48
Brain Facts
of norepinephrine within the RAS, which generates stimulating impulses that are fed into the cerebral cortex. However, not everyone remembers his or her dreams the next morning. Why sleep is necessary is not completely understood. Apparently, only higher vertebrates with fairly well-developed cerebral cortices have complex sleep patterns divided into different stages. When a person stays awake for unusually long periods, fatigue and irritability result, and even routine tasks cannot be performed well. It is thought that perhaps certain waste products accumulate within the nervous system, and sleep gives the nervous system an opportunity to dispose of them. Not only is non-REM sleep required, but REM sleep is apparently also essential. In sleep deprivation experiments performed with human volunteers, lack of REM sleep makes subjects anxious and irritable. After such experiments, when subjects are permitted to sleep normally again, they go through a period when they spend more time than usual in the REM stage. After recovery, there is no apparent long-lasting damage. Many types of drugs alter sleep patterns and affect the amount of REM sleep. For example, sleeping pills may increase the total sleeping time but decrease the time spent in REM sleep. When a person stops taking such a drug, several weeks may be required before normal sleep patterns are reestablished. Age and Sleep The percentage of REM sleep is highest during infancy and early childhood, drops off during adolescence and young adulthood, and decreases further in older age. Of course, infants require the greatest amount of sleep. As parents know, total sleep time typically becomes shorter during childhood and may become longer again in adolescence. The time dimensions of sleep change again as one ages: Older people get less total sleep than younger