HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Duffy, J F Articles by Czeisler, C A Search for Related Content PubMed PubMed Citation Articles by Duffy, J F Articles by Czeisler, C A

Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.

1. 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.

This article has been cited by other articles:

				G. Vandewalle, S. Gais, M. Schabus, E. Balteau, J. Carrier, A. Darsaud, V. Sterpenich, G. Albouy, D. J. Dijk, and P. Maquet Wavelength-Dependent Modulation of Brain Responses to a Working Memory Task by Daytime Light Exposure Cereb Cortex, December 1, 2007; 17(12): 2788 - 2795. [Abstract] [Full Text] [PDF]