Antarctic polar night brings extreme light deprivation, prolonged isolation and severe circadian disruption, yet longitudinal resting-state electroencephalography (EEG) signatures reflecting neurophysiological alterations in this harsh environment remain poorly characterized. In this exploratory longitudinal research, resting-state EEG recordings with eyes open (EO) and eyes closed (EC) were acquired from 16 Antarctic expeditioners at four mission stages: pre-departure, pre-polar-night, early post-polar-night, and austral summer. Linear mixed-effects models with false discovery rate correction were applied to analyze delta eyes-closed/open differentiation (the EC-EO delta log-power difference), delta sub-bands, aperiodic spectral features, entropy, EEG microstates and delta-band functional connectivity. The delta EC-EO difference exhibited consistent, progressively negative shifts in parietal, frontal, whole-brain and occipital regions across the expedition timeline, with the most pronounced shifts observed in recordings obtained during and after the polar-night period; this effect spanned all slow, mid and fast delta sub-bands. Secondary mild temporal variations were observed in aperiodic spectral metrics, occipital sample entropy and global delta connectivity, whereas EEG microstates displayed no significant longitudinal alterations. Collectively, the delta EC-EO difference emerges as a candidate EEG index of resting-state condition differentiation in the low-frequency range, pending validation in larger studies with synchronized behavioral, physiological, and environmental measures.
