Understanding interpersonal action coordination: an fMRI study.

Coordination of actions according to the request of another person is frequently observed in daily life. The purpose of this study is to elucidate the neural mechanisms related to the processing of this type of interpersonal action coordination by using functional magnetic resonance imaging (fMRI). In the first experiment, participants viewed movie clips depicting two people (1st and 3rd person) involved in a joint-action situation: one person (passive agent) holding two objects asked the other person to take one object; the other person (active agent) then performing a congruent or incongruent action with regard to the request. fMRI results showed that the right inferior frontal gyrus (IFG) and right cerebellum were more activated during the observation of incongruent actions than that of congruent actions. Greater activation in the right posterior superior temporal sulcus (pSTS) and the medial prefrontal cortex (mPFC) were also found in the same contrast after small volume correction (SVC). In the second experiment, in which only the active person appeared in the movie clip (single-action situation), no significant activation in the right IFG and right cerebellum was found, although greater activation in the right pSTS and the mPFC was found during the observation of the incongruent action than that of the congruent action after SVC. Our study suggests that the right IFG, which is assumed to be a part of the mirror neuron system, is involved in understanding interpersonal action congruency.