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Phase-shifting human circadian rhythms: influence of sleep timing, social contact and light exposure1. Both the timing of behavioural events (activity, sleep and social interactions) and the environmental light-dark cycle have been reported to contribute to entrainment of human circadian rhythms to the 24 h day. Yet, the relative contribution of those putative behavioural synchronizers to that of light exposure remains unclear. 2. To investigate this, we inverted the schedule of rest, sedentary activity and social contact of thirty-two young men either with or without exposure to bright light. 3. On this inverted schedule, the endogenous component of the core temperature rhythm of subjects who were exposed to bright light showed a significant phase shift, demonstrating that they were adapting to the new schedule. In contrast, the core temperature rhythm of subjects who were not exposed to bright light moved on average 0.2 h later per day and after 10 days had not significantly adapted to the new schedule. 4. The direction of phase shift in the groups exposed to bright light was dependent on the time of bright light exposure, while control subjects drifted to a later hour regardless of the timing of their schedule of sleep timing, social contact and meals. 5. These results support the concept that the light-dark cycle is the most important synchronizer of the human circadian system. They suggest that inversion of the sleep-wake, rest-activity and social contact cycles provides relatively minimal drive for resetting the human circadian pacemaker. 6. These data indicate that interventions designed to phase shift human circadian rhythms for adjustment to time zone changes or altered work schedules should focus on properly timed light exposure.
Document ID
20040173163
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Duffy, J. F.
(Brigham and Women's Hospital, Harvard Medical School Boston, MA 02115, United States)
Kronauer, R. E.
Czeisler, C. A.
Date Acquired
August 22, 2013
Publication Date
August 15, 1996
Publication Information
Publication: The Journal of physiology
Volume: 495 ( Pt 1)
ISSN: 0022-3751
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: R01 AG06072
CONTRACT_GRANT: P01 AG09975
CONTRACT_GRANT: R01 MH45130
Distribution Limits
Public
Copyright
Other
Keywords
Non-NASA Center
NASA Discipline Regulatory Physiology

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