Abstract
The profound nature of moral judgment has been discussed and debated for centuries. When facing the trade-off between pursuing moral rights and seeking better consequences, most people make different moral choices between two kinds of dilemmas. Such differences were explained by the dual-process theory involving an automatic emotional response and a controlled application of utilitarian decision-rules. In neurocognitive studies, the bilateral dorsolateral prefrontal cortex (DLPFC) has been demonstrated to play an important role in cognitive “rational” control processes in moral dilemmas. However, the profile of results across studies is not entirely consistent. Although one transcranial magnetic stimulation (TMS) study revealed that disrupting the right DLPFC led to less utilitarian responses, other TMS studies indicated that inhibition of the right DLPFC led to more utilitarian choices. Moreover, the right temporoparietal junction (TPJ) is essential for its function of integrating belief and intention in moral judgment, which is related to the emotional process according to the dual-process theory. Relatively few studies have reported the causal relationship between TPJ and participants' moral responses, especially in moral dilemmas. In the present study, we aimed to demonstrate a direct link between the neural and behavioral results by application of transcranial direct current stimulation (tDCS) in the bilateral DLPFC or TPJ of our participants. We observed that activating the right DLPFC as well as inhibiting the left DLPFC led to less utilitarian judgments, especially in moral-personal conditions, indicating that the right DLPFC plays an essential role, not only through its function of moral reasoning but also through its information integrating process in moral judgments. It was also revealed that altering the excitability of the bilateral TPJ using tDCS negligibly altered the moral response in non-moral, moral-impersonal and moral-personal dilemmas, indicating that bilateral TPJ may have little influence over moral judgments in moral dilemmas.
Highlights
The nature of moral judgment has been debated for centuries
Response ratings from the right anodal/left cathodal transcranial direct current stimulation (tDCS) over temporoparietal junction (TPJ), left anodal/right cathodal tDCS over TPJ, right anodal/left cathodal tDCS over dorsolateral prefrontal cortex (DLPFC), left anodal/right cathodal tDCS over DLPFC and sham groups were analyzed by repeated measures analyses of variance (ANOVAs) with dilemma type as a withinsubject factor and tDCS stimulation type as a between-subject factor
Post hoc analyses (Bonferroni) revealed that in the personal dilemma tasks, the response ratings obtained in the right anodal/left cathodal DLPFC group were significantly higher than those obtained in the sham group
Summary
The nature of moral judgment has been debated for centuries. To analyze the moral brain of humans, a valid measurement is by observing participants’ responses to moral dilemmas, which present a story involving a trade-off between pursuing moral rights and seeking better consequences (Borg et al, 2006). Most people may find it appropriate to save five lives at the expense of one by turning a switch in a classic switch dilemma (Thomson, 1986), whereas in a footbridge dilemma, they may consider it inappropriate to push a stranger off the footbridge in order to stop the train, which may save the lives of five people (Greene et al, 2001) By considering both reason and emotion as essential forces in moral decisions, such differences in moral responses are explained by the dual-process theory (Greene et al, 2001, 2004). The moral emotional response is considered too strong to be overwhelmed by the cognitive reasoning process in moral-personal dilemmas while in contrast, participants may favor the utilitarian choice in moral-impersonal dilemmas because the weaker emotional response is manipulated by rational cognitive control (Greene, 2007)
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