Striatal Social Reward Sensitivity Predicts Trust-Related Brain Responses Depending on Closeness and Depression.

AIM: Depression is associated with social dysfunction, but the mechanisms linking affective symptoms to disrupted close relationships remain understudied. It is also unclear whether neural sensitivity to shared reward predicts social valuation during more complex interactions, with the possibility of depression altering the link between how people experience rewards shared with and trust reciprocated by close others. Thus, this preregistered fMRI study tested whether neural sensitivity to shared reward cross-task predicts trust-related behavior and brain responses, and whether these associations depend on perceived closeness and depressive symptoms. METHODSX: Participants completed a reward-sharing task and a Trust Game with a close friend, a stranger, and a computer. We measured striatal shared reward sensitivity (SRS; friend > computer) and tested whether it related to investment behavior and brain responses to trust reciprocation. Depressive symptoms and perceived closeness were assessed via self-report. RESULTS: In a final sample of n = 123, participants reporting more depressive symptoms invested more in their friend than in the computer. Striatal SRS predicted temporoparietal junction responses to reciprocated trust, but this association depended jointly on social closeness and depression - with depression reversing the expected pattern among individuals reporting closer relationships. Striatal SRS was also inversely associated with connectivity between the default mode network and cerebellum during reciprocity. CONCLUSIONS: These findings suggest that closeness calibrates the striatal SRS' link to regional activity and network-level responses during social exchange, while depression alters how striatal SRS relates to regional activity, potentially disrupting how individuals interpret and respond to close others.