PhD Scientific Days 2023

Mental Health Sciences II.

Searching for Novel EEG Measures of Fundamental Sleep Regulatory Processes

Text of the abstract

Introduction
Sleep-wake history and time-of-day determine the fundamental features of sleep, being modelled in homeostatic and circadian processes, respectively. The individual differences within the latter can be described with the concept of chronotype.
Aims
Our goal is to provide reliable EEG indexes of these processes. We hypothesize that the slope of the NREM EEG spectrum (aperiodic component of EEG activity) is an indicator of sleep homeostasis, while the phase of the nadir of sleep spindle frequency is a possible index of chronotype.
Methods
Study 1: we analysed the first sleep cycles of 10 healthy young adults (20-26 years, 7 females) before and after 35 hours of wakefulness (challenging the sleep homeostat). The spectrum was parameterized using the FOOOF method. Study 2: we analysed 31 healthy young adults’ (17 female) questionnaire-based chronotype indexes (MCTQ), 5-day long actigraphy, one-night of sleep EEG, saliva melatonin, and sleep diaries. Phases of the nadirs of sleep spindle frequencies were estimated, and correlated with other chronotype variables.
Results
In study 1 we found that compared to baseline, the EEG spectrum of the first NREM period became significantly steeper (p<0.001) in recovery sleep, whereas the peak frequency of the sigma range increased at a trend level (p=0.07). In study 2, our preliminary results revealed a correlation of the time of slow spindle frequency nadir with relevant MCTQ measures (r=0.45; p=0.01), and actigraphy indexes (r=0.59; p<0.001). Furthermore, chronotype derived from actigraphy and phase of slow spindle nadir did not differ significantly (Ma=1.15, SD=0.05, Ms=1.14, SD=0.08, t(30)=0.76, p=0.456).
Conclusion
We can conclude that the steeper EEG spectrum in recovery sleep reflects increased homeostatic pressure induced by deprivation, while the tendency for an increased sigma peak frequency (in the first cycle of sleep) could reflect an advanced circadian phase due to earlier sleep timing. Moreover, study 2 suggest, that the time of spindle frequency minimum reflects the subjective and objective measures of chronotype.
Funding
SUPPORTED BY THE ÚNKP-22-3-II NEW NATIONAL EXCELLENCE PROGRAM OF THE MINISTRY FOR CULTURE AND INNOVATION FROM THE SOURCE OF THE NATIONAL RESEARCH, DEVELOPMENT AND INNOVATION FUND