Effects of self-awakening on sleep structure of a daytime short nap and on subsequent arousal levels.

To investigate the effects of self-awakening on sleep structure and daytime arousal after a short nap, a within-subjects comparison was made of participants in self-awakening and forced-awakening conditions. In the self-awakening condition. participants were instructed to wake up by themselves 15 min. after the experimenter turned the lights off. In the forced-awakening condition, the experimenter awakened them 20 min. after the lights were turned off. To control the maximum sleep time for the two conditions, we used different instructions in each condition. Participants were 10 healthy college students. Their physiological arousal and subjective sleepiness were evaluated using the P300 amplitude of the auditory event-related potential (ERP) and the visual analog scale previously described by Monk and Kathryn, et al. For evaluating sleep structure during the nap, Hori's 1994 hypnagogic EEG stages were used. P300 amplitude was significantly lower, and subjective sleepiness was significantly higher after forced-awakening than self-awakening, indicating that arousal was higher after self-awakening. The EEGs during napping in the forced-awakening condition indicated deeper sleep. Given this deeper sleep, severe sleep inertia occurred after the forced-awakening condition. In conclusion, it appeared a short nap with self-awakening was more effective in reducing a post-lunch dip than one with forced-awakening.