Perceiving Hesitation requires both the Motor and Mentalizing systems

Abstract

The mentalizing network and the putative mirror neuron system (pMNS) are two important large scale brain networks for social cognition, with very little overlap between them. Evidence suggests however that the two networks can collaborate for understanding the state of mind of others on the basis of their body movements. Here using fMRI we find that when participants view hand actions to detect hesitations they activate both their mentalizing and pMNS networks and information is exchanged across these networks. In a follow-up experiment using repetitive TMS we find that disturbing activity in either network slows hesitation attribution. In contrast, watching the same actions to determine the size of the object being grasped only triggered activity in the pMNS network, and rTMS over the mentalizing network then no longer slowed reactions. When we see others actions, we recruit our own motor system. Our results suggest that for detecting a simple mental state like hesitation, this pre-processed motor information becomes a necessary input into a mentalizing network that is essential for associating deviations from a predicted motor program with a specific mental state.