Selective virtual lesions of somatosensory and motor underpinnings of action simulation

Mere action observation may trigger a mental simulation process that is reflected in the activation of fronto-parietal sensorimotor circuits for making the same action. This occurs not only during observation of naturalistic movements but also when viewing biomechanically impossible movements that tap the afferent component of action, possibly by eliciting strong somatic feelings in the onlooker. Information on the possible causative role of frontal and parietal structures in simulating motor and sensory action components is lacking. By combining low-frequency repetitive and single-pulse transcranial magnetic stimulation we found that virtual lesions of ventral promotor cortex (vPMc) and primary somatosensory cortex (S1) suppressed motor facilitation contingent upon observation of possible and impossible movements respectively. In contrast, virtual lesions of the primary motor cortex did not influence mirror motor facilitation. The reported double dissociation suggests that vPMc and S1 play an active, differential role in simulating efferent and afferent components of observed actions.