Slow wave activity and prior sleep/wakefulness on an irregular schedule

Eight subjects were exposed to a sleep schedule of 8, 4, 2, or 0 h of night sleep (awakening at 07 hours) followed by ad lib sleep from 1100 hours. Stepwise multiple regression analysis showed that SWA per cycle was closely related to the amount of prior waking, the amount of prior napping and the amount of prior sleep in the same sleep episode. The homeostatic 'factor S' of the three-process model of sleep regulation of Folkard and Åkerstedt predicted as much of the variance of SWA as did the three prior sleep/wake variables together. It was concluded that SWA is closely related to prior sleep/wake history and follows a course similar to that of recovery of alertness.