Trust plays an important role during adolescence for developing social relations. Although prior developmental studies give us insight into adolescents' development of differentiation between close (e.g., friends) and unknown (e.g., unknown peers) targets in trust choices, less is known about the development of trust to societal targets (e.g., members of a community organization) and its underlying neural mechanisms. Using a modified version of the Trust Game, our preregistered fMRI study examined the underlying neural mechanisms of trust to close (friend), societal (community member), and unknown others (unknown peer) during adolescence in 106 participants (aged 12–23 years). Adolescents showed most trust to friends, less trust to community members, and the least trust to unknown peers. Neural results show that target differentiation in adolescents' trust behavior is associated with activity in social brain regions implicated during mentalizing, reward processing, and cognitive control. Recruitment of the medial prefrontal cortex (mPFC) and OFC was higher for closer targets (i.e., friend and community member). For the mPFC, this effect was most pronounced during no trust choices. Trust to friends was additionally associated with increased activity in the precuneus and bilateral temporal parietal junction. In contrast, bilateral dorsolateral prefrontal cortex and anterior cingulate cortex were most active for trust to unknown peers. The mPFC showed increased activity with age and consistent relations with individual differences in feeling needed/useful.

Giving is often characterized by the conflicting decision to give up something of value to benefit others. Recent evidence indicated that giving is highly context-dependent. To unravel the neural correlates of social context, in this study, young adults ( n = 32) performed a novel giving fMRI paradigm, in which they divided coins between self and known (friends) or unknown (unfamiliar) others. A second manipulation included presence of others; giving decisions were made with an audience or anonymously. Results showed that participants gave more coins to a friend than to an unfamiliar other and generally gave more in the presence of an audience. On a neural level, medial prefrontal cortex and the right insula were most active for relatively generous decisions. These findings possibly reflect that aversion of norm deviation or fairness concerns drive differences in the frequency of giving. Next, activation in separate subregions of the TPJ-IPL (i.e., a region that comprises the TPJ and inferior parietal lobule) was found for target and audience contexts. Overall, our findings suggest that donation size and social contextual information are processed in separable brain regions and that TPJ-IPL plays an important role in balancing self- and other-oriented motives related to the social context.