Circadian phase resetting in response to light-dark and dark-light transitions (original) (raw)
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Circadian phase shifting: Relationships between photic and nonphotic phase–response curves
Physiology & Behavior, 2001
A variety of photic and nonphotic stimuli can phase-shift the mammalian circadian pacemaker. It has been suggested that the phase ± response curves (PRCs) characterizing these diverse stimuli may comprise two major PRC families, one typified by the photic PRC describing the response to brief light pulses, and the other typified by the nonphotic PRC describing the response to stimuli evoking behavioral arousal and/or locomotor activity. Additionally, the mammalian circadian pacemaker can be phase-shifted by dark pulses presented on a constant-light (LL) background. While dark pulse-induced phase shifting was interpreted originally as a mirror-image photic effect, other observations suggest that the dark pulse PRC may instead belong to the family of nonphotic, activity-dependent PRCs. In a recent study, we reexamined the phase-shifting effects of dark pulses in the Syrian hamster, and concluded that the dark pulse PRC reflects both nonphotic and photic mirror-image mechanisms. In the current report, we reanalyze previously published hamster PRC data using polynomial curve-fitting procedures. The results of these analyses reveal that (a) the photic and nonphotic PRCs have identical shape but opposite phasing, and (b) the dark pulse PRC can be modeled by simple summation of nonphotic and photic mirror-image PRCs. This model predicts accurately the shape of the dark pulse PRC, particularly the extension of the phase-advance region into the subjective night. D
American Journal of Physiology-Regulatory, Integrative and Comparative Physiology, 1997
Fifty-six resetting trials were conducted across the subjective day in 43 young men using a three-cycle bright-light (∼10,000 lx) stimulus against a background of very dim light (10–15 lx). The phase-response curve (PRC) to these trials was assessed for the presence of a “dead zone” of photic insensitivity and was compared with another three-cycle PRC that had used a background of ∼150 lx. To assess possible transients after the light stimulus, the trials were divided into 43 steady-state trials, which occurred after several baseline days, and 13 consecutive trials, which occurred immediately after a previous resetting trial. We found that 1) bright light induces phase shifts throughout subjective day with no apparent dead zone; 2) there is no evidence of transients in constant routine assessments of the fitted temperature minimum 1–2 days after completion of the resetting stimulus; and 3) the timing of background room light modulates the resetting response to bright light. These da...
Journal of Biological Rhythms, 2001
The suprachiasmatic nuclei of the hypothalamus contain the major circadian pacemaker in mammals, driving circadian rhythms in behavioral and physiological functions. This circadian pacemaker's responsiveness to light allows synchronization to the light-dark cycle. Phase shifting by light often involves several transient cycles in which the behavioral activity rhythm gradually shifts to its steady-state position. In this article, the authors investigate in Syrian hamsters whether a phase-advancing light pulse results in immediate shifts of the PRC at the next circadian cycle. In a first series of experiments, the authors aimed a light pulse at CT 19 to induce a phase advance. It appeared that the steady-state phase advances were highly correlated with activity onset in the first and second transient cycle. This enabled them to make a reliable estimate of the steady-state phase shift induced by a phase-advancing light pulse on the basis of activity onset in the first transient cyc...
Journal of Biological Rhythms, 2006
In nature, virtually all circadian rhythms assume the 24.0-h period of the solar day-night cycle. This is due to the entrainment of the endogenous oscillators to the external light-dark cycle, the dominant zeitgeber for the majority of organisms. The process of entrainment is based on differential phase and period responses of the circadian systems to light depending on the phase at which the stimulus is applied. The
Phase-dependent shift of free-running human circadian rhythms in response to a single bright pulse
Experientia, 1987
Responsiveness of free-running human circadian rhythms to a single pulse of bright light was examined in a temporal isolation unit. Bright light (5000 Ix) of either 3 or 6 h duration, applied during the early subjective day, produced phase-advance shifts in both the sleep-wake cycle and the rhythm of rectal temperature; the light pulse had essentially no effect on the phase of the circadian rhythms, when it was introduced during the late subjective day or the early subjective night. The results indicate that bright light can reset the human circadian pacemaker.
Human responses to bright light of different durations
The Journal of Physiology, 2012
• Light is the strongest time cue for entrainment and phase resetting of the circadian clock. • In humans, exposure to long-duration light (6.5 h) in the late evening/early night causes phase delays, suppresses melatonin and increases alertness. • Here we studied the effects of different durations of exposure to a single high-intensity (∼10,000 lux) light pulse (0.2 h, 1 h, 2.5 h and 4.0 h) on phase shifting, suppression of melatonin and self-reported sleepiness in young men and women. • Phase-resetting and melatonin-suppression responses were dose dependent and non-linear;