All known human societies have maintained social order by enforcing compliance with social norms. The biological mechanisms underlying norm compliance are, however, hardly understood. We show that the right lateral prefrontal cortex (rLPFC) is involved in both voluntary and sanction-induced norm compliance. Both types of compliance could be changed by varying the neural excitability of this brain region with transcranial direct current stimulation, but they were affected in opposite ways, suggesting that the stimulated region plays a fundamentally different role in voluntary and sanction-based compliance. Brain stimulation had a particularly strong effect on compliance in the context of socially constituted sanctions, whereas it left beliefs about what the norm prescribes and about subjectively expected sanctions unaffected. Our findings suggest that rLPFC activity is a key biological prerequisite for an evolutionarily and socially important aspect of human behavior. It has been proposed that the human brain may have developed neural processes that support norm enforcement by generating appropriate behavioral responses to social punishment threats (7-10). However, neuroscience studies on social norms have mostly focused on the neural basis of punishing others (11-14), whereas evidence for neural circuitry underlying sanctioninduced compliance with norms is scarce. In mature adults, a brain network involving an area in the right lateral prefrontal cortex (rLPFC) is activated during norm-compliant behavior triggered by social punishment threats (10). However, it is not possible to conclude from correlative fMRI findings that norm compliance depends causally on neural activity in the rLPFC (15).Establishing such a causal dependence is crucial for our understanding of how social norm compliance develops in the context of brain maturation (16) and how it is pathologically altered and therapeutically amenable in the context of brain disorders (9). 1We employed transcranial direct current stimulation (tDCS) (17) to examine whether social norm compliance depends causally on neural processing in the previously-identified rLPFC region (10). Participants engaged via computer terminals in anonymous social interactions that had real financial consequences. In every round, participants ("Player A") received an amount of Money Units (MUs) and decided how much of it to transfer to a randomly assigned anonymous opponent ("Player B"). In baseline rounds, this transfer was implemented, whereas in punishment rounds, Player B could respond to the transfer by reducing Player A's MUs (Fig. 1, Fig. S1, Supporting Online Material, SOM, (18) Individual differences in sanction-induced norm compliance correlate with fMRImeasured activity in the rLPFC (10). Based on this finding and the rLPFC's general role in the control of behavior (22,23), it has been proposed that the rLPFC may weigh fair versus selfish responses specifically when punishment threats are present (8, 10). To provide causal evidence for this hypothesis, we first ...

Emotions seem to play a critical role in moral judgment. However, the way in which emotions exert their influence on moral judgments is still poorly understood. This study proposes a novel theoretical approach suggesting that emotions influence moral judgments based on their motivational dimension. We tested the effects of two types of induced emotions with equal valence but with different motivational implications (anger and disgust), and four types of moral scenarios (disgust-related, impersonal, personal, and beliefs) on moral judgments. We hypothesized and found that approach motivation associated with anger would make moral judgments more permissible, while disgust, associated with withdrawal motivation, would make them less permissible. Moreover, these effects varied as a function of the type of scenario: the induced emotions only affected moral judgments concerning impersonal and personal scenarios, while we observed no effects for the other scenarios. These findings suggest that emotions can play an important role in moral judgment, but that their specific effects depend upon the type of emotion induced. Furthermore, induced emotion effects were more prevalent for moral decisions in personal and impersonal scenarios, possibly because these require the performance of an action rather than making an abstract judgment. We conclude that the effects of induced emotions on moral judgments can be predicted by taking their motivational dimension into account. This finding has important implications for moral psychology, as it points toward a previously overlooked mechanism linking emotions to moral judgments.