Accepting unfairness by a significant other is associated with reduced connectivity between medial prefrontal and dorsal anterior cingulate cortex.

Conflict is a ubiquitous feature of interpersonal relationships, yet many of these relationships preserve their value following conflict. Our ability to refrain from punishment despite the occurrence of conflict is a characteristic of human beings. Using a combination of behavioral and neuroimaging techniques, we show that prosocial decision-making is modulated by relationship closeness. In an iterated social exchange, participants were more likely to cooperate with their partner compared to an unknown person by accepting unfair exchanges. Importantly, this effect was not influenced by how resources were actually being shared with one's partner. The medial prefrontal cortex (MPFC) was activated when the partner, rather than the unknown person, behaved unfairly and, in the same context, the MPFC demonstrated greater functional connectivity with the dorsal anterior cingulate cortex (DACC). MPFC-DACC connectivity was inversely associated with participants' tendency to "forgive" their partner for unfairness as well as performance outside the scanner on a behavioral measure of forgiveness. We conclude that relationship closeness modulates a neural network comprising the MPFC/DACC during economic exchanges.