation change sleep?

Meditation probably will not affect sleep in any significant way. In its most common forms, meditation involves the practice of sitting in some prescribed position with the eyes closed and 'saying' (either audibly or only mentally) a prescribed word or set of words, called mantras. There are a variety of meditation techniques that are taught by trained individuals for the purpose of improving waking functioning as well as spiritual and physical well-being. These meditation techniques are also claimed to have various effects on sleep such as 'improving sleep', 'reducing the need for sleep' and being an 'alternative to sleep'. However, scientific studies on meditators have found that most meditation is characterized by the brain wave pattern of quiet, relaxed wakefulness with occasional bouts of NREM sleep. Thus, the best current studies suggest that any meditation-related shortening of nocturnal sleep probably occurs because the meditator is getting daytime sleep (i.e. is napping) during the act of meditation. There is no evidence that meditation will reduce a person's overall need for sleep.

10. Q: Can we learn during sleep?

No. There is no study that shows efficient learning during sleep. The brain needs to be awake in order to learn, as learning is usually defined. When new information is presented to someone while they sleep, the amount of information that they remember the next morning depends on how long and how many times they were awake during the night -- not on how well they slept.

11. Q: Do we dream during our deepest sleep?

The answer is yes, but only partially yes. The experience which we would all agree constitutes dreaming involves a good deal of action and several senses such as vision, hearing and touch. This type of experience occurs most often in REM sleep.

Here is why the answer is only partially yes: First, some dreamlike experiences can occur during other phases of sleep besides REM sleep. Second, REM sleep cannot really be considered our 'deepest sleep'. The depth of a particular phase of sleep is best defined in terms of how difficult it is to awaken someone when they are in that particular phase of sleep. What phase of sleep requires the loudest noise, for example? The two phases of sleep that are 'deepest' -- that is the hardest to wake up from -- are 'slow wave sleep' (stages 3 and 4 of NREM sleep combined, is called 'slow wave sleep' because of the big, slow brain waves seen then) and REM sleep. Dreams rarely occur in slow wave sleep and frequently occur in REM sleep.

12. Q: Do people in other countries and cultures sleep differently?

The basic physiology of human sleep does not seem to vary much from race to race or culture to culture. However, there are effects of culture and climate. For example, many equatorial cultures have the institution of an afternoon siesta which breaks sleep into a short afternoon bout and a longer nighttime bout. People in siesta cultures seem to sleep about the same amount as those in other cultures. There also are studies showing profound seasonal changes in sleep. The largest seasonal changes occur in the polar regions, where there are great changes over the year in the length of the light interval in the day with long light periods increasing the tendency for the daily schedule to have two sleep bouts.

13. Q: Does your body size affect your sleep?

There seems to be no direct effect of body size on sleep. Assuming that the length and width of the sleeping surface is of appropriate dimensions, small people sleep just as much as, and just as well as, large people of comparable ages. However, if body size restricts the normal body movements during sleep or the ability of the diaphragm to move during respiration, such as is common with extremely overweight people, then sleep can be profoundly disturbed.

14. Q: What are the best ways for most of us to get a good night's sleep?

Here are ten sensible rules for a good night's sleep:

• Stick to a regular schedule of going to bed and getting up at the same time every day.
• Be consistent about taking naps: Take one every afternoon or none at all. People who take a nap once in a while usually find they do not sleep well that night.
• Exercise regularly in the morning or early afternoon, but do not engage in strenuous physical activity just before bedtime.
• Stay away from drinks containing caffeine after about 4 PM.
• Avoid alcohol after the dinner hour. Instead of promoting sleep, a nightcap actually disturbs sleep patterns and can cause early morning awakenings.
• Be careful about sleeping pills. Under most circumstances, these medications should not be taken for more than four weeks. Longer use leads to increased insomnia.
• Find the right room temperature for you and maintain it throughout the night.
• Try to relax before going to bed: Take a warm bath, read a light novel, listen to music, avoid stressful thoughts.
• Do not eat heavily just before going to bed.
• If you cannot sleep at night, do your best to preserve your usual 24-hour cycles of activity-rest and exposure to light and dark. For example, do not get up, turn on bright lights and read or exercise. It is best to remain reclining in the dark and listen to music or an audio book.

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