Neural correlates of observing joint actions with shared intentions

Studies on the neural bases of action perception have largely focused on the perception of individual actions. Little is known about perception of joint actions where two or more individuals coordinate their actions based on a shared intention. In this fMRI study we asked whether observing situations where two individuals act on a shared intention elicits a different neural response than observing situations where individuals act on their independent parallel intentions. We compared the neural response to perceptually identical yet intentionally ambiguous actions observed in varying contexts. A dialog between two individuals conveyed either a shared intention or two independent parallel intentions. The dialogs were followed by an identical video clip where the two individuals performed certain actions. In one task condition participants tracked the intentions of the actors, in the other, they monitored moving colored dots placed on the same videos. We found that in the intention task versus the color task, observing joint actions based on shared intentions activated the temporal poles, precuneus, and the ventral striatum compared to observing interactions based on parallel intentions. Precuneus and the temporal poles are thought to support mental state reasoning, the latter with a more specific role in retrieving memories associated with social scripts. Activation in the ventral striatum, an area involved in reward processing, likely indicates a hedonistic response to observed shared intentional relations similarly to those experienced when personally sharing mental states with others.