Links between the number of sleep ultradian cycles and REMS duration: Confirmation in rats

Sleep ultradian cycling: Statistical distribution and links with other sleep variables, depression, insomnia and sleepiness-A retrospective study on 2,312 polysomnograms

The number of alternations between Non-Rapid Eye Movement (NREM) sleep and Rapid Eye Movement (REM) sleep in humans is usually considered to consist of 4-5 cycles of about 90 minutes duration per night. Previous studies by our group showed a normal distribution on 26 healthy human subjects. The present study retrospectively analyzes the polysomnograms of 2,312 unmedicated patients who were admitted for medical and/or psychiatric reasons in the Erasme University Hospital between 2003 and 2014. The normal distribution of the Number of Cycles and Mean Cycle Duration was confirmed. Q-Q plots were very close to linearity. This distribution allows the use of these variables in parametric comparisons. The Number of Cycles per night and the Mean Cycle Duration showed predominant links with REM sleep-related variables, such as the REM Latency, REM sleep duration, the REM/NREM sleep ratio. None of these variables was associated with the diagnosis of Major Depressive Disorder, nor the intensity of Depression as measured by the Beck Depression Inventory (short version). On the other hand, the diagnosis of Major Depressive Disorder was significantly associated with the Insomnia Severity Index and correlated with the intensity of depressive symptoms (Beck Depression Inventory).

Absence of systematic relationships between REMS duration episodes and spectral power Delta and Ultra-Slow bands in contiguous NREMS episodes in healthy humans

Previous studies in animals and humans have reported correlations between the durations of rapid eye movement sleep (REMS) episodes and immediately preceding or subsequent non-REMS (NREMS) episodes. The relationship between these two types of sleep is a crucial component in understanding the regulation and neurophysiology of ultradian alternations that occur during sleep. Although the present study replicated previous studies, we also measured NREMS in terms of spectral power Delta and Ultra-Slow bands in addition to duration in examining correlations. The spectral power Delta band, also known as slow-wave activity, measures sleep quantity and is believed to reflect sleep physiology better than mere episode durations. The Ultra-Slow spectral power band was analyzed in parallel. Healthy human participants of both sexes ( n = 26, age range 15–45 yr, n = 12 female) were carefully selected to participate in two consecutive series of home polysomnograms performed after 2 nights of habituation to the equipment. In the analyses, REMS episode durations (minutes) were compared with immediately preceding and immediately subsequent NREMS episodes (Delta and Ultra-Slow power) in each sleep cycle. REMS episode duration was more strongly correlated with preceding NREMS episodes than with subsequent NREMS episodes. However, in most cases, no correlations were observed in either direction. One ultradian sleep regulation hypothesis, which is based on stronger correlations between REMS and subsequent NREMS episode durations, holds that the main purpose of REMS is to reactivate NREMS during each sleep cycle. The present results do not support that hypothesis.