To Sleep, Perchance to Dream
Sleep is vital to health and well-being. Without it people behave oddly and have strange experiences. Studies have found that sleep deprivation for 100 hours or more leads to hallucinations, paranoia, and bizarre behavior. Without sleep, cognitive and motor functioning deteriorate for simple tasks, yet tasks demanding high concentration and skill can be performed with great dexterity. The odd effects of sleep deprivation are completely eliminated once a person is allowed a period of recovery sleep. Physiological recordings indicate that when people remain awake for over 200 hours they frequently experience periods of „microsleep” lasting two to three seconds. It appears that the body refuses to be entirely deprived of sleep for extended periods.
To study sleep, researchers bring people into the laboratory and record their activities as they sleep. Three types of recording devices are used simultaneously, the electroencephalograph (EEG), which records electrical activity in the brain, the electro-oculograph, which records the movement of the eyes, and the electromyograph(EMG), which measures muscle tension and activity.
One of the most important discoveries of sleep research is that a person’s eyes move rapidly during certain periods of the night. This phenomenon, termed rapid eye movement (REM), occurs during approximately 25 percent of the time a person is asleep. The rest of the time, eye movements are either slow and regular or nonexistent. The period of rapid eye movement is a distinct stage in the normal sleep cycle. Research on eye movement and brain activity has helped describe five stages that occur during the normal sleep cycle.
Stages 1 through 4 are generally referred to as non-REM (NREM) to distinguish them from the unique activity of REM sleep. As people cycle through the five stages of sleep several times over the course of a night, they will typically experience four to six periods of REM sleep. REM sleep is often called „paradoxical sleep” because it resembles both deep sleep and wakefulness. Although there are small movements and muscle twitches during REM, the body is immobilized-essentially paralyzed. At the same time, the eyes are moving back and forth at a high rate; blood flow to the brain increases; and the EEG shows brain wave activity that is almost identical to that of a waking and alert person. Eighty percent of the time that subjects are awakened from REM sleep and asked to report their experiences, they claim to have been dreaming.
When we are deprived of enough sleep or if the normal sleep cycle is disrupted, we suffer. In some cases, sleep disorders occur independent of other psychological or physical disorders; in other cases, the sleep disorders occur at the same time with mental or physical disorders, either as a result of the disorder itself or as a side effect of drugs used to treat the disorder.
Periodically during REM sleep, most people experience nightmares, or distressful, frightening dreams that awaken them, but their nightmares are usually infrequent and short-lived and do not affect normal functioning. Sometimes, chronic nightmares persist and cause great distress; such cases should be treated with psychotherapy or mild drug therapy. These nightmares often increase when the people are under stress. In over half of the cases, the problem begins before age 10. Another kind of nightmare is called night terror disorder, in which a person might awaken suddenly during the first hour of NREM sleep screaming out in extreme fear and agitation. He or she is in a state of panic, is often incoherent, and has a rapid heartbeat. Generally the sufferer does not remember the episode in the morning. Night terrors most often appear in young children: approximately 1 to 4 percent experience them at some time.
People with a sleepwalking disorder repeatedly leave their beds and walk around, without being conscious of the episode or remembering it later. The episodes occur when the person is in the stages of deep sleep and generally consist of sitting up, getting out of bed, and walking around, apparently with a specific purpose in mind. People who are awakened while sleepwalking are confused for several moments. If allowed to continue sleepwalking, they eventually return to bed, and generally do not recall the episode in the morning. Most people who sleepwalk manage to avoid obstacles, climb stairs, and perform complex activities, always in a seemingly emotionless and unresponsive state. Accidents do occur, however: tripping, bumping into objects, and even falling out of windows have all been reported. Approximately 1 to 5 percent of all children have this disorder at some time. As many as 15 percent of children have isolated episodes. The causes of sleepwalking are unknown, and it generally disappears by the age of 20.
Sleep and sleep disorders have become popular topics in the last decade, and sleep research laboratories are now found in many major cities. Because sleep is such a crucial component of existence, it is important to understand its underlying mechanisms. The results of sleep studies have implications not only for the treatment of sleep disorders and related psychological problems but for every human activity and endeavor.