The social welfare provided by cooperation depends on the enforcement of social norms. Determining blameworthiness and assigning a deserved punishment are two cognitive cornerstones of norm enforcement. Although prior work has implicated the dorsolateral prefrontal cortex (DLPFC) in norm-based judgments, the relative contribution of this region to blameworthiness and punishment decisions remains poorly understood. Here, we used repetitive transcranial magnetic stimulation (rTMS) and fMRI to determine the specific role of DLPFC function in norm-enforcement behavior. DLPFC rTMS reduced punishment for wrongful acts without affecting blameworthiness ratings, and fMRI revealed punishment-selective DLPFC recruitment, suggesting that these two facets of norm-based decision making are neurobiologically dissociable. Finally, we show that DLPFC rTMS affects punishment decision making by altering the integration of information about culpability and harm. Together, these findings reveal a selective, causal role for DLPFC in norm enforcement: representational integration of the distinct information streams used to make punishment decisions.

In the present study, we combine brain stimulation and neuroimaging to (1) identify a selective role for DLPFC in blameworthiness versus punishment, and (2) test the integrative model of DLPFC function in norm enforcement. To that end, we exploited the fact that punishment and blameworthiness judgments have distinct information processing requirements; the former requires a decision maker to integrate representational outputs from mental state evaluation and harm severity assessment, while the latter is simply the product of mental state evaluation. First, we used a between-groups, sham-controlled repetitive transcranial magnetic stimulation (rTMS) paradigm targeting DLPFC in a sample of 66 healthy volunteers. In two separate sessions, participants were asked to make punishment and blameworthiness decisions for each of a series of hypothetical textual scenarios in which a protagonist (“John”) commits a crime. These scenarios varied both in the harm caused by the criminal act and the protagonist’s culpability. Harms ranged from simple theft to murder, while culpability varied according to the protagonist’s mental state: in some trials “John” could be held fully responsible for his actions (R trials); in other trials, duress, psychosis, or other mitigating circumstances resulted in Diminished Responsibility for his otherwise criminal behavior (DR trials). The punishment task entailed deciding how much punishment John deserved for his actions, whereas the blameworthiness task asked how morally responsible John was for his actions. We predicted that DLPFC TMS would affect punishment—but not blameworthiness—decisions and would do so by interfering with the appropriate integration of harm and culpability signals during decision making. We then used fMRI in a separate cohort of subjects to provide multi-modal convergent evidence for the selective involvement of DLPFC in punishment decision making. If the hypothesized integration function of the DLPFC in punishment decision making is correct, we would expect greater DLPFC activity when participants make punishment decisions compared to blameworthiness judgments.

This hypothesis makes several testable predictions. First, DLPFC should be particularly sensitive to decisions that require joint consideration of moral responsibility and harm severity, compared to decisions that rely only on one of them. Specifically, we predict that the involvement of DLPFC should be more evident when participants are asked to determine an appropriate punishment for a norm violation compared to when they are only instructed to rate an agent’s moral responsibility (blameworthiness) for that norm violation. This prediction is grounded in the fact that punishment decisions require representational integration from (at least) two processes (mental state evaluation and harm assessment), while blameworthiness assessments primarily hinge on mental state representations. Second, we predict that the involvement of DLPFC should be more pronounced for punishment decisions about blameworthy agents, compared to agents for whom responsibility has been mitigated by an extenuating circumstance. This the idea that supposition is predicated on responsibility judgments precede and constrain harm-based judgment (; but see). In other words, once information that reduces or eliminates the culpability of an agent is presented, information about harm is largely irrelevant to punishment, alleviating the need to integrate this information with intent representations in order to make an appropriate judgment.

