Good sleep — its timing and physiological sleep characteristics

The present study used short sleep episodes to explore the relation between subjective sleep quality, timing and physiological content of sleep. Eight subjects participated in 18 4-h sleep episodes to provide 4, 8, and 12 h of prior time awake before bedtimes at six different times of day in a sleep laboratory insulated from environmental disturbances. The results were analysed by ANOVAs and multiple regression techniques. Subjective sleep quality, calmness of sleep, ease of falling asleep, ability to 'sleep through', number of awakenings, and sleep latency showed a significant pattern of 'better' sleep with increasing prior time awake and with closeness to the circadian minimum (nadir) of rectal temperature (morning hours). 'Ease of awakening' in contrast, 'decreased' with increasing time awake and with closeness to the nadir/ morning hours. Multiple regression analysis showed that subjective sleep quality was predicted by subjective calmness of sleep and ease of falling asleep, among the subjective measures, and by total sleep time (TST) and slow-wave sleep (SWS - stages 3+4) among the physiological sleep measures. The subjective ease of awakening was predicted by slow-wave sleep (negatively) and the circadian maximum of rectal temperature. The results indicate that the duration of wakefulness prior to sleep and the timing of sleep determine its physiological expression, which in turn determines its subjective impression.