State-dependent TMS of inferior frontal and parietal cortices highlights integration of grip configuration and functional goals during action recognition

Understanding the object-directed actions of conspecifics not only implies recognition of the object (e.g., a pen) and processing of the motor components (e.g., grip configuration), but also identification of the functional goal of the action (e.g., writing). Motor components and goal representations are both known to be critically involved in action recognition, but how the brain integrates these two pieces of information remains unclear. Action priming was used to tune the cognitive system to the integration of grip and goal representations. We evaluated the effect of briefly presented primes sharing grip and/or goal information with the target on recognition of action photographs. Single-pulse transcranial magnetic stimulation (TMS) was applied at target onset over the inferior frontal cortex (IFC) or the inferior parietal lobule (IPL) to evaluate their involvement in integrating grip and goal information. IFC and IPL stimulation specifically reduced integration of these two pieces of information. These results demonstrate, for the first time, the existence of specialized neuronal populations dedicated to grip/goal integration within a fronto-parietal network, supporting the importance given to this network by sensorimotor and predictive models of action recognition.