[Daily phase adjustment of human sleep-wake cycle].

In humans, studies using temporal isolation unit have indicated that (1) bright light is a dominant zeitgeber in human circadian systems and (2) period of endogenous circadian rhythms is longer than 24 h. The human circadian systems have at least two unique features. First is an internal desynchronization in which period of core body temperature rhythm and sleep-wake cycle free-run with different periods. Internal desynchronization indicates that the human circadian system consists of two different oscillators. One has a circadian period of about 25 h and drives the rhythms in rectal temperature and melatonin, and the other has a period longer than 30 h and drives the sleep-wake cycle. Second feature is non-photic entrainment of sleep-wake cycle to a strict social schedule (so called partial entrainment). In this review, we summarize and update the two oscillator model based on recent evidence obtained by sleep-wake schedule and physical exercise experiments under temporal isolation facility.