ABSTRACTThis study was designed to determine the effects of presleep activity on a variety of physiological variables during 3½ hrs of subsequent sleep. Three presleep conditions were investigated for each of 15Ss:6 hrs of strenuous physical exercise, 6 hrs of concentrated studying, and 6 hrs of relaxation, i.e. watching TV, listening to records, and reading magazines. The following variables were recorded during a 3½ hr sleep period: EEG, EOG, body movements, heart rate, respiratory rate, peripheral pulse voltime, phasic vasoconstrictions, rectal temperature, and rapid variations in skin potential.None of the experimental presleep activities influenced the EEG cycle during the 3½ hrs of sleep. In particular, there were no significant differences in the following measurements as a result of presleep condition: amount of REMP time, time to first REMP, amount of delta sleep, time to first delta sleep, amount of stage 2 sleep, or number of sleep stage changes. These findings indicate a surprising stability of the sleep stage cyclevis a visthe markedly different evening activities.Physiological arousal after exercise decreased rapidly until it was no longer distinguishable from the base levels following studying or relaxation. A tendency to approach these base levels was observed even in heart rate, a variable which remained elevated after exercise throughout the 3½ hrs of sleep. For none of the physiological variables was the level of physiological arousal during sleep inversely related to the level of physiological arousal during wakefulness.Relating EEG sleep stages to the other variables of this study, it was observed that on nights when respiratory rate was high there was more delta sleep and less stage 2 sleep. Also, respiratory minima were most often found during stage 2 sleep immediately following a REMP, and respiratory maxima during NREM sleep were significantly associated with delta sleep. These results support Bülow's (1963) proposal that a close coupling exists between respiratory centers and those neural structures that regulate EEG aro