Wakefulness is a daily recurring
brain state and state of
consciousness in which an individual is conscious and engages in coherent
cognitive and behavioral responses to the external world.
Being awake is the opposite of being
asleep, in which most external inputs to the brain are excluded from neural processing.[1][2][3][4]
Effects upon the brain
The longer the brain has been awake, the greater the synchronous firing rates of
cerebral cortex neurons. After sustained periods of sleep, both the speed and synchronicity of the neurons firing are shown to decrease.[5]
Another effect of wakefulness is the reduction of
glycogen held in the
astrocytes, which supply energy to the neurons. Studies have shown that one of sleep's underlying functions is to replenish this glycogen energy source.[6]
Wakefulness is produced by a complex interaction between multiple neurotransmitter systems arising in the
brainstem and ascending through the
midbrain,
hypothalamus,
thalamus and
basal forebrain.[7] The posterior hypothalamus plays a key role in the maintenance of the cortical activation that underlies wakefulness. Several systems originating in this part of the brain control the shift from wakefulness into sleep and sleep into wakefulness.
Histamine neurons in the
tuberomammillary nucleus and nearby adjacent posterior hypothalamus project to the entire brain and are the most wake-selective system so far identified in the brain.[8] Another key system is that provided by the
orexins (also known as hypocretins) projecting neurons. These exist in areas adjacent to histamine neurons and like them project widely to most brain areas and associate with
arousal.[9] Orexin deficiency has been identified as responsible for
narcolepsy.[10]
Research suggests that orexin and histamine neurons play distinct, but complementary roles in controlling wakefulness with orexin being more involved with wakeful behavior and histamine with cognition and activation of cortical
EEG.[11]
It has been suggested the
fetus is not awake, with wakefulness occurring in the
newborn due to the stress of being
born and the associated activation of the
locus coeruleus.[12]