Money talks: neural substrate of modulation of fairness by monetary incentives.

Yun Wang,Liu-Qing Yang,Shu Li,Yuan Zhou,Li-Lin Rao

doi:10.3389/fnbeh.2014.00150

Abstract

A unique feature of the human species is compliance with social norms, e.g., fairness, even though this normative decision means curbing self-interest. However, sometimes people prefer to pursue wealth at the expense of moral goodness. Specifically, deviations from a fairness-related normative choice have been observed in the presence of a high monetary incentive. The neural mechanism underlying this deviation from the fairness-related normative choice has yet to be determined. In order to address this issue, using functional magnetic resonance imaging we employed an ultimatum game (UG) paradigm in which fairness and a proposed monetary amount were orthogonally varied. We found evidence for a significant modulation by the proposed amount on fairness in the right lateral prefrontal cortex (PFC) and the bilateral insular cortices. Additionally, the insular subregions showed dissociable modulation patterns. Inter-individual differences in the modulation effects in the left inferior frontal gyrus (IFG) accounted for inter-individual differences in the behavioral modulation effect as measured by the rejection rate, supporting the concept that the PFC plays a critical role in making fairness-related normative decisions in a social interaction condition. Our findings provide neural evidence for the modulation of fairness by monetary incentives as well as accounting for inter-individual differences.

Highlights

A unique feature of human beings is compliance with social norms even though this normative decision means curbing selfinterest (Buckholtz and Marois, 2012), which is another characteristic of human beings (Hobbes, 1994; Miller, 1999)
A post-hoc analysis revealed that the rejection rate for the unfair proposals with a high stake size was lower than that for the unfair proposals with a low stake size in the human condition (p = 0.012), whereas this difference only showed a trend toward significance in the computer condition (p = 0.062)
The computer condition provided us with an opportunity to investigate whether modulating the monetary incentive influences the perception of fairness only in a social interaction context

Summary

Introduction

A unique feature of human beings is compliance with social norms even though this normative decision means curbing selfinterest (Buckholtz and Marois, 2012), which is another characteristic of human beings (Hobbes, 1994; Miller, 1999). The ultimatum game (UG) nicely illustrates fairness, a salient, and elementary norm (Roth et al, 1991; Henrich, 2000), and provides a good paradigm for describing deviations from fairnessrelated normative choices In this game, two players have to agree on how to split a sum of money (stake). The unfair proposals are viewed as a violation of the fairness norm and the rejection of unfair proposals is, a normative decision (Buckholtz and Marois, 2012) During this decision process, the responders face two competing goals— a self-interest goal and a fairness goal. Implementation of this normative decision means that the responders succeed in curbing their self-interest goal, i.e., maximizing their economic gain by accepting the low offer, in order to pursue their fairness goal, i.e., punishing the proposer for the unfair offer by rejecting it

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Conclusion