The causal role of temporoparietal junction in computing social influence in human decision-making

Decision-making in social contexts is commonly driven by two major sources of social influence: normative influence and informational influence. Our previous work has dissociated these two types of social influence, and have identified that bilateral temporoparietal junction (TPJ) encodes normative influence. However, it remains unclear whether the effect of normative influence causally depends on activity in the TPJ. Here, we present a transcranial magnetic stimulation (TMS) study using a similar paradigm in a within-subject design (i.e., right TPJ, left TPJ, and vertex). Behavioral results indicate that disrupting activity in the left TPJ resulted in reduced choice switch probability (i.e., less influenced by dissenting social information), relative to the right TPJ and vertex conditions. Computational modeling with hierarchical Bayesian parameter estimation suggests that the corresponding parameter quantifying normative influence significantly decreased in the left TPJ condition. However, the extent to which informational influence (i.e., social learning) was integrated into individuals’ valuation processes was comparable in all three conditions. Together, our results provide evidence for the causal role of left TPJ in computing normative social influence in human decision-making, whereas the integration of informative social influence in value computation remains intact.