“…Circadian rhythms and brain waves are in turn involved in sleep-wake processes, which are related to a neural circuitry consisting of the ascending wake-promoting pathway made of projections from various groups of cholinergic, noradrenergic, serotoninergic, dopaminergic, and histaminergic neurons located in the pedunculopontine and laterodorsal tegmental nucleus, locus coeruleus, dorsal and median raphe nucleus, and tuberomammillary nucleus, respectively. 10 , 11 However, every 24 h, the arousal system is inhibited during sleep by sleep-active Îł-aminobutyric acid (GABA)-ergic and galaninergic neurons of the ventrolateral preoptic nucleus (VLPO). 10 , 11 The reciprocal inhibitory exchange between the major ascending monoaminergic arousal groups and the sleep-inducing VLPO acts as a feedback loop; when monoamine nuclei discharge intensively during wakefulness, they inhibit the VLPO, and when VLPO fire rapidly during sleep, block the discharge of the monoamine cell groups, functioning like an electrical âon-offâ switch, enabling the body to maintain a stable state of wakefulness and sleep.…”