A social conflict increases EEG slow-wave activity during subsequent sleep

Electroencephalogram (EEG) slow-wave activity (SWA) during non-rapid eye mo vement (NREM) sleep is widely viewed as an indicator of sleep debt and slee p intensity. In a previous study, we reported a strong increase in SWA duri ng NREM sleep after a social conflict in rats. To test whether this increas e in SWA reflects normal physiological sleep or an unrelated by-product of the stress, we now measured the effect of a conflict in combination with ex tended sleep deprivation by means of gentle handling. We anticipated that i f the social defeat-induced SWA reflects a true sleep debt, the drive for i t would persist during the extended wakefulness. Male rats were subjected t o a l-h social conflict followed by 5 h of sleep deprivation by gentle hand ling or to 6 h gentle handling alone. The manipulations took place during t he second half of the dark phase and recovery sleep was recorded during the subsequent light phase. Neither of thr two procedures caused a significant change in the total duration of NREM or REM sleep thereafter. Yet, both mo des of sleep deprivation induced a strong increase in SWA during NREM sleep . This SWA was significantly higher for 6 h after sleep deprivation consist ing of a social conflict followed by gentle handling, as compared to sleep deprivation by handling alone. Thus, the SWA increasing effect of the confl ict persisted during the extended wakefulness. The data confirm that social defeat stress accelerates the build up of sleep debt and support the notio n that sleep debt and subsequent NREM sleep intensity not only depend on th e duration of prior wakefulness but also on what animals experience during that waking. (C) 2001 Elsevier Science Inc. All rights reserved.