Serotonin and Aversive Processing in Social and Nonsocial Contexts

Abstract

Background Decades of research have linked serotonin (5-HT) to prosocial behavior across species; however, the specific mechanisms mediating this relationship have not yet been elucidated. We examine the influence of 5-HT on prosocial behavior by considering its function in basic motivational processes. Influential theories have implicated 5-HT in impulsivity, aversive processing, and behavioral inhibition. Design In a series of behavioral experiments performed in humans, we showed that 5-HT is critical for behavioral inhibition in the face of aversive predictions, but not overall motor response inhibition or sensitivity to aversive outcomes. We further investigated how 5-HT shapes prosocial behavior by examining its influence on costly punishment, the willingness to incur personal costs to punish social norm violations. Several studies have shown that costly punishment of cheaters promotes group cooperation, suggesting that costly punishment is a prosocial act. However, costly punishment can be driven by prosocial fairness concerns, or by antisocial retributive motives. Results 5-HT manipulations had bi-directional effects on costly punishment behavior; enhancing 5-HT function with citalopram reduced costly punishment, whereas depleting the 5-HT precursor tryptophan enhanced costly punishment. Neural and behavioral evidence suggested that 5-HT shapes punishment behavior by regulating retributive motives. Conclusion For our understanding of 5-HT in healthy and disordered cognitive and affective processing the implications of these findings are discussed.