Before discussing alcohol's effects on sleep, it is helpful to summarize some basic features of normal sleep. A person goes through two alternating states of sleep, characterized in part by different types of brain electrical activity (i.e., brain waves). These states are called slow wave sleep (SWS), because in this type of sleep the brain waves are very slow, and rapid eye movement (REM) sleep, in which the eyes undergo rapid movements although the person remains asleep.

Most sleep is the deep, restful SWS. REM sleep occurs periodically, occupying about 25 percent of sleep time in the young adult. Episodes of REM normally recur about every 90 minutes and last 5 to 30 minutes. 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 (3). In addition, a transitional stage of light sleep occurs at intervals throughout the sleep period (4).

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. Some of these nerve cells produce serotonin, a chemical messenger associated with sleep onset (5) and with the regulation of SWS. Certain other nerve cells produce norepinephrine, which helps regulate REM sleep and facilitates arousal (6). The exact roles and interactions of these and other chemical messengers in orchestrating sleep patterns are not known (6). Significantly, however, alcohol consumption affects the function of these and other chemical messengers that appear to influence sleep.