Be nice if you have to -- the neurobiological roots of strategic fairness (original) (raw)
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Diminishing Reciprocal Fairness by Disrupting the Right Prefrontal Cortex
Science, 2006
Humans restrain self-interest with moral and social values. They are the only species known to exhibit reciprocal fairness, which implies the punishment of other individuals' unfair behaviors, even if it hurts the punisher's economic self-interest. Reciprocal fairness has been demonstrated in the Ultimatum Game, where players often reject their bargaining partner's unfair offers. Despite progress in recent years, however, little is known about how the human brain limits the impact of selfish motives and implements fair behavior. Here we show that disruption of the right, but not the left, dorsolateral prefrontal cortex (DLPFC) by low-frequency repetitive transcranial magnetic stimulation substantially reduces subjects' willingness to reject their partners' intentionally unfair offers, which suggests that subjects are less able to resist the economic temptation to accept these offers. Importantly, however, subjects still judge such offers as very unfair, which indicates that the right DLPFC plays a key role in the implementation of fairness-related behaviors.
Manipulation of Pro-Sociality and Rule-Following with Non-invasive Brain Stimulation
Decisions are often governed by rules on adequate social behaviour. Recent research suggests that the right lateral prefrontal cortex (rLPFC) is involved in the implementation of internal fairness rules (norms), by controlling the impulse to act selfishly. A drawback of these studies is that the assumed norms and impulses have to be deduced from behaviour and that norm-following and pro-sociality are indistinguishable. Here, we directly confronted participants with a rule that demanded to make advantageous or disadvantageous monetary allocations for themselves or another person. To disentangle its functional role in rule-following and pro-sociality, we divergently manipulated the rLPFC by applying cathodal or anodal transcranial direct current stimulation (tDCS). Cathodal tDCS increased participants’ rule-following, even of rules that demanded to lose money or hurt another person financially. In contrast, anodal tDCS led participants to specifically violate more often those rules that were at odds with what participants chose freely. Brain stimulation over the rLPFC thus did not simply increase or decrease selfishness. Instead, by disentangling rule-following and pro-sociality, our results point to a broader role of the rLPFC in integrating the costs and benefits of rules in order to align decisions with internal goals, ultimately enabling to flexibly adapt social behaviour.
Inequality signals in dorsolateral prefrontal cortex inform social preference models
Social cognitive and affective neuroscience, 2018
Humans typically display inequality aversion in social situations, which manifests itself as a preference for fairer distributions of resources. However, people differ in the degree to which they dislike being worse off [disadvantageous inequality (DI) aversion] or better off [advantageous inequality (AI) aversion] than others. Competing models explain such behavior by focusing on aversion to payoff differences, maximization of total payoff or reciprocity. Using functional near-infrared spectroscopy, we asked which of these theories could better explain dorsolateral prefrontal cortex (dlPFC) activity while participants accepted or punished fair vs unfair monetary transfers in an anonymous norm compliance task. We found that while all participants exhibited DI aversion, there were substantial differences in preferences for AI, which were strongly predicted by dlPFC activation. Model comparisons revealed that both punishment behavior and prefrontal activity were best explained by a mo...
Increasing generosity by disrupting prefrontal cortex
Social Neuroscience, 2016
Recent research suggests that prosocial outcomes in sharing games arise from prefrontal control of self-maximizing impulses. We used continuous Theta Burst Stimulation (cTBS) to disrupt the functioning of two prefrontal areas, the right dorsolateral prefrontal cortex (DLPFC) and dorsomedial prefrontal cortex (DMPFC). We used cTBS in the right MT/V5, as a control area. We then tested subjects' prosocial inclinations with an unsupervised Dictator Game in which they allocated real money anonymously between themselves and low and high socioeconomic status (SES) players. cTBS over the two prefrontal sites made subjects more generous compared to MT/V5. More specifically, cTBS over DLPFC increased offers to high SES players, while cTBS over DMPFC caused increased offers to low SES players. These data, the first to demonstrate an effect of disruptive neuromodulation on costly sharing, suggest that DLPFC and MPFC exert inhibitory control over prosocial inclinations during costly sharing, though they may do so in different ways. DLPFC may implement contextual control, while DMPFC may implement a tonic form of control. This study demonstrates that humans' prepotent inclination is toward prosocial outcomes when cognitive control is reduced, even when prosocial decisions carry no strategic benefit and concerns for reputation are minimized.
The prefrontal cortex and (uniquely) human cooperation: a comparative perspective
Neuropsychopharmacology, 2021
Humans have an exceptional ability to cooperate relative to many other species. We review the neural mechanisms supporting human cooperation, focusing on the prefrontal cortex. One key feature of human social life is the prevalence of cooperative norms that guide social behavior and prescribe punishment for noncompliance. Taking a comparative approach, we consider shared and unique aspects of cooperative behaviors in humans relative to nonhuman primates, as well as divergences in brain structure that might support uniquely human aspects of cooperation. We highlight a medial prefrontal network common to nonhuman primates and humans supporting a foundational process in cooperative decision-making: valuing outcomes for oneself and others. This medial prefrontal network interacts with lateral prefrontal areas that are thought to represent cooperative norms and modulate value representations to guide behavior appropriate to the local social context. Finally, we propose that more recently...
