Psychological asymmetry between punishment and reward in social dilemmas: Evidence from an fMRI study

Description: Sustaining group cooperation often requires individuals to sanction group members, either by punishing free-riders or rewarding cooperators. While these strategies can be structurally equivalent, humans typically show a behavioural reluctance to punish compared to reward. We propose that the decision to punish is distinguished from the decision to reward by a unique psychological barrier—the aversion to causing harm—that elicits greater motivational conflict. We tested this hypothesis using functional magnetic resonance imaging (fMRI) to measure neural activity during punishment and reward decisions in a novel adaptation of the Public Goods Game. Behaviourally, we found that severe non-cooperation was punished less often than its cooperative equivalent was rewarded. Neurally, we found that deciding on punishment elicited robustly greater activity in the dorsal anterior cingulate cortex (dACC)—a region central to conflict monitoring—than deciding on reward. This asymmetry was specific to the dACC and was not observed in the dorsolateral prefrontal cortex (DLPFC), a region typically associated with resolving conflict. These results identify a neural signature for the psychological asymmetry between punishment and reward in social dilemmas, demonstrating that punishing non-cooperation imposes a greater burden of motivational conflict than rewarding cooperation.