As people form social groups, they benefit from being able to detect socially valuable community members-individuals who act prosocially, support others, and form strong relationships. Multidisciplinary evidence demonstrates that people indeed track others' social value, but the mechanisms through which such detection occurs remain unclear. Here, we combine social network and neuroimaging analyses to examine this process. We mapped social networks in two freshman dormitories (n = 97),

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... g how often individuals were nominated as socially valuable (i.e., sources of friendship, empathy, and support) by their peers. Next, we scanned a subset of dorm members ("perceivers"; n = 50) as they passively viewed photos of their dormmates ("targets"). Perceiver brain activity in regions associated with mentalizing and value computation differentiated between highly valued targets and other community members but did not differentiate between targets with middle versus low levels of social value. Crossvalidation analysis revealed that brain activity from novel perceivers could be used to accurately predict whether targets viewed by those perceivers were high in social value or not. These results held even after controlling for perceivers' own ratings of closeness to targets, and even though perceivers were not directed to focus on targets' social value. Overall, these findings demonstrate that individuals spontaneously monitor people identified as sources of strong connection in the broader community. social networks | social value | fMRI | prediction | mentalizing C ommunities allow people to cooperate and support each other, bolstering their collective and individual well-being. One key way in which groups maximize collective benefit is by rewarding prosocial individuals-for instance, through direct and indirect reciprocity. Such "social selection" is likely a crucial driver for the evolution of prosocial behaviors, and similar processes promote and sustain prosociality in economic games (1-6). Social selection, in turn, requires group members to first detect socially valuable peers, who are generous, trustworthy, and supportive to the community at large. In addition to benefiting the group, such detection can also aid individuals. Socially valuable others provide high-quality support and minimize others' stress (7-10). They also tend to be connected to other community members, and close relationships with them can offer a gateway to additional social resources (11, 12) . Despite the importance of social value detection, it remains unclear how capably people detect socially valuable others in dynamic, real-world communities, or the mechanisms through which this detection takes place. Here, we use a combination of social network analysis and neuroimaging to explore the possibility thateven absent explicit instructions to do so-individuals track their peers' social value. We focused on individuals undergoing the transition to college. During this period, individuals are separated from their previous social networks (i.e., family and high school friends) while facing increasing academic demands (13, 14) . They also rapidly build new communities, and students who quickly form close relationships on campus exhibit improved adjustment during the first year of college and beyond (15-18). We recruited newly matriculated college students from two freshman-only dormitories at Stanford University (n = 97) (12). In the second week of the academic year, we asked participants to nominate dorm members in response to eight prompts: for instance, identifying dorm members they viewed as socially supportive, positive, and empathic. We then identified "hubs" in each dorm: individuals who received unusually high numbers of nominations. In a second phase of the study, we scanned a subset of 50 students ("perceivers") using fMRI while they viewed photos of their fellow dorm members ("targets"). During this task, participants were not instructed to evaluate targets in any way. Nonetheless, we predicted that targets' social value would be reflected in perceivers' brain activity. Past work suggests that when individuals encounter popular individuals from their networks, they engage brain regions, including medial prefrontal cortex, temporoparietal junction, and ventral striatum (19, 20) . These regions are broadly associated with mentalizing-considering the internal states of other people-and with value computation. These regions are also preferentially engaged by salient social targets, such as ingroup members, suggesting that popular individuals likewise take on motivational relevance in social networks. Here, we build on that work in several ways. First, we controlled for perceivers' own relationship to each target when Significance To form successful communities, people must be able to detect socially valued individuals: people who are generous, supportive, and well-connected. Here, we provide evidence that people accomplish this detection by monitoring how the broader community views individuals. We used social network analysis to identify highly socially valued individuals in two college dormitories. We then scanned dorm residents using fMRI as they passively viewed pictures of dormmates. Activity in brain systems related to mentalizing and reward increased when people viewed highly valued, versus less valued, dormmates-even when controlling for individuals' own impressions of their dormmates. These data suggest that people robustly monitor peers' social value, potentially allowing them to efficiently locate high-quality social ties.