Dissociable roles of left and right temporoparietal junction in strategic competitive interaction.

Although many studies have shown that the temporoparietal junction (TPJ) is involved in inferring others' beliefs, neural correlates of 'second-order' inferences (inferring another's inference about one's own belief) are still elusive. Here we report a functional magnetic resonance imaging experiment to examine the involvement of TPJ for second-order inferences. Participants played an economic game with three types of opponents: a human opponent outside the scanner, an artificial agent that followed a fixed probabilistic strategy according to a game-theoretic solution (FIX) and an artificial agent that adjusted its choices through a machine-learning algorithm (LRN). Participants' choice behaviors against the human opponent and LRN were similar but remarkably different from those against FIX. The activation of the left TPJ (LTPJ) was correlated with choice behavior against the human opponent and LRN but not against FIX. The overall activity pattern of the LTPJ for the human opponent was also similar to that for LRN but not for FIX. In contrast, the right TPJ (RTPJ) showed higher activation for the human opponent than FIX and LRN. These results suggest that, while the RTPJ is associated with the perception of human agency, the LTPJ is involved in second-order inferences in strategic decision making.