History of interaction and task distribution modulate action simulation.

Recent work suggests that social interaction modulates the sensorimotor simulation of an observed action. Recording electroencephalograms during a triadic social interaction, we investigated the effects of two specific aspects of social interaction on action simulation: the recent history of interaction and the distribution of individual parts of a simple joint task between actors. Activation of sensorimotor areas was larger during observation of the individual action of an interaction partner compared to observation of the same action of a person performing only individual actions, unless this person had interacted with the observer in the recent past. In addition, it is likely that the participants simulated the action onset of the individual actions of their interaction partner, but only when their partner was the one who initiated the joint action. These results demonstrate that action simulation can be modulated by present and past interactions between the actor and the observer and by how a joint task is distributed between actors.