title: The timing of the human circadian clock is accurately represented by the core body temperature rhythm following phase shifts to a three-cycle light stimulus near the critical zone.
abstract: A double-stimulus experiment was conducted to evaluate the phase of the underlying circadian clock following light-induced phase shifts of the human circadian system. Circadian phase was assayed by constant routine from the rhythm in core body temperature before and after a three-cycle bright-light stimulus applied near the estimated minimum of the core body temperature rhythm. An identical, consecutive three-cycle light stimulus was then applied, and phase was reassessed. Phase shifts to these consecutive stimuli were no different from those obtained in a previous study following light stimuli applied under steady-state conditions over a range of circadian phases similar to those at which the consecutive stimuli were applied. These data suggest that circadian phase shifts of the core body temperature rhythm in response to a three-cycle stimulus occur within 24 h following the end of the 3-day light stimulus and that this poststimulus temperature rhythm accurately reflects the timing of the underlying circadian clock.
authors: Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA.
authors: Khalsa SBS
authors: M E
authors: ME
authors: Jewett
authors: J F
authors: JF
authors: Duffy
authors: C A
authors: CA
authors: Czeisler
mesh_terms: D000328:Adult; D001683:Biological Clocks / Q000502:physiology*; D001831:Body Temperature / Q000502:physiology*; D002940:Circadian Rhythm / Q000502:physiology*; D003624:Darkness; D006801:Humans; D008027:Light; D008029:Lighting; D008297:Male; D017440:Photoperiod; D012016:Reference Values; D015203:Reproducibility of Results