Exploration of EEG activity corresponding to the functional expansion theory of disgust

Disgust is often conceptualised as a basic emotion arising from contamination avoidance; however, the functional expansion account distinguishes multiple disgust domains that differ in their social meanings and behavioural outcomes. This study investigated whether core disgust, animal-reminder disgust, and moral disgust exhibit distinct whole-brain temporal dynamics indexed by electroencephalography (EEG) microstates. Forty university students viewed seven video clips eliciting the three disgust types and neutral affect while their EEG activity was recorded. They also completed tests of emotional state and disgust sensitivity. EEG microstate analysis was used to identify four canonical microstate classes and quantify their temporal and transition indices across conditions. An exploratory machine-learning analysis using L1-regularised logistic regression was also conducted to identify candidate microstate features differentiating disgust from neutral conditions. The mean duration of microstate D made the strongest positive contribution to disgust classification. Subsequent linear mixed-effects models indicated an uncorrected tendency towards longer microstate D duration for moral disgust than that for neutral affect, although this effect was deemed insignificant after FDR correction. Exploratory comparisons among disgust conditions further suggested longer microstate D duration during moral and animal-reminder disgust than that observed for core disgust; however, the corrected main effect of disgust type was insignificant. These findings suggest that microstate D duration may reflect disgust-related temporal dynamics, particularly for stimuli requiring more elaborate appraisals, such as moral and animal-reminder disgust. Although the observed effects were exploratory and not robust after correction for multiple comparisons, we demonstrate the potential utility of EEG microstate analysis for examining the temporal organisation of complex disgust processing.