The Interactive ‘Social Brain’: Behavioral and Neural Substrates for the Processing of Potential Engagement in Motor Interactions

Over the past three decades, the ’Social Brain’ model in cognitive neuroscience has emphasized a division between abstract mentalizing processes (MENTA network) and sensorimotor encoding of others’ actions (Mirror Neuron System, MNS). This separation, however, limits our understanding of social cognition, particularly in interactive contexts. ’Second-person Neuroscience’ suggests that direct engagement in social interactions recruits different neural and behavioral resources for interpreting others’ intentions. We examined this by studying markers of social intent in motor and facial cues, comparing individualistic (grasp to place) and social (grasp to pass) actions. Kinematic analysis showed that social grasps were slower, more precise, and more predictive for observers, with hand positioning signaling social intention, potentially linked to affordance processing. Eye-tracking confirmed the face as the most attended feature during action observation. In an fMRI follow-up, stimuli were used to assess neural responses to social intention and engagement-related features. Action-directedness, not social intent, primarily activated premotor, temporal, and occipital areas, while engagement ratings were associated with increased sensorimotor simulation. Representational Similarity Analysis showed shared engagement coding between MNS and TPJ, with right-lateralized regions focusing on engagement and left-lateralized areas on goals. These findings reveal key neural mechanisms for engagement in observed social actions.