REM sleep is less restful than SWS and is usually associated with dreaming. Although its function is unknown, REM appears to be essential to health. In rats, deprivation of REM sleep can lead to death within a few weeks. In addition, a transitional stage of light sleep occurs at intervals throughout the sleep period. Sleep was formerly attributed to decreased activity of brain systems that maintain wakefulness.
More recent data indicate that sleep, like consciousness, is an active process.
Sleep is controlled largely by nerve centers in the lower brain stem, where the base of the brain joins the spinal cord. Certain other nerve cells produce norepinephrine, which helps regulate REM sleep and facilitates arousal. The exact roles and interactions of these and other chemical messengers in orchestrating sleep patterns are not known. Significantly, however, alcohol consumption affects the function of these and other chemical messengers that appear to influence sleep. Alcohol and Sleep in Those Without Alcoholism Alcohol consumed at bedtime, after an initial stimulating effect, may decrease the time required to fall asleep.