Behavioral and Neural Alterations in Competitive Behavior in Major Depressive Disorder

Background: The social defeat model of depression suggests individuals with depression are more likely to exhibit diminished competitive behavior within social contests. Here, we combine computational models of social behavior and functional neuroimaging to examine how valuation of social status and neural mechanisms of guilt contribute to alterations in competitive behavior among individuals with major depressive disorder (MDD). Method(s): Sixty-five participants with MDD (40 females, age: 34.7+/-11.2) and 47 matched non-psychiatric controls (30 females, age: 32.7+/-10.5) played a multi-round resource contest game with a computer opponent. In a given trial, a 'alpha' player first decided to transfer a portion of a monetary endowment to a 'beta' player. A social contest occurred if 'beta' decided to challenge, and the two players competed for the next round's alpha position. A hierarchical Bayesian model including two parameters of interest, i.e. guilt and preference for dominance, was fit to the observed behavioral choices. Result(s): Behaviorally, MDD participants made more highvalue transfers (p=.04) and challenged opponents as often as controls (p=0.48). Model estimation suggested higher guilt in MDD (p=.02), which positively correlated with depressive symptoms (p=.008), and comparable preference for dominance between the two groups (p=.68). Neurally, MDD participants showed intact striatal response to winning. Greater guilt was associated with transfer-associated activity in ventral medial prefrontal cortex and greater response of bilateral anterior insula to challenges. Conclusion(s): Enhanced guilt, combined with intact valuation of social status, suggests alterations in competitive behavior and associated neural mechanisms among depressive individuals may be attributable to a preference for equitable division of resources.