Unfair? It depends: neural correlates of fairness in social context
Social cognitive and affective neuroscience, 2010
Fairness is a key concept in social interactions and is influenced by intentionality considerations. In this functional magnetic resonance imaging study, we investigated the neural correlates of fairness by focusing on responder behavior to unfair offers in an Ultimatum Game paradigm with conditions that differed in their intentionality constraints. Brain activity underlying rejection vs acceptance of unfair offers appeared highly dependent on intentionality. Rejection of unfair offers when the proposer had no-alternative as well as acceptance of offers when the proposer had a fair- or hyperfair-alternative was associated with activation in a network of regions including the insula and the dorsal medial prefrontal cortex. These activations were interpreted as neural responses to norm violations because they were mostly involved when behavior was inconsistent with socially accepted behavior patterns. Rejection of unfair offers in the no-alternative condition further resulted in activ...
The Neural Basis of Egalitarian Behavior
Proceedings of the National Academy of Science, 2012
Individuals are willing to sacrifice their own resources to promote equality in groups. These costly choices promote equality and are associated with behavior that supports cooperation in humans, but little is known about the brain processes involved. We use functional MRI to study egalitarian preferences based on behavior observed in the “random income game.” In this game, subjects decide whether to pay a cost to alter group members’ randomly allocated incomes.Wespecifically examinewhether egalitarian behavior is associated with neural activity in the ventromedial prefrontal cortex and the insular cortex, two regions that have been shown to be related to social preferences. Consistent with previous studies, we find significant activation in both regions; however, only the insular cortex activations are significantly associated with measures of revealed and expressed egalitarian preferences elicited outside the scanner. These results are consistent with the notion that brain mechanisms involved in experiencing the emotional states of others underlie egalitarian behavior in humans.
NeuroImage, 2011
In this functional magnetic resonance imaging study, we examined developmental changes in the brain regions involved in reactions to unfair allocations. Previous studies on adults suggested that reactions to unfairness are not only affected by the distribution itself but also by the ascribed intentionality of the proposer. In the current study, we employed the mini Ultimatum Game (Falk, Fehr, & Fischbacher, 2003) to examine responder behavior to unfair offers of varying degrees of intentionality. Sixty-eight participants from four age groups (10-, 13-, 15-, and 20-year-olds) carried out the task while fMRI data were acquired. Participants of all ages showed activation in the bilateral insula and dorsal anterior cingulate cortex (dACC) during rejection of unintentional but acceptance of intentional unfair offers. Rejection of unintentional unfair offers further involved increasing activation with age in the temporoparietal junction and the dorsolateral prefrontal cortex. These findin...
Behavioural Differences and Neural Substrates of Altruistic and Spiteful Punishment
Scientific reports, 2017
Altruistic punishment following social norm violations promotes human cooperation. However, experimental evidence indicates that some forms of punishment are spiteful rather than altruistic. Using two types of punishment games and seven non-strategic games, we identified strong behavioural differences between altruistic and spiteful punishers. Altruistic punishers who rejected unfair offers in the ultimatum game and punished norm violators in the third-party punishment game behaved pro-socially in various non-strategic games. Spiteful punishers who rejected unfair offers in the ultimatum game but did not punish norm violators in the third-party punishment game behaved selfishly in non-strategic games. In addition, the left caudate nucleus was larger in spiteful punishers than in altruistic punishers. These findings are in contrast to the previous assumption that altruistic punishers derive pleasure from enforcement of fairness norms, and suggest that spiteful punishers derive pleasu...
NeuroImage, 2012
Everything else being the same, an equal outcome is generally preferred; however, an equitable allocation sometimes is possible only by sacrificing the total amount of resources available to society. Moreover, direct interests may interact with the perception of equality. Here, we have investigated individual preferences, and their neural basis, by employing a task in which an allocation of a fixed amount between the subject and another person (MS condition) or two third parties (TP condition) is randomly determined. The subject can accept or reject the outcome, in the same fashion as the Ultimatum Game: thus an unequal offer may be rejected at the cost of a loss in total amount. Behavioral results show preference for equal outcomes in TP and for equal and advantageous outcomes in MS. An activation of medial prefrontal cortex (mPFC), extending to the anterior middle cingulate cortex (aMCC), was found in MS unequal outcomes, particularly for disadvantageous outcomes and consequent rejections. The anterior insula (AI) was active for unequal outcomes, in both MS and TP. We propose that the equal treatment is a default social norm, and its violation is signaled by the AI, whereas aMCC/mPFC activation, negatively correlated to rejections, reflects the effort to overcome the default rule of equal treatment in favor of a self-advantageous efficiency.► We manipulate equality and self-interest of the offer in a modified Ultimatum Game. ► Participants reject unequal and self-disadvantageous offers. ► Anterior insula signals inequality, independently of self-interest. ► Inequality is interpreted as a violation of expected outcome. ► Medial prefrontal cortex processes self-interested motivations.