Abstract
Observing social touch evokes a strong social-affective response. Our ability to extract the social-affective meaning of observed touch is supported by enhanced communication between brain networks, including social brain regions and somatosensory cortex. Yet, the direction of information flow across these networks and the overall neural dynamics of these processes remain unknown. The current study uses electroencephalography (EEG) to uncover how representations unfold spatial-temporally in the brain during touch observation. Twenty participants watched 500 ms video clips showing social and non-social touch during EEG recording. Representational similarity analysis reveals that EEG neural patterns are explained by visual features beginning at 90 ms post video onset. Social-affective features are processed shortly after, explaining neural patterns beginning at 150 ms. Next, we tracked the spatial-temporal neural dynamics by combining the EEG data with fMRI data from our prior study. We examined information flow across three key brain regions: early visual cortex (EVC), temporoparietal junction/posterior superior temporal sulcus (TPJ/pSTS), and somatosensory cortex. We find that neural information first arises in EVC 50 ms post video onset, then is processed by TPJ/pSTS at 110 ms, and finally somatosensory cortex at 190 ms. Lastly, variance partitioning analysis reveals that EEG neural patterns are uniquely explained by EVC 94 ms post video onset, then by TPJ/pSTS at 190 ms. EEG signals in TPJ/pSTS contain information about sociality of the video clips. Importantly, somatosensory cortex does not explain any unique variance but shares variance with TPJ/pSTS in explaining the EEG data. These results suggest that social touch is processed quickly by the brain, within the timeframe of feedforward visual processes. Social-affective meaning of observed touch is first extracted by social vision and followed by the later involvement of somatosensory simulation. This fast processing may underlie our ability to quickly and effectively use social touch for interpersonal communication.