Seeing the Unexpected: How Brains Read Communicative Intent through Kinematics

Social interaction requires us to recognize subtle cues in behavior, such as kinematic differences in actions and gestures produced with different social intentions. Neuroscientific studies indicate that the putative mirror neuron system (pMNS) in the premotor cortex and mentalizing system (MS) in the medial prefrontal cortex support inferences about contextually unusual actions. However, little is known regarding the brain dynamics of these systems when viewing communicatively exaggerated kinematics. In an event-related functional magnetic resonance imaging experiment, 28 participants viewed stick-light videos of pantomime gestures, recorded in a previous study, which contained varying degrees of communicative exaggeration. Participants made either social or nonsocial classifications of the videos. Using participant responses and pantomime kinematics, we modeled the probability of each video being classified as communicative. Interregion connectivity and activity were modulated by kinematic exaggeration, depending on the task. In the Social Task, communicativeness of the gesture increased activation of several pMNS and MS regions and modulated top-down coupling from the MS to the pMNS, but engagement of the pMNS and MS was not found in the nonsocial task. Our results suggest that expectation violations can be a key cue for inferring communicative intention, extending previous findings from wholly unexpected actions to more subtle social signaling.