Ignacio Sáez, Lusha Zhu, Eric Set, Andrew Kayser, Ming Hsu

Highlights

• Dopamine is causally associated with human prosocial behavior;

• Pharmacological dopamine enhancement led to prioritizing of egalitarian motives;

• Computational modeling of inequity aversion captures drug-induced changes;

• Results support involvement of dopamine in computing prosocial valuation signal;

Summary Egalitarian motives form a powerful force in promoting prosocial behavior and enabling large-scale cooperation in the human species [ 1 ]. At the neural level, there is substantial, albeit correlational, evidence suggesting a link between dopamine and such behavior [ 2, 3 ].

However, important questions remain about the specific role of dopamine in setting or modulating behavioral sensitivity to prosocial concerns. Here, using a combination of pharmacological tools and economic games, we provide critical evidence for a causal involvement of dopamine in human egalitarian tendencies. Specifically, using the brain penetrant catechol-O-methyl transferase (COMT) inhibitor tolcapone [ 4, 5 ], we investigated the causal relationship between dopaminergic mechanisms and two prosocial concerns at the core of a number of widely used economic games: (1) the extent to which individuals directly value the material payoffs of others, i.e., generosity, and (2) the extent to which they are averse to differences between their own payoffs and those of others, i.e., inequity. We found that dopaminergic augmentation via COMT inhibition increased egalitarian tendencies in participants who played an extended version of the dictator game [ 6 ].

Strikingly, computational modeling of choice behavior [ 7 ] revealed that tolcapone exerted selective effects on inequity aversion, and not on other computational components such as the extent to which individuals directly value the material payoffs of others. Together, these data shed light on the causal relationship between neurochemical systems and human prosocial behavior and have potential implications for our understanding of the complex array of social impairments accompanying neuropsychiatric disorders involving dopaminergic dysregulation. Received: September 17, 2014;

Received in revised form: December 15, 2014; Accepted: January 30, 2015; Published Online: March 19, 2015 © 2015 Elsevier Ltd. Published by Elsevier Inc. All rights reserved.