Neural Modulation of Social Distance on Third-Party Punishment

As a crucial mechanism to enforce social norms, people as third parties tend to punish the norm violators even it costs their own pay-off. However, people do not usually treat everyone equally, e.g., it is shown that people are nice to close others. Here, we investigated how third party punishment (TPP) and its neural correlates is modulated by social distance (SD) by using fMRI. Behaviorally, participants punished more when the unfair perpetrator was more distant to them. Such SD-modulation effect was stronger when the punishment was free. Model-based results showed that SD-dependent computational signals were encoded in right dlPFC. More interestingly, SD modulated the relationship between punishment levels and neural activities in default network including vmPFC and bilateral hippocampus. The explorative functional connectivity analysis further showed that the vmPFC increased the association with left dlPFC when participants punished close others. Finally, punishment type (costly vs. free) also modulated the relationship between punishment levels and neural correlates in dACC and the ventral striatum. Taken together, our results revealed the neurocomputational underpinnings of how SD plays an important role in affecting TPP.