Double-pulse experiments with nonphotic and photic phase-shifting stimuli.

Three-hour pulses of novelty-induced wheel running in the early to middle subjective day of golden hamsters produced phase advances of 2-3 hr. This phase shifting could be almost totally abolished by a light pulse following within 3 hr of the exercise pulse. When light pulses occurred about 8 hr after the exercise pulses, the phase-advancing effects of the latter were enhanced. Consideration of the amplitude of the phase response curve (PRC) for light pulses alone, in the test paradigms used here, showed that nonphotic and photic phase shifts did not combine additively. Antagonistic and synergistic interactions between photic and nonphotic shifts may have to be taken into account if it transpires that exercise in people can be used to assist adjustment to new schedules after crossing time zones, or in shiftwork.