Neural responses to equity and inequity when receiving vicarious rewards for self and charity during adolescence.

The underlying mechanisms of increasing prosocial behavior to charity organizations during adolescence remain poorly understood. Here we investigated adolescents' neural sensitivity to equity and inequity outcome distributions for self and charity. In three longitudinal waves including participants between ages 11-24-years (wave 1: n = 160, 86 females; wave 2: n = 165, 84 females; wave 3: n = 174, 90 females), we studied neural responses in dorsolateral prefrontal cortex (DLPFC), temporal parietal junction (TPJ), and ventral striatum (VS). To this end, we used a fMRI paradigm in which participants received rewards either only for self, only for charity, for both, or for neither. Similar as in previous research, activity in the VS correlated with self-serving outcomes. In contrast, the DLPFC and TPJ showed lowest activity to equity outcomes (mutual benefit) and higher activity to both self-serving and charity-serving inequity, suggesting a general role in processing inequity. Finally, TPJ activity was highest when neither party received a reward, possibly signaling additional demands on social attention switching. Developmental comparisons revealed region-specific developmental trajectories, with stronger activity in VS for self-serving gains in early adolescence and stronger activity in DLPFC and TPJ for inequity gains in late adolescence. Together, these findings suggest a qualitative shift from personal reward-driven processing to more socially evaluative equity processing during adolescent development.