Unit 7. Sleep

Sleep covers a Man all over, Thoughts and all, like a Cloak; ’tis Meat for the Hungry, Drink for the Thirsty, Heat for the Cold, and Cold for the Hot.

Miguel de Cervantes Don Quixote

Introduction.

Sleep remains one of the great mysteries of modern neuroscience. We spend nearly one-third of our lives asleep, but the function of sleep still is not known. Fortunately, over the last few years researchers have made great headway in understanding some of the brain circuitry that controls wake-sleep states. Scientists now recognize that sleep consists of several different stages; that the choreography of a night’s sleep involves the interplay of these stages, a process that depends upon a complex switching mechanism; and that the sleep stages are accompanied by daily rhythms in bodily hormones, body temperature and other functions.

Sleep disorders are among the nation’s most common health problems, affecting up to 70 million people, most of whom are undiagnosed and untreated. These disorders are one of the least recognized sources of disease, disability and even death, costing an estimated $100 billion annually in lost productivity, medical bills and industrial accidents. Research holds the promise for devising new treatments to allow millions of people to get a good night’s sleep.

Exercise 1. What do you know about sleep?

1. What is sleep? What processes take place in human organism during sleep?

2. What processes take place in the human brain during sleep?

3. How long does sleep last? What stages does it include?

4. What sleep disorders do you know?

5. Are you an early bird or a night owl? What other sleep habits do you have?

Exercise 2. Is sleep primarily to benefit the body or the mind? Read the following text to find the answer.

Why Do We Sleep?

By C. Claiborne Ray

“Sleep has many functions, and most of us think the main functions are not for the body but for the brain,” said Dr. Arthur Spielman, a sleep expert at City College of New York. “But,” he added, “you are talking to a brain scientist, and it depends on whom you ask.’’

The reason sleep occurs in the first place is tied to both mental and physiological cycles that evolved on a planet with a 24-hour cycle of light and dark, Dr. Spielman said. The internal biological clocks that developed in living things, from single cells to humans, allow them to anticipate the transitions from light to dark and from dark to light, so that they are ready for the functions appropriate to light, like metabolism and photosynthesis, and for those suited to darkness. “A physiologist might say sleep was to avoid wasting metabolic energy in the dark,’’ he said. “But a brain scientist would say that glycogen, the only fuel for the brain, is depleted during waking and restored during sleep.”

Sleep is useful for restoring particular parts of the brain that are quiet during sleep and return to functioning during waking, like the areas involved in attention, alertness and memory. Sleep is also important for regulating the timing of hormones under the control of the brain, Dr. Spielman said, like cortisol, the stress-response hormone, which is suppressed at the beginning of sleep and ramps up in anticipation of waking, and growth hormone, which is secreted at night during sleep characterized by slow brain waves. (August 15, 2006 NY Times)

Exercise 3. Read the chapter about sleep taken from the book Brain Facts: a Primer on the Brain and Nervous System, 2002 to check your answers in Exercise 1.

The Stuff of Sleep

Sleep appears to be a passive and restful time when the brain is less active. In fact, this state actually involves a highly active and well-scripted interplay of brain circuits to produce the stages of sleeping.

The stages of sleep were discovered in the 1950s in experiments examining the human brain waves or electroencephalogram (EEG) during sleep. Researchers also measured movements of the eyes and the limbs during sleep. They found that over the course of the first hour or so of sleep each night, the brain progresses through a series of stages during which the brain waves progressively slow down. The period of slow wave sleep is accompanied by relaxation of the muscles and the eyes. Heart rate, blood pressure and body temperature all fall. If awakened at this time, most people recall only a feeling or image, not an active dream.

Over the next half hour or so, the brain emerges from the deep slow wave sleep as the EEG waves become progressively faster. Similar to during waking, rapid eye movements emerge, but the body’s muscles become almost completely paralyzed (only the muscles that allow breathing remain active). This state is often called rapid eye movement (REM) sleep. During REM sleep, there is active dreaming. Heart rate, blood pressure and body temperature become much more variable. The first REM period usually lasts ten to 15 minutes.

Over the course of the night, these alternative cycles of slow wave and REM sleep alternate, with the slow wave sleep becoming less deep, and the REM periods more prolonged, until waking occurs.

