Psychology Department, Rutgers University, Newark, New Jersey 07102, USA.
Nature. 2010 Feb 25;463(7284):1089-91. doi: 10.1038/nature08785.
A popular hypothesis in the social sciences is that humans have social preferences to reduce inequality in outcome distributions because it has a negative impact on their experienced reward. Although there is a large body of behavioural and anthropological evidence consistent with the predictions of these theories, there is no direct neural evidence for the existence of inequality-averse preferences. Such evidence would be especially useful because some behaviours that are consistent with a dislike for unequal outcomes could also be explained by concerns for social image or reciprocity, which do not require a direct aversion towards inequality. Here we use functional MRI to test directly for the existence of inequality-averse social preferences in the human brain. Inequality was created by recruiting pairs of subjects and giving one of them a large monetary endowment. While both subjects evaluated further monetary transfers from the experimenter to themselves and to the other participant, we measured neural responses in the ventral striatum and ventromedial prefrontal cortex, two areas that have been shown to be involved in the valuation of monetary and primary rewards in both social and non-social contexts. Consistent with inequality-averse models of social preferences, we find that activity in these areas was more responsive to transfers to others than to self in the 'high-pay' subject, whereas the activity of the 'low-pay' subject showed the opposite pattern. These results provide direct evidence for the validity of this class of models, and also show that the brain's reward circuitry is sensitive to both advantageous and disadvantageous inequality.
在社会科学中，有一种流行的假说认为，人类具有减少结果分配不平等的社会偏好，因为这会对他们所体验到的奖励产生负面影响。尽管有大量的行为和人类学证据与这些理论的预测一致，但没有直接的神经证据表明存在厌恶不平等的偏好。这种证据将特别有用，因为一些与不平等结果不相关的行为也可以用对社会形象或互惠的关注来解释，而这些并不需要对不平等的直接厌恶。在这里，我们使用功能磁共振成像直接测试人类大脑中是否存在厌恶不平等的社会偏好。通过招募一对受试者并给予其中一人大量的货币津贴来创造不平等。当两个受试者都评估实验者对自己和另一个参与者的进一步货币转移时，我们测量了腹侧纹状体和腹内侧前额叶皮层的神经反应，这两个区域在社会和非社会环境中都被证明与货币和主要奖励的评估有关。与厌恶不平等的社会偏好模型一致，我们发现这些区域的活动对“高报酬”受试者向他人的转移比对自己的转移更敏感，而“低报酬”受试者的活动则呈现相反的模式。这些结果为这类模型的有效性提供了直接证据，也表明大脑的奖励回路对有利和不利的不平等都很敏感。
