A Biphasic Daily Pattern of Slow Wave Activity During a Two Day 90 Minute Sleep-Wake Schedule

Abstract

Twenty-four hour sleep patterns were measured in six healthy male volunteers during a 90-minute short sleep-wake (SW 30:60) cycle protocol for 48 hours.   Sleep pressure estimates [amount of Slow Wave Sleep (SWS), SWA, and Rate of Synchronization (RoS: the rate of SWA build-up at the beginning of the NREM period)] were compared with the 24-hour patterns of body temperature (Tb₂₄) and sleep propensity. A moderate sleep debt was incurred over the 48 hour study as indicated by decreased levels of 24 hour sleep. On day 1, ultradian patterns of REM and SWS sleep were prominent; on day 2, more prominent were circadian patterns of REM sleep, SWS, Sleep Latency, TST and Tb₂₄. Also on Day 2, biphasic patterns of SWA and RoS were expressed, with peaks occurring during the falling and rising limbs of Tb₂₄. The biphasic peaks in SWA and RoS may be associated with phase-specific interactions of the circadian pacemaker with the sleep homeostat during conditions of moderate sleep pressure.  Further research is needed to identify specific biological factors that underlie the twelve hour pattern in SWA.