Over the course of a lifetime, the pattern of sleep cycles changes. Infants sleep up to 18 hours per day, and they spend much more time in deep slow wave sleep. As children mature, they spend less time asleep, and less time in deep slow wave sleep. Older adults may sleep only six to seven hours per night, often complain of early wakening that they cannot avoid, and spend very little time in slow wave sleep.

Sleep disorders

The most common sleep disorder, and the one most people are familiar with, is insomnia. Some people have difficulty falling asleep initially, but other people fall asleep, and then awaken part way through the night, and cannot fall asleep again. Although there are a variety of short-acting sedatives and sedating antidepressant drugs available to help, none of these produces a truly natural and restful sleep state because they tend to suppress the deeper stages of slow wave sleep.

Excessive daytime sleepiness may have many causes. The most common are disorders that disrupt sleep and result in inadequate amounts of sleep, particularly the deeper stages. These are usually diagnosed in the sleep laboratory. Here, the EEG, eye movements and muscle tone are monitored electrically as the individual sleeps. In addition, the heart, breathing, and oxygen content of the blood can be monitored.

Obstructive sleep apnea causes the airway muscles in the throat to collapse as sleep deepens. This prevents breathing, which causes arousal, and prevents the sufferer from entering the deeper stages of slow wave sleep. This condition can also cause high blood pressure and may increase the risk of heart attack. There is also an increased risk of daytime accident, especially automobile accidents, which may prevent driving. Treatment is complex and may include a variety of attempts to reduce airway collapse during sleep. While simple things like losing weight, avoiding alcohol and sedating drugs prior to sleep, and avoiding sleeping on one’s back can sometimes help, most people with sleep apnea require positive airway pressure to keep the airway open. This can be provided by fitting a small mask over the nose that provides an air stream under pressure during sleep. In some cases, surgery is needed to correct the airway anatomy.

Periodic limb movements of sleep are intermittent jerks of the legs or arms, which occur as the individual enters slow wave sleep, and can cause arousal from sleep. Other people have episodes in which their muscles fail to be paralyzed during REM sleep, and they act out their dreams. This REM behavior disorder can also be very disruptive to a normal nights’ sleep. Both disorders are more common in people with Parkinson’s disease, and both can be treated with drugs that treat Parkinson’s, or with an anti-epileptic drug called clonazepam.

Narcolepsy is a relatively uncommon condition (one case per 2,500 people) in which the switching mechanism for REM sleep does not work properly. Narcoleptics have sleep attacks during the day, in which they suddenly fall asleep. This is socially disruptive, as well as dangerous, for example, if they are driving. They tend to enter REM sleep very quickly as well, and may even enter a dreaming state while still awake, a condition known as hypnagogic hallucinations. They also have attacks during which they lose muscle tone, similar to what occurs during REM sleep, but while they are awake. Often, this occurs while they are falling asleep or just waking up, but attacks of paralysis known as cataplexy can be triggered by an emotional experience or even hearing a funny joke.

Recently, insights into the mechanism of narcolepsy have given major insights into the processes that control these mysterious transitions between waking, slow wave and REM sleep states. (From Brain Facts: a Primer on the Brain and Nervous System, 2002)

Exercise 4. Work in small groups. Write out from the text 15 key word combinations which will help you to retell the text and explain your choice. Then together agree on the final list of word combinations.

Exercise 5. In the following text the paragraphs are mixed. Put them in the correct logical order. The first and the last paragraphs are in their right places.

How long can humans stay awake?

J. Christian Gillin, a professor of psychiatry at the University of California, San Diego, conducts research on sleep, chronobiology and mood disorders. He supplies the following answer.

(А) The easy experimental answer to this question is 264 hours (about 11 days). In 1965, Randy Gardner, a 17-year-old high school student, set this apparent world-record for a science fair. Several other normal research subjects have remained awake for 8 to 10 days in carefully monitored experiments. None of these individuals experienced serious medical, neurological, physiological or psychiatric problems. On the other hand, all of them showed progressive and significant deficits in concentration, motivation, perception and other higher mental processes as the duration of sleep deprivation increased. Nevertheless, all experimental subjects recovered to relative normality within one or two nights of recovery sleep. Other anecdotal reports describe soldiers staying awake for four days in battle, or unmedicated patients with mania going without sleep for three to four days.

