Sleep-wake cycles in Humans

Sleep-wake cycles in human are unique in several aspects. First, human sleep and wakefulness are mostly consolidated except for the infantile and senile periods. Second, the sleep-wake cycle is synchronized because of the circadian rhythms in plasma melatonin and deep body temperature. Third, the polysomnography-based structure as well as the length of sleep depends on the circadian phase. The sleep-wake cycle is entrained by nonphotic time cues independent of the circadian pacemaker. Some of these characteristics are easily understood by assuming that the specific oscillator in the circadian domain regulates sleep and wakefulness. The animal model for the human circadian system is advanced and the brain dopaminergic mechanism is strongly suggested to be site of the oscillator(s) regulating the sleep-wake cycle.