Blain, Scott2021-10-132021-10-132021-08https://hdl.handle.net/11299/225016University of Minnesota Ph.D. dissertation. 2021. Major: Psychology. Advisors: Colin DeYoung, Robert Krueger. 1 computer file (PDF); xiii, 251 pages.Though humans are universally social, we vary considerably in our ability and motivation to form and maintain relationships. One approach to explaining this variation looks to identify the mechanisms that facilitate social behavior, including social cognition and reward sensitivity. Much of this work, however, is methodologically lacking and fails to provide comprehensive explanatory frameworks. This dissertation applies insights from personality psychology to improve our understanding of individual differences in social cognition and interpersonal functioning, focusing on the broad traits most descriptive of social behavior: Agreeableness, Extraversion, and Trait Affiliation. Across four studies attempting to elucidate the neurocognitive mechanisms of these traits, various methods—including questionnaires, behavioral tasks, fMRI, and psychometric techniques—were used to elucidate how and why individuals vary in their social abilities, behaviors, and associated outcomes. Study 1 was a multi-task investigation of how three Agreeableness-Antagonism subfactors differentially predict social cognitive ability. Study 2 used fMRI, along with personality questionnaires and behavioral tasks, to examine associations among Agreeableness, social cognitive ability, and function of the brain’s default network, applying structural equation modeling and a Bayesian individualized cortical parcellation approach. Study 3 failed to replicate classic associations demonstrated between measures of depressivity and reward sensitivity, suggesting that instead, reward sensitivity is related primarily to Extraversion. Finally, Study 4 explored Trait Affiliation, an important dimension at the intersection of Agreeableness and Extraversion, and presents a new Trait Affiliation Scale, along with evidence for its reliability, validity, and practical utility. Collectively, this work represents a high standard of statistical power and methodological rigor, utilizing a total of eight independent samples ranging from N = 195 to N = 25,732. Across these studies, social cognitive ability and reward sensitivity are further established as important psychological mechanisms underlying individual differences in social functioning. The work presented here also offers methodological contributions and broader theoretical insights into the understanding of personality and its relation to psychopathology. In sum, this dissertation paves the way to a better understanding of how and why individuals vary in our social abilities, interpersonal interactions, and relationship success, in addition to serving as an argument for the broad utility of personality psychology’s methods and theories.enfMRIPersonalityPsychopathologyRelationshipsSocial BehaviorSocial CognitionThesis or Dissertation