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Beliefs, Theories, And Scientific Observations Of Sleep, Biological Determinants Of Sleep, Stages Of SleepWhy we sleep and how it is triggered, The structure of sleep

Sleep is a state of physical inactivity and mental rest in which conscious awareness, thought, and voluntary movement cease and intermittent dreaming takes place. This natural and regular phenomenon essential to all living creatures normally happens with the eyes closed and is divided into two basic types: REM (rapid eye movement) and NREM (non-rapid eye movement) sleep. As passive as sleep appears, it is actually a very active and deliberate process in which the brain busily turns off wakeful functions while turning on sleep mechanisms. No one knows exactly why we must sleep or how it happens, but the quality, quantity, and type of sleep impacts the quality, quantity, and effectiveness of our wakeful mental and physical activities. These, in turn, influence the quality, quantity, and timing of sleep.

Enforced sleep-deprivation experiments

In the attempt to understand our need for sleep, experiments in sleep deprivation play an important role. Total sleep deprivation longer than 40 hours proves impossible, however, due to brief, totally unpreventable periods of "microsleep" which will happen even during physical activity. These microsleeps barely last a few seconds, but they may explain performance lapses in waking activities. They demonstrate the body's obvious need for sleep and may even have some restorative function.

While sleep deprivation can eventually cause death, sleep deprivation lasting up to ten days shows no serious, prolonged consequences and does not cause severe psychological problems or mental illness as once thought. In 1965, for example, 17-year-old Randy Gardner decided to attempt a new world record for total sleep deprivation as his high school science fair project. He succeeded in staying awake for an incredible 264 hours. When researchers and psychiatrists from Stanford University heard of Gardner's experiment, they rushed to the scene and monitored his progress. On the last night, one researcher took Randy to an arcade to keep him awake. Randy won every game, indicating that prolonged sleep deprivation did not seriously impair his physical or psychomotor functioning. After his extraordinary vigil, Randy slept just 14 hours and 40 minutes, awoke naturally around 10:00 p.m., stayed awake 24 hours, and slept a normal eight hours. Follow-up over the years has shown that Gardner suffered no adverse effects from his experience.

Losing more than one night's sleep does produce a noticeable increase in irritability, lethargy, disinterest, and even paranoia. While not seriously impaired, psychomotor performance and concentration are adversely affected. While autonomic (involuntary) nervous system activity increases during sleep deprivation to keep heart rate, blood pressure, breathing, and body temperature normal, physical fitness cannot be maintained and immunological functions seem to suffer.

Measurement of electrical impulses in the sleeping brain

The greatest contribution to sleep study was the development of the EEG, or electroencephalogram, by German psychiatrist Hans Berger in 1929. This electrode, attached to the scalp with glue, records electrical impulses in the brain called brain waves. The discovery triggered investigations into sleep in major centers around the world. Specific brain wave patterns became evident and sleep was generally classified into distinct stages.

In 1953, Professor Nathaniel Kleitman and his graduate student Eugene Aserinsky reported their close observations of a sleep stage they called REM-rapid eye movement. An electro-oculogram, or EOG, taped close to the eyelids, recorded both vertical and horizontal eye movement, which became rapid and sporadic during REM sleep. The electromyogram, or EMG, recorded chin and neck muscle movement which, for as yet undetermined reasons, completely relaxed during REM sleep. Kleitman and Aserinsky found that when subjects were awakened from REM sleep they almost always reported a dream, which was seldom the case when awakened from non-REM sleep.

Following the initial REM discoveries, sleep research greatly increased. One important discovery arising from this research was the high prevalence of sleep disorders, some of which now explain problems previously blamed on obscure physical or psychological disorders but which could not be effectively treated by medicine or psychiatry.

Combined, the EEG, EOG, and EMG produce a fascinating picture of sleep's structure. These monitoring devices transfer electronic stimulus to magnetic tapes, or on to paper via mechanical pens. The number of complete brain wave cycles per second are measured in "hertz" (Hz) by the EEG. The difference between the highest and lowest point of each wave (the peak and trough) is measured in" amplitude," (millionths of a volt, or microvolts-uV). As sleep approaches and deepens, hertz decrease and amplitude increases.

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