Disruption of the right temporoparietal junction with transcranial magnetic stimulation reduces the role of beliefs in moral judgments

Abstract

When we judge an action as morally right or wrong, we rely on our capacity to infer the actor's mental states (e.g., beliefs, intentions). Here, we test the hypothesis that the right temporoparietal junction (RTPJ), an area involved in mental state reasoning, is necessary for making moral judgments. In two experiments, we used transcranial magnetic stimulation (TMS) to disrupt neural activity in the RTPJ transiently before moral judgment (experiment 1, offline stimulation) and during moral judgment (experiment 2, online stimulation). In both experiments, TMS to the RTPJ led participants to rely less on the actor's mental states. A particularly striking effect occurred for attempted harms (e.g., actors who intended but failed to do harm): Relative to TMS to a control site, TMS to the RTPJ caused participants to judge attempted harms as less morally forbidden and more morally permissible. Thus, interfering with activity in the RTPJ disrupts the capacity to use mental states in moral judgment, especially in the case of attempted harms.

Fig. 1.

Experimental stimuli and design. (Upper) Combination of belief (neutral vs. negative) and outcome (neutral vs. negative) factors yielded a 2 × 2 design with four conditions. (Lower) Text of a sample “attempted harm” scenario. Bold italicized sections indicate words that differed across conditions.

Fig. 2.

Design for experiment 1 (Upper) and experiment 2 (Lower). Experiment 1 used an offline TMS paradigm in which participants received TMS at 1 Hz for 25 min and then read and responded to a series of moral scenarios. The order of TMS sessions, RTPJ first vs. control first, was counterbalanced across participants. Experiment 2 used an online TMS paradigm in which participants received TMS at 10 Hz for 500 ms. TMS onset was concurrent with onset of the moral judgment question for each story.

Fig. 3.

Results for experiment 1 (Upper) and experiment 2 (Lower). Moral judgments were made on a seven-point scale. Light bars correspond to control TMS, and dark bars correspond to RTPJ TMS. Bars represent SEM. Moral judgments of attempted harm (negative belief, neutral outcome) are significantly different by TMS site (RTPJ vs. control; *P < 0.05).