Tarailis, P.; Griskova-Bulanova, I.

Electroencephalographic (EEG) microstates provide a compact framework for characterizing the temporal organization of large-scale brain activity, yet their sensitivity to altered brain states remains insufficiently explored. In this study, we applied broadband and frequency-resolved EEG microstate analysis to resting-state EEG data from two publicly available datasets acquired under markedly different altered-state conditions: psilocybin microdosing and acute inhaled N,N-dimethyltryptamine (DMT). The aim was to determine whether narrowband microstate analysis reveals structured alterations in resting-state brain dynamics beyond those captured by broadband analysis alone. Psilocybin microdosing was associated with relatively subtle effects, including reduced global field power and frequency-specific alterations in delta- and theta-band microstate parameters, while no significant broadband spatiotemporal changes were observed. In contrast, acute inhaled DMT was associated with broader microstate alterations spanning broadband, delta, theta, and alpha activity, indicating more extensive reorganization of temporal microstate expression. Across both datasets, a descriptive overlap was observed in the delta band, where microstate C showed increased duration and microstate D showed decreased occurrence. Given the substantial differences between datasets in dose, route of administration, temporal dynamics, and study context, these overlapping effects should be interpreted cautiously. Overall, the findings support frequency-resolved EEG microstate analysis as a useful approach for characterizing altered resting-state brain dynamics and for detecting frequency-specific effects that may be obscured in broadband summaries.