Abstract: The development of human society is inseparable from social norms, and the altruistic punishment is the key to maintain social norms. As an altruistic behavior, third-party punishment can maintain social norms, which is of great significance in promoting fairness and cooperation among people in the society. Third-party punishment occurs when people implement sanctioning mechanisms as an impartial bystander, the so called “third-party” refers to people who are not directly affected by others’ unfair behaviors. Third-party punishment decision-makings are also influenced by contexts. For example, there are some differences between third-party punishment decision-makings to maintain social fairness in the gain and loss contexts. In the loss context, the third-party has more willings to punish the perpetrator who violated social fairness. neuroimaging studies have identified several brain regions which related to the differences between gain and loss contexts in second-party altruistic punishment but the neural mechanisms for the differences in third-party altruistic punishment remain unsolved. According to previous studies, vmPFC is an important part of the mentalized brain network, and vmPFC is a brain region associated with reward processing, it is also able to assess people's intention of violating norms, primarily, vmPFC is associated with integrated emotions in third-party punishment. In this study, we applied the low-frequency repetitive transcranial magnetic stimulation (rTMS) to inhibit the function of bilateral ventromedial prefrontal cortex (vmPFC), and used the modified third-party punishment tasks to investigate the situations of third-party retributive punishment (Study 1) and the coexistence of third-party retributive punishment and third-party restorative punishment (Study 2) respectively. To further explore the role of vmPFC in third-party punishment decision-making, especially vmPFC in the differences of third-party punishment decision-making between the gain and loss contexts. The results of study 1 showed that, the function of the right vmPFC was inhibited by rTMS which accordingly reduced the third-party retributive punishment significantly in the loss context, but the same tendency did not found in the gain context, rTMS also inhibited the function of the left vmPFC, but the third-party retributive punishment decision-making did not make any changes in both the gain and loss contexts. In study 2, the results showed that the function of the right vmPFC was disrupted by rTMS which also reduced the third-party retributive punishment significantly in the loss context, but not in the gain context, specifically , the rate of third-party retributive punishment decreased more, and the rate of third-party restorative punishment wasunaffected . The brain function impairment of vmPFC significantly affected the third-party retributive punishment decision-makings for maintaining social fairness norms. Moreover, it was mainly caused by disrupting the function of right vmPFC, and the function of vmPFC also has the problem of lateralization in the third-party punishment decision-making. Summing up, this is the first study to provide the causal evidence that the vmPFC plays a pivotal role in modulating the differences between third-party punishment decision-making to maintain social fairness norms in the gain and loss contexts. Our results provide both theoretical and application values for the study of third-party punishment, and offer more supports for the research on the influence of contexts on people's altruistic punishment to maintain social fairness.

Key words: gain and loss contexts, third-party punishment, fairness norms, rTMS, vmPFC

摘要： 本研究应用低频rTMS技术，通过在第三方惩罚（研究1）及第三方惩罚和第三方补偿（恢复性惩罚）并存的情况下（研究2），对个体双侧vmPFC功能进行抑制，探索vmPFC在得失情境下第三方惩罚决策中的作用。研究1结果表明，rTMS抑制右侧vmPFC功能将降低损失情境下的第三方惩罚，收益情境下未发生改变。研究2得到与研究1一致的结果，且第三方惩罚减少程度更大，第三方补偿并未发生改变。这些结果强调了vmPFC与第三方惩罚紧密相关，在第三方判断得失情境的影响时起关键作用。

关键词: 得失情境, 第三方惩罚, 公平规范, 重复经颅磁刺激, 腹内侧前额叶皮层