Reafferent copies of imitated actions in the right superior temporal cortex

Imitation is a complex phenomenon, the neural mechanisms of which are still largely unknown. When individuals imitate an action that already is presen t in their motor repertoire, a mechanism matching the observed action onto an internal motor representation of that action should suffice for the purp ose. When one has to copy a new action, however, or to adjust an action pre sent in one's motor repertoire to a different observed action, an additiona l mechanism is needed that allows the observer to compare the action made b y another individual with the sensory consequences of the same action made by himself. Previous experiments have shown that a mechanism that directly matches observed actions on their motor counterparts exists in the premotor cortex of monkeys and humans. Here we report the results of functional mag netic resonance experiments, suggesting that in the superior temporal sulcu s, a higher order visual region, there is a sector that becomes active both during hand action observation and during imitation even in the absence of direct vision of the imitator's hand. The motor-related activity is greate r during imitation than during control motor tasks. This newly identified r egion has all the requisites for being the region at which the observed act ions, and the reafferent motor-related copies of actions made by the imitat or, interact.