Neurobiological aspects of sleep physiology.

Sleep is characterized by changes in neural firing and chemistry compared with wakefulness. Many neurologic diseases affect pathways that regulate control of sleep state and some primary sleep disorders have abnormalities of this circuitry. Nonrapid eye movement (NREM) and rapid eye movement (REM) sleep alternate in an approximately 90-minute cycle. Recent findings have expanded understanding of the control of sleep state, and will facilitate development of novel therapeutics to assist patients with a variety of disorders of sleep and wakefulness. Treatment of sleep and wake disorders can assist patients with a variety of neurologic problems.