The role of ultradian rhythms in post-deprivationrebounds and diurnal rhythms of sleep and wakefulness in rats

The temporal organization of ultradian rhythms in sleep and wakefulness during post-sleep deprivation (TSD) rebound were investigated in 15 rats under contant bright light (LL). Following baseline recordings, rats were subjected to TSD using gentle manual stimulation. Post-TSD rebounds in cumulative wakefulness (WAKE), rapid eye movement sleep (REM) and non-REM sleep (NREM) were analyzed in WAKE-dominant ({upsilon}w) and sleep-dominant ({upsilon}s) ultradian phases. Rebounds in WAKE and NREM were present only when data were analyzed on a full ultradian cycle basis, and were absent in {upsilon}s and {upsilon}w phases alone. These rebounds were approximately 50% complete and not proportional to TSD excess/deficit. Rebounds in REM were present in full ultradian cycles and partially expressed in {upsilon}s but absent in {upsilon}w. REM rebounds fully compensated for REM deficit. Rebounds were mediated mainly by a reduction in the duration of the {upsilon}w ultradian phase, and by decreased probability of arousal in the {upsilon}s ultradian phase. These mechanisms were also found to partially mediate diurnal rhythms in 10 rats under a 12:12 h LD cycle. This study implicates an ultradian timing mechanism in the control of post-TSD rebounds and suggests that rebounds in all three states are mainly mediated by post-TSD adjustments in WAKE-promoting mechanisms. Ultradian rhythms should be taken into account to avoid errors in data analysis. HighlightsO_LISleep-wake state exhibits circadian rhythms and ultradian rhythms. C_LIO_LIThese rhythms interact with rebounds after sleep deprivation. C_LIO_LICircadian amplitude and sleep rebound are partially mediated by ultradian timing. C_LIO_LIArousal-related processes control these sleep-wake patterns in both states. C_LIO_LIMeasuring ultradian rhythms is necessary for accurate analysis of data. C_LI