Inferring deceptive intentions through the mentalizing system: a TMS priming study

The ability to infer intentions from verbal and nonverbal behavior is critical for everyday social life. By combining single-pulse Transcranial Magnetic Stimulation (TMS) with a priming paradigm, we tested whether the Mentalizing System mediates the influence that prior verbal information about a moving agent exerts on the ability to judge her/his intentions from observed kinematics. We used a modified version of the Faked-Action Discrimination Task (FAD), a forced-choice paradigm in which participants watched videos of actors lifting a cube and judged whether the actors were trying to deceive them concerning the real weight of the cube. Videos could be preceded or not by verbal information (priors) about the agent’s truthful or deceitful intent. We applied a TMS single pulse over the dorsomedial Prefrontal Cortex (dmPFC), the right posterior Superior Temporal Sulcus (pSTS) and the right Temporo-Parietal Junction (rTPJ). Sham-TMS was used as control. We observed no influence of priors on FAD performance following sham and rTPJ stimulations. In contrast, following dmPFC stimulation, and to a lesser extent pSTS stimulation, we observed that priors produced a congruent biasing influence on the ability to discriminate between truthful and fake movements. These TMS facilitatory effects were selective for prior information about the actors’ deceptive intentions. These findings highlight a functional role of dmPFC and, to a lesser extent of pSTS, in coupling prior information about deceptive intents with action observation. Our study provides a causal evidence that fronto-temporal nodes of the Mentalizing System are functionally relevant to mental state inference during action observation.