Distinct roles of the medial prefrontal cortex in advantageous and disadvantageous inequity aversion

Human beings have a strong preference for the fair distribution of resources in situations of both advantageous and disadvantageous inequity. Neuroimaging studies have shown that the process of advantageous and disadvantageous inequity aversion involves distinct brain regions. However, little is known about the causal roles of the dorsal medial prefrontal cortex (dmPFC) in these two types of inequity aversion. To clarify the roles of the dmPFC in both types of inequity aversion, 70 subjects were recruited and randomly assigned to two anodal transcranial direct current stimulation (tDCS) groups: tDCS over the dmPFC and tDCS over the primary visual cortex. Participants then completed a dictator game, which was used to measure the aversion to inequity. This study found that tDCS over the dmPFC decreased the aversion to disadvantageous inequity, but not that to advantageous inequity, and the treatment effect was modulated by equity cost. These results show that the dmPFC plays different roles in these two types of inequity aversion.