PROJECT SUMMARY - Nearly half of the U.S. population sometimes or always experiences loneliness. This is alarming, in part, because loneliness confers risk for negative mental and physical health outcomes. Extensive research suggests loneliness is characterized by subjective isolation: many lonely individuals maintain a number of relationships but still report feeling lonely. Thus, a neurobiological account of loneliness requires that we understand how the brain represents our subjective connections to others and how loneliness alters these representations. The long-term goal of this proposal is to identify how subjective isolation is represented in the brain in order to identify novel ways to intervene on this representation to attenuate loneliness. We propose that medial prefrontal cortex (MPFC) and posterior cingulate (PC), which comprise a functional network in the brain, organize our representations of people based on our subjective connection to them and that loneliness systematically alters this organization. In Specific Aim 1, we will determine whether subjective closeness organizes self and other representations in MPFC/PC. While undergoing fMRI, participants will complete tasks in which they reflect on their own and other people’s personalities and mental states. They will also report on their subjective closeness, similarity, and familiarity to the other people. Representational similarity analysis (RSA) will test 1) whether the brain organizes mental representations of the self and one’s own social network members based on subjective closeness and 2) whether the subjective closeness model better explains the organization of self and other representations than the alternative possibilities of perceived similarity, familiarity, or trait-dimensions. In Specific Aim 2, we will determine how loneliness modulates self and other representations in MPFC/PC. We predict that trait loneliness corresponds with MPFC/PC patterns reflecting 1) greater differentiation between self and others and/or 2) less differentiation between close others and acquaintances. Individual difference measures that are related, but non-redundant, with loneliness (i.e., self-esteem, depression) will also be collected to isolate the specificity of our findings to loneliness. In Specific, Exploratory Aim 3, we will determine the cognitive consequences of altered self and other representation in loneliness. Participants will also complete fMRI tasks designed to test novel hypotheses generated by our pilot data regarding the neurocognitive processes altered by loneliness. Participants will be asked to judge the interpersonal closeness and similarity in personalities between self and social network members. We predict that loneliness will be associated with exaggerating the difference between self and other personalities while also overgeneralizing the similarity of other people’s personalities, both of which will be underpinned by aberrant responses in MPFC, given its role ...