Sleep and sleepiness following a behaviourally ‘active’ day

During 4 day periods in which a total of nine subjects expected to spend each daytime under relatively stereotyped environmental conditions, a substitution was made for 1 day (experimental day) on a random basis. Here, subjects spent the time in a variety of novel, interesting and perceptually stimulating environments. Sleep EEG recordings were made each night following an adaptation night. Self-assessment sleepiness ratings were made night and morning. Following the experimental day subjects felt significantly more sleepy at bedtime, and sleep onset latency was significantly reduced. Although sleep length was unchanged, deep (slow wave) sleep, particularly stage 4 sleep, was increased significantly. There was some increase in sleep disturbance. REM sleep was unaffected. Subjects awoke feeling refreshed the next day. There was a small but significant carryover of a further SWS increase in the first part of the following night.