Despite the importance of valuing another person's welfare for prosocial behavior, currently we have only a limited understanding of how these values are represented in the brain and, more importantly, how they give rise to individual variability in prosociality. In the present study, participants underwent functional magnetic resonance imaging while performing a prosocial learning task in which they could choose to benefit themselves and/or another person. Choice behavior indicated that participants valued the welfare of another person, although less so than they valued their own welfare. Neural data revealed a spatial gradient in activity within the medial prefrontal cortex (MPFC), such that ventral parts predominantly represented self-regarding values and dorsal parts predominantly represented other-regarding values. Importantly, compared with selfish individuals, prosocial individuals showed a more gradual transition from selfregarding to other-regarding value signals in the MPFC and stronger MPFC-striatum coupling when they made choices for another person rather than for themselves. The present study provides evidence of neural markers reflecting individual differences in human prosociality.R anging from small acts of kindness in daily life to self-sacrificing altruism under life-threatening situations, we often observe large individual differences in how humans value another person's welfare. This differential valuation process seems to be the key to understanding various human prosocial behaviors, which are fundamental to the sustainability of human society (1). The underlying neural mechanisms and their relationship to individual differences in prosociality remain unclear, however.Perhaps the most powerful way of assessing how an outcome is valued is to use an instrumental learning paradigm that examines whether the occurrence of a response increases when it is followed by that outcome (2). The mechanisms underlying this type of learning have been described more formally with a computational model, known as the advantage learning model (3-5), which has been used successfully to reveal the neuroanatomical substrates of subjective valuation (3,4,6). Previous research has further refined the neurobiological model of reinforcement learning by emphasizing the specific roles played by the medial frontal cortex and the striatum; the medial frontal cortex computes the value of the chosen action, whereas the striatum processes reward prediction errors during reinforcement learning (4, 6-10).Unlike our current understanding of the valuation process for self-regarding choices (3, 6-12), it is much less clear whether learning also can be driven by other-regarding values, and whether this other-regarding valuation relies on the same mechanisms of reinforcement learning as those used for self. Moreover, despite the rapidly accumulating research on reward processing in social domains (13-19), the question remains of how neural representation of self-regarding vs. other-regarding values is related to individual differen...