The Effect of Oxytocin on Third-Party Altruistic Decisions in Unfair Situations: An fMRI Study

Humans display an intriguing propensity to help the victim of social norm violations or punish the violators which require theory-of-mind (ToM)/mentalizing abilities. The hypothalamic peptide oxytocin (OXT) has been implicated in modulating various pro-social behaviors/perception including trust, cooperation, and empathy. However, it is still elusive whether OXT also influences neural responses during third-party altruistic decisions, especially in ToM-related brain regions such as the temporo-parietal junction (TPJ). To address this question, we conducted a pharmacological functional magnetic resonance imaging experiment with healthy male participants in a randomized, double-blind, cross-over design. After the intranasal administration synthetic OXT (OXT^IN) or placebo (PLC), participants could transfer money from their own endowment to either punish a norm violator or help the victim. In some trials, participants observed the decisions made by a computer. Behaviorally, participants under OXT^IN showed a trend to accelerate altruistic decisions. At the neural level, we observed a strong three-way interaction between drug treatment (OXT/PLC), agency (self/computer), and decision (help/punish), such that OXT^IN selectively enhanced activity in the left TPJ during observations of others being helped by the computer. Collectively, our findings indicate that OXT enhances prosocial-relevant perception by increasing ToM-related neural activations.