Favouritism in the sensorimotor system: Social interaction modulates predictive action simulation

The ability to anticipate others’ actions is crucial for social interaction. We have recently showed that one simulates in advance an action performed by an interaction partner and practically ignores the same action performed by a person that (s)he never interacts with (Kourtis et. al., Biology Letters, 2010). In a recent follow-up experiment we explored the effects of interaction history on action simulation. Similar to the previous study, the setup comprised of an EEG participant, an interaction partner and an “outsider” (i.e. a person only performing individual actions). The task of the EEG participant was to plan and perform an individual action (lifting an object) or a joint action (giving or receiving an object) or to anticipate to observe the same individual action performed by either the partner or the “outsider”. The EEG participant had the role of the giver or the receiver in the 1st half of the experiment and the opposite role in the 2nd half; moreover, the partner in one half became the “outsider” in the other half (and vice versa). In the 1st half of the experiment, we recorded stronger mu rhythm (8–12 Hz) decrease over sensorimotor cortex before and especially during observation of the early stages of the partner’s action compared to the outsider’s (identical) action. No difference between the partner’s and outsider’s actions was recorded in the 2nd half of the experiment. These findings strengthen the notion that one’s sensorimotor system favours the actions of an interaction partner over the same actions performed by an “outsider”; however, this favouritism disappears when the outsider has interacted with the observer in the past.