waking

Waking is the state of consciousness in which a person can perceive the environment, think, and act, distinct from sleep. It typically occurs after a sleep period and is part of the sleep–wake cycle.

Arousal and wakefulness are regulated by the ascending arousal system, including the brainstem reticular activating system, the thalamus, cortex, and several neuromodulatory networks (norepinephrine from locus coeruleus, serotonin from raphe, acetylcholine from basal forebrain, histamine from tuberomammillary nucleus, orexin from hypothalamus). Activation raises cortical activity, changing EEG patterns from sleep to wake (from slow-wave or REM patterns to beta activity). Circadian and homeostatic processes modulate waking: light promotes wakefulness by suppressing melatonin and activating the hypothalamic-pituitary-adrenal axis; sleep pressure dissipates during the night.

Transition and routine: Waking involves moving from sleep stages, often with a brief transition called sleep inertia, during which cognitive performance may be impaired. In healthy adults, morning waking becomes more consistent with circadian cues; in infants and older adults, patterns vary.

Disturbances and management: Chronic difficulty waking or maintaining alertness can reflect insomnia, hypersomnia, circadian rhythm disorders, sleep apnea, or other medical or psychiatric conditions. Caffeine, light exposure, and medications or therapies promoting wakefulness may be used to manage excessive sleepiness.