Interestingly, the particular area of DLPFC engaged during norm enforcement has also been consistently observed in a range of non-social paradigms. Across the cognitive tasks in which activation in this region has been reported—such as working memory, analogical reasoning, and rule-based decision making—the unifying feature appears to be a requirement to integrate representations from multiple subtasks in order to select responses that are adaptively matched to task goals (). Extending this conceptualization of DLPFC to the domain of norm enforcement, we have recently offered an integration-and-selection hypothesis for the role of DLPFC in norm-based judgments (). According to this hypothesis, DLPFC is responsible for integrating output representations from decision-relevant subtasks during norm enforcement; this integrated signal is then used to bias response selection toward the most contextually appropriate action. For example, retributive punishment in legal contexts requires the integration of at least two main streams of information to arrive at a just sanction: (1) the severity of the criminal offense (i.e., the harm it caused); and (2) the blameworthiness of the offender (i.e., his/her moral culpability, as a function of his state of mind at the time of the offense) (). Punishment judgments are therefore the final output of an integration process that jointly considers information about the harm a defendant caused and information about his/her perceived blameworthiness for having caused it. DLPFC recruitment during decisions to punish culpable agents for criminal violations (), its reported involvement in second-party economic norm-enforcement paradigms (), and its consistency across multiple classes of norms (e.g., fairness and distributive norms, moral norms, and laws) () have led us to propose that DLPFC acts as a superordinate processing node that receives and integrates context-dependent “biasing” inputs during norm-enforcement decisions. Based on prior work, we speculate that these inputs arise from medial corticolimbic circuitry and the temporo-parietal junction (TPJ), encoding harm and blameworthiness signals, respectively (). According to this model, the output of this putative DLPFC integration process, reflecting an interaction between harm and culpability (i.e., the degree of moral blameworthiness attending to an agent’s actions), biases selection from among an array of context-specific punishment response options ().

The Good, the bad, and the just: justice sensitivity predicts neural response during moral evaluation of actions performed by others.

From moral to legal judgment: the influence of normative context in lawyers and other academics.

Functional specializations in lateral prefrontal cortex associated with the integration and segregation of information in working memory.

However, the complex nature of the norm-enforcement construct itself makes it challenging to pin down the precise role of DLPFC. Norm enforcement is not a single, unitary cognitive process, but rather comprises a range of distinct subcomponent processes. These include evaluating an agent’s action with respect to shared codes for acceptable conduct (moral permissibility); assessing the agent’s role in causing that act (causal responsibility); determining the agent’s mental state during the act—especially his intentions (moral responsibility or “blameworthiness”); appraising the outcome of the act, particularly whether and how much it harmed other people (harm assessment); and, finally, arriving at an appropriate sanction for the act (punishment) (). The challenge inherent in parsing this construct experimentally has made it difficult to selectively map DLPFC to a specific cognitive subdomain within the larger norm-enforcement construct.

Given the importance of norms for the development of modern human culture, some have suggested that human brains are especially well equipped to make norm-based judgments (). Over the last decade, functional imaging and brain stimulation work implicate one region in particular—the dorsolateral prefrontal cortex (DLPFC; specifically, the anterior aspect of brodmann area 46 sometimes referred to as rostrolateral PFC)—as being crucial for norm-enforcement. These studies show evidence of DLPFC engagement across a variety of tasks indexing moral decision making (), second-party punishment (), third-party punishment (), and norm compliance (). Some have suggested that the involvement of DLPFC across these tasks reflects cognitive control (), while others have posited that the DLPFC is necessary to assign causal responsibility to agents during norm-based judgments ().

From moral to legal judgment: the influence of normative context in lawyers and other academics.

The success of our species rests in large measure on our unique capacity for large-scale, stable cooperation among non-kin. Though the origin of this ability is an area of active study and debate, many attribute it to the development or elaboration of cognitive capacities that permit us to establish social norms, transmit them across generations, and detect and sanction their violation (). Successful cooperation today is made possible by systems of justice that inflict state-authorized costs on those who would otherwise be gleeful defectors among naive or resigned cooperators. Indeed, regardless of the specific phylogeny of human ultra-sociality, the continued stability of modern human societies hinges on our ability to enforce widely shared sentiments about appropriate behavior ().

