Sleep

Sleep is a recurring, reversible biological state marked by reduced responsiveness and characteristic brain and body activity. It supports functions including restoration, memory, and emotional regulation.

Non-rapid eye movement sleep: Sleep stages characterized by reduced eye movement, progressing from light sleep to deep slow-wave sleep. It supplies most deep slow-wave sleep, when arousal thresholds are highest.
Sleep spindles: Brief bursts of rhythmic brain activity characteristic of stage N2 non-REM sleep. They are a defining EEG feature of one major sleep stage.
Memory consolidation: The stabilization and reorganization of memories after initial learning. Sleep can support the consolidation of different kinds of newly learned information.
Insomnia: A disorder involving persistent difficulty falling asleep, staying asleep, or obtaining restorative sleep despite adequate opportunity. It is a common disorder defined by problems with sleep rather than its absence.
Rapid eye movement sleep: A sleep stage marked by rapid eye movements, vivid dreaming, and muscle atonia. Its distinctive brain activity and muscle paralysis contrast with non-REM sleep.
Slow-wave sleep: Deep non-REM sleep marked by large, slow brain waves. It is the deepest stage in the usual progression of non-REM sleep.
Emotional regulation: Processes that influence the intensity, duration, and expression of emotional responses. Sleep loss can impair emotional control and heighten reactivity.
Narcolepsy: A chronic neurological disorder involving excessive daytime sleepiness and unstable boundaries between sleep and wakefulness. It disrupts the normal separation and timing of sleep and wake.
Sleep architecture: The pattern and timing of sleep stages across a sleep period. It describes how non-REM and REM stages recur through the night.
Electroencephalography: A method for recording electrical activity from the brain using scalp electrodes. It reveals the changing brain-wave patterns used to classify sleep stages.

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