Fig. 4. As a brief demonstration of the circadian rhythm, we left the lights on (A; male 029) or off (B; male 042) after completing an experiment. Under constant light or constant dark, EOD repolarization time (-P2) and amplitude (not shown) continue to oscillate on a shortened circadian rhythm, though the rise under free-running conditions is not as steep as occurs immediately after lights out in laboratory conditions. Vertical dashed lines indicate the previous times of lights on or off.