TAU-CHANGES AFTER SINGLE NONPHOTIC EVENTS

Changes in the free-running period of the circadian rhythms of hamsters occur after single nonphotic events such as a 3-h pulse of running induced by being put in a novel wheel. These changes are mostly in the direction of longer periods, and can exceed 0.2 h; the magnitude of the effect depends on the circadian phase of the pulse. The phase response curves for period changes do not match up with those for phase shifts of the rhythms. Data on free-running rhythms after anisomycin injections and after novelty-induced wheel running in tau mutant hamsters support the view that period changes and phase shifts can occur independently of one another.