The mentalizing network orchestrates the impact of parochial altruism on social norm enforcement

Abstract

Parochial altruism-a preference for altruistic behavior towards ingroup members and mistrust or hostility towards outgroup members-is a pervasive feature in human society and strongly shapes the enforcement of social norms. Since the uniqueness of human society critically depends on the enforcement of norms, the understanding of the neural circuitry of the impact of parochial altruism on social norm enforcement is key, but unexplored. To fill this gap, we measured brain activity with functional magnetic resonance imaging (fMRI) while subjects had the opportunity to punish ingroup members and outgroup members for violating social norms. Findings revealed that subjects' strong punishment of defecting outgroup members is associated with increased activity in a functionally connected network involved in sanction-related decisions (right orbitofrontal gyrus, right lateral prefrontal cortex, right dorsal caudatus). Moreover, the stronger the connectivity in this network, the more outgroup members are punished. In contrast, the much weaker punishment of ingroup members who committed the very same norm violation is associated with increased activity and connectivity in the mentalizing-network (dorsomedial prefrontal cortex, bilateral temporo-parietal junction), as if subjects tried to understand or justify ingroup members' behavior. Finally, connectivity analyses between the two networks suggest that the mentalizing-network modulates punishment by affecting the activity in the right orbitofrontal gyrus and right lateral prefrontal cortex, notably in the same areas showing enhanced activity and connectivity whenever third-parties strongly punished defecting outgroup members.

Dorsolateral and ventromedial prefrontal cortex orchestrate normative choice

“…The same argument holds for the observed activation in the dorsomedial prefrontal cortex (dMPFC, BA 10; Supplementary Fig. 2b), which has been implicated in mind-reading tasks in numerous studies 12,38,39 . Subjects in the right and left TMS group showed no differential activation in these areas, suggesting that this brain region is equally capable of processing the reading of intentions behind unfair offers in both treatment groups.…”

“…Studies on such subjects also have limited opportunities for experimental manipulations, and there is the possibility of functional reorganization after brain lesions, rendering the interpretation of behavioral differences in terms of neural characteristics difficult. To overcome these limits, recent studies used brain imaging methods [7][8][9][10][11][12][13][14][15] and brain stimulation methods [16][17][18] to investigate the neural mechanisms behind normative decisions.…”

The neurobiology of rewards and values in social decision making

“…The (un) fairness of choices resulting in outcome distributions is therefore encoded in neural structures that overlap with those often presumed to encode anticipated values of non-social choices (which is in accordance with the extended common currency schema). However, in close similarity to the effects of vicarious reward experience (discussed above), fairness-related neural responses and the associated behaviour can strongly depend on contextual factors, such as the proposer's intentions 92 , the relation of a specific offer's distribution to the average in a series of offers 93 or whether the opponent belongs to the player's social group or a rival group 96 . This contradicts a direct, automatic mapping of the objective 'fairness' of others' decisions to neural responses in the reward system and raises questions about the origins of these value-related responses.…”

“…This contradicts a direct, automatic mapping of the objective 'fairness' of others' decisions to neural responses in the reward system and raises questions about the origins of these value-related responses. One possible mechanism by which social principles may influence value-coding regions is through functional connectivity with areas involved in social cognition (such as the TPJ and dmPFC 96 ), as has been observed for basic social reward experience 38 and for altruistic 45 and vicarious 69 choices. Valuation-related neural brain structures may also be implicated in abstract social decisions that do not involve any personal gains or losses for the participant.…”

Group bias in cooperative norm enforcement

“…People were more likely to cooperate with members of their own group, and, as in Bernhard et al, third parties were more likely to punish when an in-group member had been the victim of defection, showing that this finding holds across different economic contexts and group manipulations. Still other studies have shown that third parties are particularly protective of in-group victims when norm violations are committed by out-group members [22,49,50].…”