Awake (wakefulness): state, biology, rhythms and behaviour

Characteristics and biology

Wakefulness has characteristic behavioral and physiological signs: open eyes, purposeful movements, fast reaction times, and particular brain electrical patterns. On electroencephalography (EEG) wakeful activity tends to show low-amplitude, higher-frequency rhythms (beta) and, when relaxed with eyes closed, increased alpha activity. Wakefulness depends on a network of brain regions sometimes called the ascending arousal system or reticular activating system. Several neurotransmitters—acetylcholine, norepinephrine, histamine and orexin (hypocretin)—support cortical activation and sustained attention.

Daily rhythms and animal activity

The propensity to be awake is shaped by two interacting biological processes: a circadian rhythm that times sleep and wake across roughly 24 hours, and a homeostatic drive that increases sleep need the longer one stays awake. Different species and individuals follow different patterns. Many animals are awake during daylight and are described as diurnal, while others are awake at night and are nocturnal. Some species are crepuscular, most active at dawn and dusk. In general, animals spend several hours awake each day or night; for humans this morning awakening is often called waking up or getting out of bed (morning routines).

Common behaviours and examples

When awake an organism can perform a wide range of behaviours. Human wakeful activities include social interaction and speech, mobility and exercise, work and study, and ingesting food. Simple examples are speaking or gesturing to another person (communication) and taking meals or snacks (eating). In animals, wakeful periods are devoted to foraging, mating, territorial defence, care of offspring and navigation.

Transitions, disorders and variability

Transitions between sleep and wake are not instantaneous. On waking people often experience sleep inertia — impaired performance and grogginess that fades over minutes to an hour. Chronic problems include insomnia (difficulty maintaining wakeful alertness at desired times) and hypersomnia or narcolepsy (excessive daytime sleepiness and sudden sleep episodes). Individual differences, age and medical conditions alter typical patterns of wakefulness.

Importance and measurement

Wakefulness is central to cognition, safety and quality of life: attention, memory encoding, decision-making and motor control require appropriate arousal. Clinically and scientifically it is measured with EEG, behavioural vigilance tests and movement monitors (actigraphy). Understanding wakefulness also informs work schedules, transportation safety, and treatment of sleep disorders. For further general background about animals and humans in this context see animals and humans, and for daily timing issues see daily hours and cycles.