Diminishing Reciprocal Fairness by Disrupting the Right Prefrontal Cortex

Abstract

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.

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

“…We report results in a priori regions of interests (previously defined in neuroimaging studies on punishment [Buckholtz et al, 2008;de Quervain et al, 2004;Knoch et al, 2006;Sanfey et al, 2003;Spitzer et al, 2007;Strobel et al, 2011] and mentalizing [Van Overwalle 2009]): OFG, right lateral PFC, caudatus, DMPFC, TPJ where activations are significant at P < 0.005 uncorrected for multiple comparisons with an extent threshold of 10 voxels [Lieberman and Cunningham, 2009], and survive small volume corrections (SVC) for multiple comparisons (or family-wise error [FWE] corrections across the whole brain). The SVC procedure, as implemented in SPM5 using the FWE correction procedure (P < 0.05), allows results to be corrected for multiple nonindependent comparisons with a defined region of interest.…”

“…For the punishment-related activated in the rLPFC, we averaged the peak coordinates of a second-party norm enforcement study (x ¼ 40, y ¼ 36, z ¼ 22) [Sanfey et al, 2003] where disruption by rTMS [Knoch et al, 2006] or tDCS [Knoch et al, 2008] reduces subject's ability to control their economic self-interest. Activations in other regions were only considered significant if they survived whole-brain FWE correction for multiple comparisons at P < 0.05 (in line with established procedures [Frackowiak et al, 2004]), but are reported for completeness at a threshold of P < 0.005 uncorrected for multiple comparisons.…”

“…Although recent studies have fundamentally improved our knowledge of how the brain modulates norm compliance [Baumgartner et al, 2008[Baumgartner et al, , 2009Delgado et al, 2005;Harbaugh et al, 2007;King-Casas et al, 2005;Rilling et al, 2002;Spitzer et al, 2007] and norm enforcement [Buckholtz et al, 2008;de Quervain et al, 2004;Fehr and Camerer, 2007;Knoch et al, 2006Knoch et al, , 2008Rangel et al, 2008;Sanfey, 2007;Sanfey et al, 2003;Strobel et al, 2011] they do not examine the parochial nature of this phenomena. There is also an important literature examining the neural circuitry of the cognitions involved in the evaluation of faces from distinct races [Cunningham et al, 2004;Golby et al, 2001;Phelps et al, 2000], the judgment of people belonging to other races [Eberhardt, 2005;Freeman et al, 2010;Ito and Bartholow, 2009;Lieberman et al, 2005;Richeson et al, 2003], prejudice [Beer et al, 2008], the evaluation of very poor and ''disgusting'' outgroups such as addicts and beggars in dirty clothes [Harris and Fiske, 2006], and the general evaluation of ingroup-outgroup interactions [Mathur et al, 2010;Van Bavel et al, 2008] but none of the individuals in these studies had to make costly punishment decisions that involved real costs and benefits for themselves or for others.…”

“…Recent neuroimaging studies on second-party norm enforcement suggest that two brain regions in particular play a decisive and functionally distinctive role in punishment-related decision processes; these are the right lateral PFC [Knoch et al, 2006[Knoch et al, , 2008Sanfey et al, 2003] and the dorsal caudatus [de Quervain et al, 2004;Seymour et al, 2007]. Evidence from transcranial magnetic stimulation (TMS) [Knoch et al, 2006;van 't Wout et al, 2005] and transcranial direct current stimulation (tDCS) [Knoch et al, 2008] studies suggests that the right lateral PFC is causally involved in (costly) norm enforcement behavior by modulating the weight of self-interest in the decision process.…”

“…Evidence from transcranial magnetic stimulation (TMS) [Knoch et al, 2006;van 't Wout et al, 2005] and transcranial direct current stimulation (tDCS) [Knoch et al, 2008] studies suggests that the right lateral PFC is causally involved in (costly) norm enforcement behavior by modulating the weight of self-interest in the decision process. On the other hand, punishment-related activity in the dorsal caudatus (a brain region strongly implicated in the processing of rewards that accrue as a result of goaldirected actions [Fliessbach et al, 2007;Kawagoe et al, 1998;O'Doherty et al, 2004;Schultz and Romo, 1988]) in combination with behavioral and questionnaire measures suggests that people derive satisfaction from punishing norm violators [de Quervain et al, 2004;Singer et al, 2006].…”