Mental simulation of action in the service of action perception.

We used the quantitative 14C-deoxyglucose method to map the activity pattern throughout the frontal cortex of rhesus monkeys, which either grasped a three-dimensional object or observed the same grasping movements executed by a human. We found that virtually the same frontal cortical networks were recruited for the generation and the perception of action, including the primary motor cortex (MI/F1), premotor cortical areas (F2, F5, and F6), the primary (SI) and supplementary (SSA) somatosensory cortex, medial cortical areas (8m and 9m), and the anterior cingulate. The overlapping networks for action execution and action observation support the notion that mental simulation of action could underlie the perception of others' actions. We suggest that the premotor and the somatotopic MI/F1 activations induced by action observation reflect motor grasp of the observed action, whereas the somatotopic SI and the SSA activations reflect recruitment of learned sensory-motor associations enabling perceptual understanding of the anticipated somatosensory feedback. We also found that the premotor activations were stronger for action observation, in contrast to the primary somatosensory-motor ones, which were stronger for action execution, and that activations induced by observation were bilateral, whereas those induced by execution were contralateral to the moving forelimb. We suggest that these differences in intensity and lateralization of activations between the executive and the perceptual networks help attribute the action to the correct agent, i.e., to the "self" during action execution and to the "other" during action observation. Accordingly, the "sense of agency" could be articulated within the core components of the circuitry supporting action execution/observation.