The TMS data above indicate that transient disruption of DLPFC function affects norm-enforcement behavior. Further, the exclusive effect of DLPFC on punishment decision making (compared to blameworthiness judgments) suggests a relatively selective mapping between DLPFC function and one specific cognitive component of norm-enforcement behavior, namely punishment decision making. As a convergent test of this apparent selectivity, we compared DLPFC activity with fMRI in ten participants who were asked to make punishment and blameworthiness judgments for the same set of scenarios used in the TMS experiment. Using blood-oxygen-level-dependent (BOLD) signal extracted from our left and right DLPFC TMS stimulation target sites ( Figure 6 A, see Experimental Procedures ), we tested for DLPFC activation differences between punishment decisions and blameworthiness judgments. Consistent with prior work (), we found a significant main effect of Responsibility in right DLPFC (t= 2.41, p = 0.04), such that the BOLD signal in this brain region was higher during R than during DR trials ( Figure 6 B). This relationship was also observed in left DLPFC, albeit marginally (t= 2.12, p = 0.06). Importantly, no such relationship was observed for blameworthiness judgments in either the right ( Figure 6 B) or left DLPFC (p values > 0.4). Moreover, we found a significant judgment type difference (t= −2.23, p = 0.05), with right DLPFC more active during punishment decisions compared to blameworthiness judgments. This difference was not observed in left DLPFC (t= −0.18, p = 0.86). Taken together with the behavioral results (see Figure 1 ), these findings suggest that while Punishment decisions and Blameworthiness judgments are both sensitive to culpability differences, the use of culpability information by DLPFC is selective for Punishment.

Mediation analysis depicts coefficients and SE (italics) for the effect of rTMS on Harm and Culpability β-weights (A; culpability/harm), and the impact of these β-weights on punishment during R trials (B). Coefficients are standardized, with sign indicating the direction of the relationships. For example: path (A) indicates that DLPFC rTMS decreases the influence of harm information on punishment, and path (B) reveals that culpability betas are positively correlated with punishment. Harm-related coefficients in red, culpability-related coefficients in blue. Path (C) shows the total effect of TMS on punishment; path (C′) shows the direct effect of TMS on punishment (dashed line). Point estimates of indirect effects for both Harm and Blame signals that both fall within a 95% confidence interval that does not cross zero, unlike the direct effect of rTMS on punishment (see Results ).

If DLPFC rTMS affects punishment decision making by interfering with the integration of signals for culpability and harm, then we would expect the impact of DLPFC rTMS on punishment to be mediated by these signals ( Figure 5 ). We tested this hypothesis using a mediation analysis with rTMS condition as a predictor of punishment scores in Culpability trials, βand βas mediators, and gender and scenario set as nuisance covariates. The total effect model was significant (F= 3.74, p = 0.02), as was the total effect of rTMS on punishment (β= 0.57; 0.15–0.98, 95% confidence interval [CI]). Decomposing the total effect, we found that the direct effect of rTMS on punishment in this model was not significant (β= 0.16; −0.14–0.46, 95% CI); however, we did observe indirect effects through the two mediators (β= 0.17; 0.003–0.39, 95% CI; β= 0.24; 0.02–0.49, 95% CI). rTMS did not affect the use of harm and culpability information for blameworthiness decisions (see Supplemental Information for β-weight and mediation analyses for blameworthiness judgments). These data confirm our hypothesis that TMS modulates punishment by affecting the way that participants use information about culpability and harm in selecting appropriate third-party sanctions for norm violations.

We used a multivariate general linear model analysis to compare participants’ βand βvalues across rTMS groups (hemisphere and rTMS Condition were included as fixed factors, and sex was included as a covariate). Notably, βvalues were significantly lower in the active, compared to sham rTMS groups (F= 4.13, p = 0.047 for main effect of rTMS; p values > 0.15 for main effect of Hemisphere and for rTMS-by-Hemisphere interaction). By contrast, βvalues were significantly higher in participants exposed to DLPFC rTMS (F= 6.69, p = 0.01 for main effect of rTMS; p > 0.7 for main effect of hemisphere and for TMS-by-hemisphere interaction) ( Figure 4 B). This suggests that disrupting DLPFC function attenuates the impact of information about offender culpability while simultaneously potentiating the influence of information about harm on punishment. As an additional test of the hypothesis that DLPFC supports the integration of culpability and harm signals, we constructed the multiplicative interaction term β. This term was significantly different between rTMS groups (p < 0.05), providing further support for the notion that DLPFC performs an integration-and-selection function during third-party norm-enforcement.

(A) Negative correlation between β-weights derived from linear regression models with Harm Severity and Culpability Level as predictors. Values shown were obtained by z transforming the absolute value of β-weights for each predictor. Separate regression models were created for each participant to create per-subject β-weights.

