公平行为的认知神经机制

大量研究采用最后通牒博弈发现人们愿意牺牲自身利益来维护公平，普遍具有不公平厌恶倾向。本文基于行为博弈任务对个体处于不同角色时的公平行为，从神经学层面做出新的解释，并对现存理论模型做了梳理。脑成像的研究发现，公平行为的相关脑区主要有负责情绪加工的脑岛和与认知控制相关的背外侧前额叶,内侧眶额皮层。前脑岛激活越大，个体拒绝不公平方案的可能性越大，而腹外侧前额叶可以调节前脑岛的活动，使个体采取更理性的方式，接受不公平分配方案。另外，睾酮素和催产素作为神经调节的激素，可以对公平行为起到调节作用，睾酮素通过抑制内侧眶额皮层的激活，增加对不公平方案的拒绝率，相反，催产素可以降低个体对于不公平方案的拒绝率，并增加个体的公平行为。

The Cognitive Neural Mechanism of Fairness

Given that we live in highly complex social environments, many of important decisions are made in the context of social interactions. A lot of studies have found that people are willing to sacrifice their own interests to maintain fair, which is called inequity aversion tendency. Simple but sophisticated tasks kown as UG（Ultimatum Game）have been used to study fairness in the laboratory setting , UG is a useful experimental tool for examining both decisions about, and responses to, fairness and equity . The Ultimatum Game (UG) is often used to examine responses to fairness. In the UG, two players must divide a sum of money, with the proposer specifying the division. The responder then has the option of accepting or rejecting this offer. If the offer is accepted, the sum is divided as proposed. If it is rejected, neither player receives anything. The UG therefore models decisions about resource allocation on the part of the proposer, as well as responses to fairness and inequity in the responder. The proposer’s decision is based on the degree of activation of VMPFC. VMPFC patients show “negative generosity” by offering less than they themselves demand，VMPFC is thought to be responsible for emotional processing and empathy，VMPFC patients can not understand unfair allocation will be rejected by responders. Moreover, unfair offers that were subsequently rejected were associated with a stronger insula response than those that were subsequently accepted, suggesting that the magnitude of anterior insula activation in?uences the decision to accept or reject. For different roles, the fairness behavior have different mechanism. For example, testosterone have different effects on different roles .It may have an similar effect on VMPFC function for proposers, Testosterone can increase individuals’ "negative generosity” behavior. On the other side, it also contributes to the individual refusal behavior for unfair distribution. In addition, a variety of neuroscience methods have been used to probe the underlying neural systems of fairness. This review highlights neural mechanisms of fairness, and describes existing theoretical models in detail. Although differences have been found in proposer and responder’s behavior, the fairness have some common basis. Brain imaging studies have found that the fairness was associated with activation in a network of regions including the insula which is responsible for the emotional processing and the dorsal medial prefrontal cortex which is responsible for cognitive control. As kind of neuromodulators, Oxytocin plays a catalytic role in social altruism behaviors such as fairness. It has been verified by many previous studies. This review point out some problems and the future research direction for the neural mechanisms of fairness.