(B) The more difficult answer to this question revolves around the definition of "awake." As mentioned above, prolonged sleep deprivation in normal subjects induces altered states of consciousness (often described as "microsleep"), numerous brief episodes of overwhelming sleep, and loss of cognitive and motor functions. We all know about the dangerous, drowsy driver, and we have heard about sleep-deprived British pilots who crashed their planes (having fallen asleep) while flying home from the war zone during World War II. Randy Gardner was "awake" but basically cognitively dysfunctional at the end of his ordeal.

(C) In the case of rats, however, continuous sleep deprivation for about two weeks or more inevitably caused death in experiments conducted in Allan Rechtschaffen’s sleep laboratory at the University of Chicago. Two animals lived on a rotating disc over a pool of water, separated by a fixed wall. Brainwaves were recorded continuously into a computer program that almost instantaneously recognized the onset of sleep. When the experimental rat fell asleep, the disc was rotated to keep it awake by bumping it against the wall and threatening to push the animal into the water. Control rats could sleep when the experimental rat was awake but were moved equally whenever the experimental rat started to sleep. The cause of death was not proven but was associated with whole body hypermetabolism.

(D) In certain rare human medical disorders, the question of how long people can remain awake raises other surprising answers, and more questions. Morvan’s fibrillary chorea or Morvan’s syndrome is characterized by muscle twitching, pain, excessive sweating, weight loss, periodic hallucinations, and severe loss of sleep (agrypnia). Michel Jouvet and his colleagues in Lyon, France, studied a 27-year-old man with this disorder and found he had virtually no sleep over a period of several months. During that time he did not feel sleepy or tired and did not show any disorders of mood, memory, or anxiety. Nevertheless, nearly every night between 9:00 and 11:00 p.m., he experienced a 20 to 60-minute period of auditory, visual, olfactory, and somesthetic (sense of touch) hallucinations, as well as pain and vasoconstriction in his fingers and toes. In recent investigations, Morvan’s Syndrome has been attributed to serum antibodies directed against specific potassium (K+) channels in cell and nerve membranes.

(E) Another rare disorder, Fatal Familial Insomnia (FFI), is an autosomal dominate disease that is invariably fatal after about six to 30 months without sleep. FFI is probably misnamed because death results from multiple organ failure rather than sleep deprivation. The pathological processes include degeneration of the thalamus and other brain areas, over-activity of the sympathetic nervous system, hypertension, fever, tremors, stupor, weight loss, and disruption of the body's endocrine systems. FFI belongs to a class of infectious prion diseases that include Mad Cow Disease.

(F) To return to the original question, "How long can humans stay awake?" the ultimate answer remains unclear. Despite the rat studies in Chicago, I am unaware of any reports that sleep deprivation per se has killed any human (excluding accidents and so forth). Indeed, the U.S. Department of Defense has offered research funding for the goal of sustaining a fully awake, fully functional "24/7" soldier, sailor, or airman. Future warriors will face intense, around-the-clock fighting for weeks at a time. Will bioengineering eventually produce genetically-cloned soldiers and citizens with a variant of Morvan’s syndrome who need no sleep but remain effective and happy? I hope not. A good night’s sleep is one of life’s blessings. As Coleridge wrote years ago, "Oh sleep! It is a gentle thing, beloved from pole to pole," and Wilse Webb, a prominent sleep researcher, more recently called sleep the gentle tyrant: It can be delayed but not defeated.

Exercise 6. Are the following statements true or false, according to the text? Explain your answer.

1. A healthy person can survive without sleep no more than three days.

2. Sleep deprivation damages normal functioning of the organism.

3. Prolonged sleep deprivation produces no negative effect on health.

4. Sleep disorders may be a symptom of serious diseases.

5. Sleep disorders can be inherited.

6. Research of sleep has serious implications for economy and industry.

Exercise 7. Would you like to be able to live without sleep? Why? Why not?

Exercise 8. Summarize everything you know about sleep, its functions and sleep disorders into one report.