Across all participants and all trials, both Culpability and Harm Severity were significant, unique predictors of punishment amount (Model 1, Culpability: β= − 0.77, p < 0.001; Model 2, Culpability, Harm Severity: β= −0.77, p < 0.001, β= 0.32, p < 0.001; Model 1 R= 0.6, Model 2 R= 0.71, Rchange = 0.1, p < 0.001). We then calculated punishment-based Culpability and Harm beta-weights (β-weights) for each subject. Across participants, Culpability and Harm β-weights were negatively correlated (Pearson r = −0.64, p < 0.001), suggesting that subjects differ in the relative weight that they accord to culpability and harm in their punishment decisions: that is, for a given individual, when the influence of culpability on punishment is high, the influence of harm tends to be low (and vice versa) ( Figure 4 A).

The above results suggest that DLPFC rTMS may impair the utilization of mental state information during punishment decision making in a manner that is harm sensitive. This accords well with our prediction that DLPFC rTMS would disrupt the joint consideration of Culpability and Harm during punishment decision making (). To further unpack the mechanisms through which DLPFC disruption affects punishment decisions, we ran a series of regression models to estimate the relative influence of mental state and harm information on punishment decisions for each subject and compared these estimates between rTMS groups.

Taken together, these data confirm a causal role for DLPFC in third-party norm enforcement that is selective for punishment decision making, as DLPFC rTMS did not affect blameworthiness judgments. Specifically, disrupting DLPFC function lowered the amount of punishment assigned for Responsibility scenarios. To further unpack this effect, we examined the effect of rTMS on mean punishment ratings at each level of Harm Severity separately for R and DR scenarios ( Figures 3 C and 3D). Consistent with the analyses reported above, rTMS did not significantly alter punishment at any level of Harm Severity for DR scenarios (i.e., when the agent’s culpability was reduced by extenuating circumstances; all p values > 0.3 for all harm levels; Figure 3 D). For fully culpable agents (R scenarios), we found that the effect of rTMS was stronger for low-harm compared to high-harm crimes (Property Crime: p = 0.004; Assault: p = 0.05; Maim and Rape: p = 0.20; Murder: p = 0.47). As expected, rTMS did not modulate blameworthiness ratings at any level of Harm Severity for either R or DR scenarios (all p values > 0.37; Figure 3 C). These data indicate that disrupting DLPFC function lowers punishment for culpable agents, but only when their norm violations result in low-moderate harm.

Thus, supporting our hypothesis, DLPFC rTMS selectively affected Punishment decisions about culpable agents, but not judgments of Blameworthiness. To further test this selectivity, we submitted the Punishment and Blameworthiness values for each group to a formal interaction test. This analysis revealed a significant rTMS Condition (Active versus Sham) by Judgment Type (Punishment versus Blameworthiness) interaction (F 1,3294 = 4.82, p = 0.028), such that the effect of rTMS was significantly larger for Punishment judgments compared to Blameworthiness judgments.

By contrast, we found a significant main effect of rTMS Condition (F= 4.37, p = 0.04), and a significant Culpability by rTMS Condition interaction (F= 9.94, p = 0.002) for Punishment decisions. We did not observe a significant main effect for Hemisphere, nor did we observe significant two-way (Hemisphere by rTMS Condition) or three-way (Hemisphere by rTMS Condition by Culpability) interactions (all p values > 0.05). Descriptively ( Figure 3 B), punishment ratings were lower in the Active compared to the Sham rTMS Condition for Responsibility trials (5.74 ± 0.15 versus 6.33 ± 0.15) but did not differ by rTMS Condition for Diminished Responsibility trials (0.94 ± 0.13 versus 0.98 ± 0.15, Active versus Sham, respectively). Post hoc comparisons confirmed that the effect of rTMS was significant for Responsibility trials (F= 7.78, p = 0.007), while no such effect was observed for Diminished Responsibility trials (F= 0.05, p = 0.83). These data indicate that DLPFC rTMS significantly reduced punishment for culpable criminal acts and that the magnitude of this effect did not differ as a function of which hemisphere was stimulated.

For Blameworthiness ratings, the main effect of rTMS condition was not significant (F= 0.031, p = 0.86), nor was the Culpability by rTMS Condition interaction (F= 2.57, p = 0.11). In addition, we did not observe a significant effect of Hemisphere (F= 0.02, p = 0.88), and the two-way (Hemisphere by rTMS Condition) and three-way (Hemisphere by rTMS Condition by Culpability) interactions were also not significant (p values > 0.25) ( Figure 3 A).

