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K complex

A sharp, negative EEG wave followed by a high-voltage slow wave, lasting at least 0.5 second. K complex waves are one of the characteristics of N2 (Stage 2) sleep.


A term describing individuals who are predisposed to wake early and to be at their best in the morning. Also termed “morning-type.” Contrasts with “owl” (see entry). Such owl and lark predispositions may have a genetic component.


A hormone that stimulates satiety, and thus decreases appetite. Reduced sleep duration may lead to a reduction in leptin, thereby stimulating appetite. See also ghrelin.

Maintenance of Wakefulness Test (MWT)

A sleep laboratory test that consists of several 40-minute periods of rest during which a patient must remain awake while sitting. This test is often used to determine a patient’s ability to stay awake, even in boring circumstances.

Memory acquisition: The initial step in forming a memory

The mechanism by which newly perceived information is received in the brain.

Memory consolidation: The second stage of memory

The neural processing that occurs after information is initially registered, which contributes to its permanent storage in memory.

Memory recall: The final stage of memory

The ability to access and utilize stored information.


A very brief period of sleep, lasting only a few seconds. Microsleeps occur most frequently when a very sleepy person is trying to stay awakeŃfor example, when driving while sleepy.


A central nervous system stimulant that promotes wakefulness. Modafinil is primarily used to treat the symptoms of excessive daytime sleepiness (EDS) in people with narcolepsy. See also excessive daytime sleepiness (EDS) and narcolepsy.

Motor neuron

A neuron that conveys signals from the central nervous system to a muscle.

Multiple Sleep Latency Test (MSLT)

A sleep laboratory test that consists of five 20-minute nap opportunities spread across the day. This test is used to measure a patient’s sleepiness. People with narcolepsy usually fall asleep in less than 8 minutes and have REM sleep in two or more of these naps.

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