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A phase response curve to single bright light pulses in human subjectsThe circadian pacemaker is differentially sensitive to the resetting effects of retinal light exposure, depending upon the circadian phase at which the light exposure occurs. Previously reported human phase response curves (PRCs) to single bright light exposures have employed small sample sizes, and were often based on relatively imprecise estimates of circadian phase and phase resetting. In the present study, 21 healthy, entrained subjects underwent pre- and post-stimulus constant routines (CRs) in dim light (approximately 2-7 lx) with maintained wakefulness in a semi-recumbent posture. The 6.7 h bright light exposure stimulus consisted of alternating 6 min fixed gaze (approximately 10 000 lx) and free gaze (approximately 5000-9000 lx) exposures. Light exposures were scheduled across the circadian cycle in different subjects so as to derive a PRC. Plasma melatonin was used to determine the phase of the onset, offset, and midpoint of the melatonin profiles during the CRs. Phase shifts were calculated as the difference in phase between the pre- and post-stimulus CRs. The resultant PRC of the midpoint of the melatonin rhythm revealed a characteristic type 1 PRC with a significant peak-to-trough amplitude of 5.02 h. Phase delays occurred when the light stimulus was centred prior to the critical phase at the core body temperature minimum, phase advances occurred when the light stimulus was centred after the critical phase, and no phase shift occurred at the critical phase. During the subjective day, no prolonged 'dead zone' of photic insensitivity was apparent. Phase shifts derived using the melatonin onsets showed larger magnitudes than those derived from the melatonin offsets. These data provide a comprehensive characterization of the human PRC under highly controlled laboratory conditions.
Document ID
20040087720
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Khalsa, Sat Bir S.
(Brigham and Women's Hospital, Harvard Medical School Boston, MA 02115, United States)
Jewett, Megan E.
Cajochen, Christian
Czeisler, Charles A.
Date Acquired
August 21, 2013
Publication Date
June 15, 2003
Publication Information
Publication: The Journal of physiology
Volume: 549
Issue: Pt 3
ISSN: 0022-3751
Subject Category
Life Sciences (General)
Funding Number(s)
CONTRACT_GRANT: F33-HL09588
CONTRACT_GRANT: R01-MH45130
CONTRACT_GRANT: M01-RR02635
Distribution Limits
Public
Copyright
Other
Keywords
Randomized Controlled Trial
NASA Discipline Regulatory Physiology
Clinical Trial
Non-NASA Center
NASA Program Biomedical Research and Countermeasures

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