APA Dictionary of Psychology

an inpatient test performed in a sleep laboratory in which the individual is monitored during a series of five 20-minute nap periods scheduled 2 hours apart. The object is to assess daytime sleep tendency by measuring the number of minutes it takes the individual to fall asleep. Electrodes are used to measure brain waves, eye movements, heartbeat, and muscle tone. The test is used in the diagnosis of primary hypersomnia and narcolepsy.