Overnight dynamics in scale-free and oscillatory spectral parameters of NREM sleep EEG

EEG. Scientific Reports 12: 18409 (2022)

DOI: 10.1038/s41598-022-23033-y

Csenge G. Horváth1, Orsolya Szalárdy1,2, Péter P. Ujma1, Péter Simor3,4, Ferenc Gombos5,6, Ilona Kovács6, Martin Dresler7, Róbert Bódizs1

1Institute of Behavioural Sciences, Semmelweis University, Budapest, Hungary

2Institute of Cognitive Neuroscience and Psychology, Research Centre for Natural Sciences, Budapest, Hungary

3Institute of Psychology, ELTE, Eötvös Loránd University, Budapest, Hungary

4UR2NF, Neuropsychology and Functional Neuroimaging Research Unit at CRCN-Center for Research in Cognition and Neurosciences and UNI-ULB Neurosciences Institute, Université Libre de Bruxelles (ULB), Brussels, Belgium

5Laboratory for Psychological Research, Pázmány Péter Catholic University, Budapest, Hungary

6ELRN-ELTE-PPKE Adolescent Development Research Group, Faculty of Education and Psychology, Eötvös Loránd University, Budapest, Hungary

7Donders Institute for Brain, Cognition and Behaviour, Radboud University Medical Center, Nijmegen, The Netherlands


Unfolding the overnight dynamics in human sleep features plays a pivotal role in understanding sleep regulation. Studies revealed the complex reorganization of the frequency composition of sleep electroencephalogram (EEG) during the course of sleep, however the scale-free and the oscillatory measures remained undistinguished and improperly characterized before. By focusing on the first four non-rapid eye movement (NREM) periods of night sleep records of 251 healthy human subjects (4–69 years), here we reveal the flattening of spectral slopes and decrease in several measures of the spectral intercepts during consecutive sleep cycles. Slopes and intercepts are significant predictors of slow wave activity (SWA), the gold standard measure of sleep intensity. The overnight increase in spectral peak sizes (amplitudes relative to scale-free spectra) in the broad sigma range is paralleled by a U-shaped time course of peak frequencies in frontopolar regions. Although, the set of spectral indices analyzed herein reproduce known age- and sex-effects, the interindividual variability in spectral slope steepness is lower as compared to the variability in SWA. Findings indicate that distinct scale-free and oscillatory measures of sleep EEG could provide composite measures of sleep dynamics with low redundancy, potentially affording new insights into sleep regulatory processes in future studies.