Wakefulness

Wakefulness is the state of being awake, marked by responsiveness to the environment and distinct from sleep. It varies in alertness and can be altered by brain activity, drugs, and illness.

Ascending reticular activating system: A network of brainstem pathways that activates the cerebral cortex and supports wakefulness. Its projections help maintain cortical activation during waking.
Sleep: A recurring, reversible state of reduced responsiveness and altered brain activity. Sleep is the principal physiological state contrasted with wakefulness.
Electroencephalography: A method that records electrical activity from the scalp using electrodes. EEG patterns help distinguish waking from sleep and altered states.
Vigilance: The ability to sustain attention and detect infrequent or unpredictable signals over time. Wakefulness enables vigilance, but does not guarantee it.
Orexin: A hypothalamic neuropeptide that promotes wakefulness and stabilizes sleep–wake transitions. Loss of orexin signaling can destabilize waking and cause narcolepsy.
Arousal: A state of physiological and neural activation that ranges from drowsiness to intense alertness. Arousal varies within wakefulness rather than defining it alone.
Multiple Sleep Latency Test: A daytime sleep study that measures how quickly a person falls asleep across scheduled nap opportunities. It quantifies difficulty sustaining wakefulness in disorders such as narcolepsy.
Reaction time: The interval between a stimulus and the initiation of a response. Declining alertness during prolonged waking can slow responses.
Locus coeruleus: A brainstem nucleus whose noradrenergic neurons influence alertness, attention, and stress responses. Its activity helps tune arousal during wakefulness.
Consciousness: The condition of having subjective experience or awareness. Wakefulness is one aspect of consciousness, not a complete account of it.

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