0944 Lower Sleep Spindle Density and Evening Chronotype are Associated with Increased Daytime Sleepiness in Adolescents

Abstract Introduction Insufficient sleep and daytime sleepiness are widespread among adolescents, contributing to academic difficulties, mood disturbances, and safety risks. Beyond total sleep duration, neurophysiological and circadian factors may play a critical role. The objective of the present study was to simultaneously examine the relative contributions of key sleep parameters (duration, neurophysiology, and chronotype) that are known to change during adolescence to daytime sleepiness, under typical school-week conditions in adolescents’ natural environments Methods Forty-five healthy adolescents (27 girls, 18 boys; mean age = 13.9 SD= 0.95) were included. Participants completed multi-night actigraphy, daily electronic sleep logs, and a single overnight in-home electroencephalography (EEG) recording using a multichannel frontopolar EEG device (Sleep Profiler). Daytime sleepiness was assessed using the Epworth Sleepiness Scale for Children and Adolescents (ESS-CHAD). Actigraphic data were scored using Actiware software; Raw EEG signals were visually analyzed and scored using standardized AASM scoring criteria. Demographic information, including pubertal status and gender, was collected via a detailed background questionnaire. Results Regression analyses, adjusted for age and sex, were performed to identify unique correlates of daytime sleepiness. The findings revealed that lower sleep spindle density and a stronger evening circadian preference were the only significant variables associated with daytime sleepiness. These two factors together were strongly associated with sleepiness, explaining 45.3% of the variance in subjective daytime sleepiness. Conclusion Adolescent daytime sleepiness is strongly associated with neurophysiological (sleep spindle density) and circadian (chronotype) factors, suggesting that sleep duration alone is insufficient to explain sleepiness in this population. Interventions aimed at improving sleep health in adolescents should consider targeting both sleep microstructure and chronotype Support (if any) This work was supported by The Azrieli Centre for Autism Research award, the NSERC Discovery Grant RGPIN-2021-03363, and the Canadian Institute of Health Research, Grant#166148 to Reut Gruber.