Spectrally resolved EEG intersubject correlation reveals distinct cortical oscillatory patterns during free-viewing of affective scenes

The analysis of the similarity of the brain response of different individuals using intersubject correlation (ISC) can be used to uncover the neural mechanisms behind the processing of complex audiovisual stimuli, and to understand how the brain works in real-life situations. Previous research on ISC reported anecdotal evidence of larger ISC during emotional scenes compared to neutral ones, but this effect has not been systematically investigated using standardized emotional movies. Moreover, the complex interplay between neuronal populations oscillating at different timescales was mainly studied through fMRI, thus with limited temporal resolution. This study aimed at showing how emotional movies synchronize brain activity in the main frequency bands characterizing cortical activity. Thirty-nine participants watched 18 movie clips selected from a standardized database of emotional movies (E-MOVIE) while their EEG activity was recorded. Spectrally resolved ISC was computed based on the coherence of homologous channels for each possible subject pair in the Delta, Alpha, and Gamma bands. Permutation-based statistics revealed that all emotional categories prompted larger ISC compared to the Neutral in each band. Moreover, high arousal erotic and fearful scenes prompted larger Delta-ISC and Gamma-ISC compared to the other categories. Finally, ISC topography followed a spatial gradient. At slower frequencies, ISC involved wider regions of the scalp, becoming more restricted to occipito-parietal regions at higher frequencies. Taken together, these results show that emotions trigger brain synchronization between individuals at multiple spatial and spectral scales. Different emotional states are reflected in specific topographical patterns of ISC in different frequency bands.