The role of ventromedial prefrontal cortex and temporo-parietal junction in third-party punishment behavior

Third parties punish, sacrificing personal interests, offenders who violate either fairness or cooperation norms. This behavior is defined altruistic punishment and the degree of punishment typically increases with the severity of the norm violation. An opposite and apparently paradoxical behavior, namely anti-social punishment, is the tendency to spend own money to punish cooperative or fair behaviors. Previous fMRI studies correlated punishment behavior with increased activation of brain areas belonging to the reward system (e.g. the ventromedial prefrontal cortex, VMPFC), the mentalizing (e.g. the temporoparietal junction, TPJ) and central-executive networks. In the present study, we aimed at investigating the causal role of VMPFC and TPJ in punishment behaviors through the application of anodal transcranial direct current stimulation (tDCS). Sixty healthy participants were randomly assigned to three tDCS conditions: (1) anodal tDCS over VMPFC, (2) anodal tDCS over right TPJ (rTPJ), (3) sham stimulation. At the end of the stimulation, participants played a third-party punishment game, consisting in viewing a series of fair or unfair monetary allocations between unknown proposers and recipients. Participants were asked whether and how much they would punish the proposers using their own monetary endowment. To test membership effects, proposers and recipients could be either Italian or Chinese. Anodal tDCS over VMPFC increased altruistic punishment behavior whereas anodal tDCS over rTPJ increased anti-social punishment choices compared with sham condition, while membership did not influence participant's choices. Our results support the idea that the two types of punishment behaviors rely upon different brain regions, suggesting that reward and mentalizing systems underlie, respectively, altruistic and anti-social punishment behaviors.