其他摘要 | Fairness is one of the indispensable norms in human social life. The research on fairness decision-making behavior is an auxiliary agent to improve people's cooperative behavior in social life and to establish good interpersonal relationship. Neuroimaging studies suggest that the dorsolateral prefrontal cortex (DLPFC) plays an important role in fairness decision making, but there are still inconsistent findings. In this study, we first conducted a pre-experiment to verify the validity of the main effect and interaction effect of different fairness levels and proposer types in the ultimatum game (UG), which originates from the game theory in economics. We then used transcranial direct current stimulation (tDCS) to investigate the effect of different DLPFC stimulation modalities (left anode/right cathode, left cathode/right anode and sham stimulation) on responders' acceptance rates during the UG task. In addition, we also evaluated the subjects' judgment on fairness and their emotion assessed by the positive and negative affect scale (PANAS), aiming to study whether the tDCS in the brain region of DLPFC could affect the fairness judgment of the subjects or the positive and negative emotions of the subjects. Results: (1) the main effect of fairness levels and proposer types as well as the interaction effect on acceptance rate are significant in UG experimental paradigm. (2) during the UG task, there was no significant difference in the acceptance rate across different DLPFC stimulation modalities (left anode/right cathode, left cathode/right anode and sham stimulation) at each fair level (Ps > 0.05). However, after tDCS stimulation, the acceptance rate of the three stimulation groups was different when faced with different proposers (human or computer). Specifically, in the face of the extremely unfair distribution proposed by different proposers, the acceptance rate was significantly different in the left cathode/right anode group (P=0.006) and in the sham stimulation group (P= 0.032). That is, when the proposer was a human subject, the acceptance rate was lower, which suggested that the participants can discriminatively treat extremely unfair proposals from computer partners and human partners. However, there was no significant difference in the acceptance rate in the left anode/right cathode group (P=0.428), suggesting that these participants cannot discriminatively treat extremely unfair proposals from computer partners and human partners. Similarly, at the unfair level, the acceptance rate facing the human proposer was significantly lower than that of the computer proposer in the left cathode/right anode group (P=0.046). There was no significant difference in the acceptance rate between facing the human proposer and facing the computer proposer both in the sham stimulation group and the left anode/right cathode group (Ps>0.05). At the fairness level, there was no significant difference in the acceptance rate facing the human proposer and facing the computer proposer in each of the three groups (Ps>0.05). In addition, there were no significant differences in the response time across different DLPFC stimulation modalities (Ps>0.05). (3) there was a trend towards significance in the difference of fairness judgment on human or computer proposer across different DLPFC stimulation modalities (P=0.14). Specifically, no differences in fairness judgment on human or computer proposer in the sham group and the left anode/right cathode group, but the proposers from human partner was judged less unfair than those from computer group in the left cathode/right anode group. (4) There was no significant difference in positive or negative emotion across different DLPFC stimulation modalities (Ps > 0.05). Conclusion: We validated the effectiveness of the ultimatum game on investigating the effects of fairness and proposer type on responders’ acceptance rate. Using this UG task, we found that single-time tDCS stimulation on the DLPFC has no significant influence on the responders’ acceptance rate, but after receiving the left anode/right cathode tDCS participants could not discriminatively treat extremely unfair proposals from computer partners and human partners, unlike those participants receiving sham or the left cathode/right anode tDCS. This finding suggest the ability of the right DLPFC in integrating information and making decisions was depressed during the left anode/right cathode tDCS and thus further supports the unique role pf the right DLPFC in fairness decision making. Future studies can further clarify the role of the left or right DLPFC in fairness decision-making behavior, and further explore the neural mechanism of fairness decision-making behavior from the perspective of brain network by combining tDCS with functional magnetic resonance imaging. |
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