Sleep and wakefulness are endogenous, recurring, behavioral states that reflect coordinated changes in the dynamic functional organization of the brain and that optimize physiology, behavior, and health. Homeostatic and circadian processes regulate the propensity for wakefulness and sleep. Sleep:
- Is reversible, typically characterized by postural recumbence, behavioral quiescence, and reduced responsiveness;
- Has a complex architecture with predictable cycling of NREM/REM states or their developmental equivalents. NREM and REM sleep have distinct neural substrates (circuitry, transmitters, modulators) and EEG oscillatory properties
- Intensity and duration is affected by homeostatic regulation;
- Is affected by experiences during wakefulness;
- Is evident at cellular, circuit, and system levels;
- Has restorative and transformative effects that optimize neurobehavioral functions during wakefulness.