The Sound of Actions in Apraxia

Studies in nonhuman and human primates have demonstrated that sound-producing actions are mapped on the same mirror circuits that are activated during the visual recognition and execution of actions [1-12]. However, no causative link between the auditory recognition and execution of actions has been provided thus far. Here, we sought to determine whether patients with apraxia, who are by definition impaired in performing specific gestures, are also impaired in recognizing sounds specifically linked to human actions. Twenty-eight left-hemisphere-damaged patients with or without limb and/or buccofacial apraxia and seven right-hemisphere-damaged patients with no apraxia were asked to match sounds evoking human-related actions or nonhuman action sounds with specific visual pictures. Hand and mouth action-related sound recognition were specifically impaired in limb and buccofacial apraxia patients, respectively. Lesional mapping revealed that the left frontoparietal cortex is crucial for recognizing the sound of limb movements. By contrast, the left inferior frontal gyrus and adjacent insular cortex are causatively associated with recognition of bucco-facial-related action sounds. These behavioral and neural double dissociations indicate that a left-lateralized multi-modal mirror network is actively involved in the body-part-specific motor mapping of limb and mouth action-related sounds, as well as in the execution of the very same actions.