Pupil size reveals arousal level dynamics in human sleep

Abstract

Recent animal research has revealed the intricate dynamics of arousal levels that are potentially crucial for maintaining proper sleep resilience and memory consolidation. Also in humans, changes in arousal level are believed to be a determining characteristic of healthy and pathological sleep but tracking arousal fluctuations has been methodologically challenging. Here we measured pupil size, an established indicator of arousal levels, during overnight sleep and tested whether the arousal level affects cortical response to auditory stimulation. We show that pupil size dynamics change as a function of sleep macrostructure and microstructural events. In particular, pupil size is inversely related to the occurrence of sleep spindle clusters, a marker of sleep resilience. Additionally, pupil size prior to auditory stimulation influences the evoked response, most notably in delta power, a marker of several restorative and regenerative functions of sleep. Recording pupil size dynamics provides novel insights into the interplay between arousal levels and sleep oscillations, opening new avenues for future research and clinical applications in diagnosing and treating pathological sleep associated with abnormal arousal levels.