Ventral premotor and inferior parietal cortices make distinct contribution to action organization and intention understanding

It is well known that ventral premotor area F5 codes the goal of executed and observed motor acts. This area is anatomically connected with part of the inferior parietal cortex (area PFG), which has been recently shown to play a role in action organization and intention understanding. The aims of the present study were 1) to assess whether the discharge of F5 motor neurons and mirror neurons (MNs) codes action goals and 2) to clarify the relative contribution of F5 and PFG in action organization and intention understanding. To this purpose, we first recorded from F5 motor neurons and MNs of 2 monkeys while performing a motor task constituted by 2 actions ("grasp-to-eat" and "grasp-to-place") or observing the same task done by an experimenter. Results showed that some F5 neurons code grasping according to the goal of the action in which it is embedded. Subsequently, we recorded from PFG motor neurons and MNs of the same monkeys, using the same tasks. The comparison between the neuronal properties of F5 and PFG motor neurons suggests that PFG plays a major role in organizing natural actions. Furthermore, the similarities between MNs properties of the 2 areas indicate that they constitute a functional circuit underlying others' intention understanding.