Temperature, time-of-night of testing, and responsiveness to stimuli presented while sleeping

The present study examined how time-of-night of testing and body temperature related to responsiveness to stimuli presented in sleep. Nine males slept for two nonconsecutive nights in the sleep laboratory. On Night 1, tympanic temperature was assessed at 30-min intervals. On Night 2, responsiveness was assessed with an incremental series of tones (5dB steps) presented in sleep stages 2, 3/4, and REM throughout the night (0030-0800 h). Subjects were instructed and given practice prior to sleep to make a microswitch closure to the tones. Results showed a curvilinear pattern of responsiveness across the night in that the intensity of tones required for a response increased until about 0530 h, then decreased thereafter. This pattern of responsiveness was positively related to the circadian rhythm of body temperature. A close correspondence was also found between the temperature trough and the performance trough (both occurred at about 0530 h). A greater emphasis on circadian factors may help understand previously reported but contradictory findings. The present results also suggest that measures of responsiveness follow a circadian pattern regardless of the sleep/wake state.