PhD Scientific Days 2024

Mental Health Sciences II.

Does the largest increase in REM/NREM ratio indicate circadian phase?

Text of the abstract

The circadian modulation of rapid-eye-movement (REM) sleep was proven several times. In the present study our aim was to assess the intraindividual consistency in the timing of the largest REM/NREM ratio increase and in the amount of accumulated REM sleep prior to this time. In addition, we aimed to test the interindividual differences in these putative phase indicators in terms of age, and their correlation with core body temperature/actigraphy derived chronotype measures.
Testing was performed by analysing the sleep records of 19 helathy adults (dataset 1) from a 35-hour long sleep deprivation protocol (baseline and recovery sleep), the registrations derived from 11 helathy adults’ sleep aligned with former core body temperature (CBT) measurements (dataset 2), as well as the Budapest-Munich database of sleep records (dataset 3: N = 251 healthy subjects). In dataset 1 the bed times were freely chosen by the participants at baseline sleep and the use of an alarm clock was prohibited. In dataset 2, subjects had to follow a regular sleep schedule for 1 week. CBT was measured in the first 48 hours, while the EEG recording started in the 6th evening of the week. Actigraphy was measured for 5 days in the first, and for 7 days in the second dataset. In dataset 3, participants slept in the lab (N=208) or in their homes (N=43).
Results indicate none of the chronotype-measures (MCTQ, actigraphy) correlate with the timing of the largest REM/NREM ratio increase in the sleep deprivation study and only the actigraphy-derived least-active 5 hours (L5) measure correlates strongly (r=0.6, p=0.02) with this putative phase indicator (dataset 2). Both the timing of the “jump” in R/N ratio and the prior REM accumulation differ significantly between baseline and recovery nights (dataset 1). However, prior REM accumulation correlates negatively with L5 and with the actigraphy derived chronotype measure (MSFsc) in baseline sleep. There is a significant difference in the timing of the jump (earlier for children and older adults then for teenagers and young adults; F=3.6 p=0.01) and also in the accumulation of REM (decreasing with age; F=6.3, p<0.001) between age groups.
Although two of the analysed datasets are small, these results are raising question on the stability of REM-sleep as a circadian phase-indicator, perhaps indicating a homeostatic function as well.