image007
One of the most spectacular observations during these time-isolation experiments in caves, laboratories, and other settings is the way that subjects’ sleep-wake cycles shift relative to the actual alternation of day and night in the outside world. But as soon as the experiments are over, the subjects take only a few days to resynchronize their cycles to these external time cues. This shift and the return to normal are shown in the diagram shown, where each line represents one day in a time-isolation experiment that lasted a month and a half. The solid part of each line represents the period when the subject was asleep, the dotted part represents the period when the subject was awake, and the triangle marks the time when the subject’s body temperature was lowest. (Image and description taken from www.thebrain.mcgill.ca)