To assess the effects of gradual and mild sleep restriction on homeostatic regulation of sleep, electroencephalographic (EEG) delta-band power in the range of 1-4 Hz and sleep variables were analyzed simultaneously with sleep perception. The experiment consisted of three sessions; eight young volunteers were asked to (1) keep their normal sleep habits for 6 days (Baseline Night session); (2) delay their bed time by 20 min/night for 6 days (Delay Night session); and (3) advance their bed time by 20 min/night for 6 days (Recovery Night session), maintaining their normal rise time. The volunteers were monitored by sleep log and actigraphy. One night polysomnography in-lab was performed on the last day of each session.
Time in bed significantly differed among sessions, indicating a fairly high adherence to the experimental schedule. EEG delta-band power significantly increased, as well as slow wave sleep, during the first 1 hour after sleep onset of Delay Night compared to Baseline Night, which in turn showed a steep decline across sleep cycles. There was no difference either in total delta power or in sleep variables for the first 5 hours of sleep. Perception of sleep maintenance and initiation of sleep, assessed by OSA sleep questionnaire, seemed to slightly improve during Delay Night session. These results suggest that gradual and mild sleep restriction may lead to acceleration of build-up and dissipation of sleep pressure, based on sleep homeostasis.