经颅直流电刺激右侧颞顶联合区对助人意图加工的影响

Cathodal transcranial direct current stimulation on the right temporo-parietal junction modulates the helpful intention processing

对意图信息的理解是影响道德判断的重要因素,已有研究证实在伤人行为道德判断中,右侧颞顶联合区与意图加工具有因果关联,而在助人行为道德判断中,意图加工的作用及其关键脑区还不清楚。本研究采用经颅直流电刺激技术阴极刺激右侧颞顶联合区,考察抑制该脑区的活动对被试在道德判断中对助人意图信息加工的影响。结果发现在助人行为道德判断中,个体对正性助人意图的赞扬度评价显著高于中性意图,对正性结果的赞扬度评价显著高于中性结果,二者没有交互作用;且只在正性意图条件下,阴极刺激被试右侧颞顶联合区后,其做出道德判断的反应时显著缩短。该结果揭示了右侧颞顶联合区在助人意图加工中的核心作用,抑制该脑区的激活能影响个体在道德判断中对助人意图的加工。

Helping behaviors are critically important for human social development. However, most moral neuroscience studies have concentrated on immoral and negative behaviors such as killing, murder and harm. The neural mechanism of helpful intention processing in moral judgment is still unclear. Functional MRI studies have demonstrated the involvement of the right temporo-parietal junction （RTPJ） in the attribution of mental states. Previous studies have found that the role of intention processing in harmful moral judgment can be modulated by changing the cortical excitability of RTPJ with transcranial direct current stimulation （tDCS）. Will the RTPJ play a critical role in the intention processing during moral judgment of helpful behavior？ In order to explore the potential causal role of RTPJ in helpful moral judgement, the present study manipulates the cortical excitability of RTPJ with cathodal tDCS. We hypothesize that inhibiting the neural activity of RTPJ with cathodal tDCS could influence the role of intention processing in helpful moral judgment. To test the hypothesis, 18 healthy right-handed adults participated in this study. All participants underwent both cathodal and sham tDCS sessions in random order. Participants were counter-balanced in 2 separate days with a 1 week interval between both stimulations. To assure the target cortex to be activated completely, a relatively weak current （1.5 mA） was constantly delivered over the RTPJ for 20 min. For the sham tDCS, the stimulation only lasted for 15 sec. After stimulation, participants read stories in a 2 （intention： positive vs. neutral） ×2 （outcome： positive vs. neutral） design and were asked to make moral judgment about how much praise the actor deserves. We analyzed the praise score and reaction time by × 2 （intention）× 2 （outcome） ×2 （tDCS： cathodal, sham） repeated measures ANOVA. Results showed that actors with positive intentions were judged more praiseworthy than those with neutral intentions, and actors producing positive outcomes were judged more praiseworthy than those causing neutral outcomes. However, there was no significant interaction between intention and outcome. For the reaction time, judgments of positive intentions were faster than that of neutral intentions. The responses to positive outcomes were faster than neutral outcomes. Most importantly, the moral judgments were faster under cathodal tDCS than sham tDCS stimulation, especially under the positive intention condition rather than the neutral intention condition. The present study assessed the potential effect of the tDCS on helpful intention processing in moral judgment. Our findings indicate that the response times of moral judgment in the positive intention condition were shorten after receiving the cathodal stimulation, suggesting that altering the cortical excitability in the RTPJ could infiuenc＇e human＇s socio-cognitive ability. These results demonstrate the critical role of RTPJ in intention processing during helpful moral judgment, which provides us a better understanding about the role of RTPJ in moral judgment and helping behaviors.