451. Neural substrates of trust and social responsiveness in Veterans with posttraumatic stress symptoms

Abstract: Background: Many Veterans with posttraumatic stress disorder struggle with social dysfunction. However, the specific behavioral and neural substrates of social dysfunction remain unclear. Here, we use Veterans’ behavior in a social exchange task to evaluate two potential contributors to social dysfunction: diminished trust and social responsiveness. Methods: 165 combat Veterans completed ten rounds of an iterated Trust Game, including 161 undergoing functional magnetic resonance imaging. An additional group of 33 Veterans completed the task before and after residential PSTD treatment program. Trust was operationalized as the participant’s mean investment, and social responsiveness was operationalized as the relationship between investment change in response to partner reciprocation. Results: Higher posttraumatic stress symptoms (PTSS) were negatively correlated with trust (β=-0.0029, p < 0.005, n=161), and PTSS improvement after residential treatment was positively correlated with increases in trust (β=0.0078, p < 0.005, n=33). In contrast, subjects showed intact social responsiveness (β=0.126, p < 0.05, n=161) that was unrelated to PTSS (β< 0.001, p=0.81, n=161). Finally, ventral striatum activity in response repayment magnitude was negatively related to PTSS. Taken together, these data suggest diminished trust related to PTSS may be driven by an insensitivity to social reward among veterans. Conclusions: Together, our data indicate that diminished trust and an insensitivity to social rewards, rather than diminished social responsiveness, may underlie social dysfunction in Veterans with higher PTSS. This is consistent with prior literature finding intact reciprocity and impaired trust in civilians with PTSD and suggests that integrating attention to social anhedonia and interpersonal trust may enhance treatment outcomes for PTSS.