Abstract: When we evaluate the moral status of an action, we consider not only its consequences but also the beliefs and intentions of the actor, which relies on the capacity to infer others' mental states. Functional MRI studies showed that the right temporo-parietal junction (RTPJ) is the critical brain region for understanding others' mental states. Previous studies have found that the role of intention processing in moral judgment was reduced by disrupting the RTPJ with transcranial magnetic stimulation (TMS). In the current study, we enhanced the role of intention processing in moral judgment with the transcranial direct current sitmulation (tDCS), a painless, non-invasive brain stimulation technique that allows us to induce polarity-specific excitability changes in the human brain. Many tDCS studies have confirmed the anodal excitation effect for cognitive functions. However, so far, limited work has been done to explore the tDCS effect on social cognitive function such as moral judgment. Therefore, the present study aims to investigate the anodal excitation effect of tDCS on moral judgment. We hypothesize that exciting the neural activity of RTPJ with anodal tDCS could enhance the role of intention processing in moral judgment. To test our hypothesis, 18 healthy college students were recruited to participate in the study. All subjects underwent two tDCS sessions (anodal and sham tDCS) in random order and counterbalanced across subjects on 2 separate days with 1 week interval between both stimulations. We applied anodal (1.5mA, 20 min) and sham tDCS (1.5mA, 15 sec) on the RTPJ while subjects were introduced to keep a resting state. After stimulation, subjects read stories in a 2 (intention: negative vs. neutral) × 2 (outcome: negative vs. neutral) design and were asked to make moral judgment about how much blame the actor deserves. We analyzed the moral evaluation score and reaction time by a 2 (intention) × 2 (outcome) × 2 (tDCS: anodal, sham) repeated measures ANOVA. Results showed that actors with negative intentions were judged more morally blameworthy than those with neutral intentions, and actors producing negative outcomes were judged more blameworthy than those causing neutral outcomes. The differences between no harm (neutral intention, neutral outcome) and accidental harm (neutral intention, negative outcome) were larger than that between attempted harm (negative intention, neutral outcome) and successful harm (negative intention, negative outcome). For the reaction time, judgments of negative outcomes were faster than that of neutral outcomes. The responses to attempted and accidental harm were slower than the other two conditions. Most importantly, the moral judgment was slower under anodal tDCS than sham tDCS stimulation, especially under the attempted harm and accidental harm conditions. These results highlight the role of intention processing in moral judgment. People will spend more time integrating the intention and outcome information in order to make normal moral judgment. Furthermore, the present research provides us a better understanding about the role of RTPJ in moral judgment. Using anodal tDCS to excite the neural activity of RTPJ enhanced the capacity of mentalizing in moral judgment, especially in the cases of attempted harm and accidental harm.

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