Effective resetting of the internal circadian clock is necessary for circadian adaptation to jet lag and for the treatment of circadian sleep disorders. While it is generally recognized that photic and non-photic stimuli can phase shift the internal circadian timekeeping system, little is known about how photic and non-photic time cues are integrated to produce photic phase shifts of the human circadian clock. Results from studies predominantly conducted in non-humans indicate that photic and non-photic information is integrated by the circadian time keeping system. We hypothesize that photic and non-photic information is also integrated by the circadian time keeping system in humans. If the combination of photic and non-photic time cues enhances phase shifts in humans, such a finding would have important implications for the treatment of circadian-related sleep disorders and for rapid adaptation to jet lag. We propose to evaluate phase delays and phase advances of the human circadian clock induced by the combination of bright light exposure with non-photic cues. The current grant proposal is to improve our understanding of the mechanisms through which various stimuli such as light or endogenous factors entrain sleep and circadian rhythms. The research is novel in that it proposes to conduct a series of studies designed to systematically examine the ability of photic and non-photic information to be integrated by the human circadian clock and thus result in enhanced phase shifts of the human circadian timing system. We anticipate that the results of the proposed study may have significant implications for developing new treatments for jet lag and for sleep disorders that cause patients to go to bed much later or earlier than desired. The proposed treatments may also have implications for improving sleep in environments such as space flight.
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