The suprachiasmatic nucleus and sleep-wake regulation.

Human behavior is organized into 24-hour cycles that are typically composed of about 16 hours of wakefulness and about 8 hours of sleep. Sleep is an essential behavior and is critical for maintaining normal adaptive waking behavior. Both sleep and wake are initiated and maintained by separate and specific neural systems. The sleep-wake cycle is a function of 2 processes--a homeostatic drive for sleep that increases throughout the waking day and an opposing circadian influence that promotes wakefulness centered in the suprachiasmatic nucleus (SCN). A better understanding of the basis for sleep can help treatment and direct research about sleep.