Capturing continuous spectrotemporal pupil--brain coupling with simultaneous wearable EEG/Eye tracking

Abstract

Spontaneous fluctuations in pupil diameter are closely linked to neural dynamics, yet most evidence for pupil--brain coupling has been obtained in conventional laboratory settings. We therefore asked whether the spectrotemporal and directional organization of such coupling can be captured with wearable systems to test their use in naturalistic settings. Using combined lightweight mobile EEG (MUSE) and eye tracking (Tobii Pro Glasses 3) devices, we investigated resting-state pupil--brain coupling and explored interoceptive attention to determine whether the core organizational principles observed with stationary equipment are detectable within and preserved across continuous recording states. Cross-correlation, mutual information, and Granger causality analyses revealed that pupil--brain coupling displayed clear frequency-dependent organization. Lower EEG frequencies (2-12Hz) preceded pupil dynamics by roughly 764ms, while higher frequencies showed a distinct coupling range. Granger-causality analysis further indicated predominantly EEG-to-pupil directional coupling. Similar observations were made during interoception. Overall, these findings align well and extend previous evidence on spontaneous pupil--brain coupling, demonstrating that lightweight and movable wearable devices are suitable to characterize spectrotemporal and directional pupil--brain interactions. In turn, these results encourage future fundamental and translational research in naturalistic environments.