Abstract:  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 a 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 influence 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.

Key words: intention to help others, consequence, moral judgment, right temporo-parietal junction (RTPJ), transcranial direct current stimulation (tDCS)