Most people are generous, but not toward everyone alike: generosity usually declines with social distance between individuals, a phenomenon called social discounting. Despite the pervasiveness of social discounting, social distance between actors has been surprisingly neglected in economic theory and neuroscientific research. We used functional magnetic resonance imaging (fMRI) to study the neural basis of this process to understand the neural underpinnings of social decision making. Participants chose between selfish and generous alternatives, yielding either a large reward for the participant alone, or smaller rewards for the participant and another individual at a particular social distance. We found that generous choices engaged the temporoparietal junction (TPJ). In particular, the TPJ activity was scaled to the social-distance-dependent conflict between selfish and generous motives during prosocial choice, consistent with ideas that the TPJ promotes generosity by facilitating overcoming egoism bias. Based on functional coupling data, we propose and provide evidence for a biologically plausible neural model according to which the TPJ supports social discounting by modulating basic neural value signals in the ventromedial prefrontal cortex to incorporate social-distancedependent other-regarding preferences into an otherwise exclusively own-reward value representation.social discounting | prosocial choice | fMRI | connectivity | neuroeconomics P rosociality is one of the most fundamental qualities of all human societies. Without the ability to take other people's interests into account, human relationships would disintegrate and societies would malfunction. It has been widely demonstrated in laboratory and field experiments that individuals consider the welfare of others in their decisions and the consequences a decision has on them (1-3). Although almost all of us behave prosocially at times, it is clear that people are not equally generous to everyone alike. Rather, generosity decreases as a function of the closeness of the relationship between two individuals (2, 4). However, it is currently unknown how social distance contributes to the decision process on a neural level. In the present study, we set out to address this question.Our first aim was to investigate the systematic influence of social-distance-dependent levels of generosity on neural activation. This was investigated using a social discounting experiment adapted to the functional magnetic resonance imaging (fMRI) environment (1). We measured blood oxygen leveldependent (BOLD) responses while subjects made choices between selfish and generous rewards for themselves and for other people that varied in social distance. Choosing selfishly yielded a payoff only for the subject, whereas making a generous choice resulted in a lower payoff for the subject coupled with a reward for another person at a specific social distance (Fig. 1). Next, based on the individual choices, we reconstructed the socialdistance-dependent other-regarding utility (ORU), tha...