第三方惩罚的神经机制：来自经颅直流电刺激的证据

" It has been widely recognized that the social order of human societies is largely maintained by social norms. However, we still know little about the cognitive and emotional foundations which shape social norms, making it hard (if not impossible) to understand how social norms are generated and maintained. Prior neural studies, which mainly perform second-party punishment based on the ultimatum framework, rarely explore the relevant brain areas as well as the neural mechanisms of third-party punishment driven by social norms. In the current study, we try to provide evidences which support that two types of mechanisms (i.e., negative emotions and self-interest mechanisms) influence social norms compliance of third-parties with opposite directions. Meanwhile, right dorsolateral prefrontal area (DLPFC) plays a crucial role in this process.In this study, we used transcranial direct current stimulation (tDCS) to investigate whether effects of increased or decreased right DLPFC excitability influenced third-party punishment in a dictator game. Following an experimental design of between-subject (tDCS treatments: anodal, cathodal, sham) within-subject (cost of punishment treatments: without cost, with cost), ninety participants were first randomly assigned to receive either anodal, cathodal, or sham stimulation of 15 min, then they performed two dictator game tasks as third-parties. In Task (without cost) participants did not need to bear any costs for their punishments (none cost task), while in Task (with cost) they were required to pay for their punishment actions.The results are given as follows. We first performed repeated measured ANOVA and one-way ANOVA to examine the effect of tDCS stimulation treatments (anodal, cathodal and sham) on emotion response. We found significant main effects of tDCS on the emotion response. Meanwhile, post hoc analysis (SNK) showed that the anodal stimulation decreased the negative emotions while the cathodal stimulation enhanced the negative emotions. Second, results of repeated measured ANOVA and one-way ANOVA showed significant main effects of tDCS on punishments in the none cost Task , and post hoc analysis (SNK) showed that the cathodal stimulation significantly increased punishments while the results of anodal stimulation were insignificant. Third, We also conducted repeated measured ANOVA and one-way ANOVA to test whether the difference of punishments between two tasks differed in tDCS groups, and found main effects of tDCS were significant. Moreover, post hoc analysis (SNK) showed that the difference of punishments between two tasks was significantly higher in the cathodal stimulation than that in the sham stimulation, while the results of anodal stimulation were insignificant compared to that in the sham stimulation.The present study provides one of the first neural evidences for the role of right DLPFC in third-parties social norm compliance, and supports mechanism explanations of negative emotions and self-interest. The outcomes indicate that DLPFC, by affecting the processes of negative emotions and self-interest, is an important brain area of social norm compliance. When third-parties are confronted with violations of social norms, their brain first releases negative emotions, which drives third-parties to punish violators. Further, if third-parties need to pay for their compliance with social norms, their rational goals about self-interest will weaken negative emotional impulses, and finally make their compliance with social norms depends on the trade-offs between negative emotions and self-interest mechanisms. "