Common and distinct neural correlates of social interaction processing and theory of mind in narratives

Social interaction processing and theory of mind (ToM) frequently co-occur, but their commonalities and distinctions at behavioral and neural levels remain unclear. Participants (N = 231) provided moment-by-moment ratings of four text and four audio narratives on social interactions and ToM engagement, which were reliable (split-half r = 0.98 and 0.92, respectively) but only modestly correlated (r = 0.32). In a second sample (N = 90), we analyzed the co-variation between social interaction and ToM ratings and fMRI activity during text and audio narratives. Activity maps associated with social interaction processing and ToM generalized across text and audio (spatial r = 0.60 and 0.58, respectively) and overlapped in canonical ToM regions (FDR q < 0.01). ToM uniquely engaged the anterior intraparietal sulcus, right lateral occipitotemporal cortex, and right supplementary motor area. These results suggest that observing social interactions automatically engages canonical ToM regions, even without explicit mentalizing, and ToM additionally engages brain regions related to action understanding.