FIGURE 1.

Core behavioral features of sleep

A: rapidly reversible quiescence can be demonstrated with a sufficiently strong stimulus, thus distinguishing sleep from seizure, coma, hibernation, and anesthesia. B: reduced arousal. A greater stimulus intensity is required to evoke a given behavioral response during sleep (red line) than during wakefulness (black line). C: the homeostatic nature of sleep is apparent from animals’ attempts to compensate for lost sleep. Black and red lines illustrate typical sleep cycles for control and sleep-deprived groups, respectively. Yellow bar indicates period of sleep deprivation. The next day, the sleep-deprived group sleeps more (i.e., rebounds) compared with the control.