Differential role of the Mentalizing and the Mirror Neuron system in the imitation of communicative gestures.

Successful social interaction requires recognising the intention of another person's communicative gestures. At a neural level, this process may involve neural activity in different systems, such as the mentalizing system (MS) and the mirror neuron system (MNS). The aim of the present study was to explore the neural correlates of communicative gestures during observation and execution of these gestures. Twenty participants watched video clips of an actor executing social gestures (S), non-social gestures (NS) and meaningless gestures (ML). During fMRI data acquisition, participants were asked to observe (O) and subsequently to execute (E) one of two tasks: imitate the gesture presented (IMI) or perform a motor control task (CT). For the contrast IMI>CT we found activations in the core areas of the MNS [inferior parietal lobule (IPL) and inferior frontal cortex, the posterior part of pars opercularis], as well as in areas related to the MS [superior temporal sulcus (STS) and middle cingulate cortex]. For S>NS, we found activations in the left medial orbitofrontal cortex (mOFC), right superior frontal cortex and middle cingulate cortex. The interaction of stimulus condition (S vs NS) and task (IMI vs CT) revealed activation in the right IPL. For the interaction between observation vs execution (O vs E), task (IMI vs CT) and stimulus condition (S vs NS) we found activation in the right mOFC. Our data suggest that imitation is differentially processed in the MNS as well as in the MS. The activation in IPL is enhanced during the processing of social gestures most likely due to their communicative intention. The activation of IPL together with medial frontal areas may contribute to mentalizing processes. The interaction in the mOFC suggests an involvement of self-referential processes in the processing of social gesture.