(C and D) The specific “locus” of the differential effect of rTMS on Punishment and Blameworthiness ratings is revealed by plotting the mean ratings across all combinations of Culpability and Harm, ordered from low Culpability/low Harm (C) to full Culpability/high Harm (D). Error bars indicate SEM.

(A and B) Mean Blameworthiness (A) and Punishment (B) Z scores as a function of TMS stimulation condition (Active versus Sham) and Culpability (colored error bars). Given that the ratings for R and DR trials occupied different portions of the scale, we z transformed the mean ratings to emphasize the difference in rTMS effects between each of the Punishment and Blameworthiness conditions.

DLPFC function was focally and transiently disrupted with rTMS. We applied 30 min of 1 Hz stimulation (Active group) or sham stimulation (Sham group) to left or right hemisphere DLPFC (see Figure 2 and Experimental Procedures ). To determine the disruptive effect of stimulation, we used a series of linear mixed effect models. Subject was treated as a random effect and rTMS stimulation condition, stimulation hemisphere, Culpability and Harm Severity, and rating were modeled as fixed effect predictors. The first set of models examined the simple effect of rTMS stimulation condition on Blameworthiness and on Punishment ratings (i.e., Blameworthiness and Punishment trials modeled separately), after accounting for variance due to Culpability and Harm Severity. The second set of models examined interactions between rTMS stimulation condition and stimulation hemisphere on Blameworthiness and on Punishment, after accounting for variance due to Culpability and Harm Severity. The third set of models examined rTMS-×-Culpability and rTMS-×-Harm Severity interactions on Blameworthiness and on Punishment. The final model tested rTMS stimulation-×-Judgment Type interactions. Parameter estimates were obtained via restricted maximum likelihood estimation. Gender and scenario set were included as covariates in all models. We did not detect an effect of rTMS stimulation on response times (see Table S1 ).

(A) Trajectory and approach angle (green funnel) calculated by Brainsight to guide coil placement for DLPFC target coordinate (red dot). Trajectory and target are visualized on a three-dimensional curvilinear surface reconstruction of one individual participant’s warped T1 MRI.

The integration-and-selection hypothesis implies that information about Culpability and Harm interact to affect Punishment. Supporting this notion, we found a significant Culpability-by-Harm Severity interaction for Punishment F= 100.93. This interaction effect appears to be driven by the steeper increase in Punishment ratings per increase in Harm Severity for R trials compared to DR trials ( Figures 1 B and 1D). We did observe a statistically significant Culpability-by-Harm Severity interaction for Blameworthiness ratings as well (F= 4.74, p = 0.003), suggesting that these two factors do interact to affect Blameworthiness assessment (see Discussion ). However, the integration-and-selection hypothesis not only implies that information about Culpability and Harm interacts to affect norm enforcement, it also predicts that this interaction will be stronger for Punishment than for Blameworthiness judgments. Consistent with this hypothesis, the Culpability-by-Harm Severity interaction was significantly stronger for Punishment decisions compared to Blameworthiness judgments (Judgment Type-by-Responsibility-by-Harm Severity three-way interaction: F= 22.04, p < 0.001). Similarly, effect sizes for the Culpability-by-Harm Severity interaction were larger for Punishment decision making (partial η= 0.63) than Blameworthiness evaluation (partial η= 0.07). Visual inspection of the interaction plots corroborate these statistical analyses: for Punishment, there was a markedly steeper increase in the amount of assigned punishment per unit increase in Harm severity, but only for trials in which the protagonist was fully responsible ( Figure 1 D). By contrast, Blameworthiness judgments were better characterized by a step function, with relatively small differences between Harm levels within R and DR trials, accompanied by a very large difference in Blameworthiness ratings between R and DR trials ( Figure 1 C). Taken as a whole, these results are consistent with our supposition that integration demands are significantly higher for Punishment decisions as compared to Blameworthiness judgments.

We found a significant effect of Culpability on both Punishment and Blameworthiness ratings ( Figures 1 A and 1B ). Across all participants, both Punishment and Blameworthiness ratings were higher for Responsibility trials compared to Diminished Responsibility trials (Punishment: F= 1,508.62, p < 0.001; Blameworthiness: F< 120.99, p = 0.001; test of within-subject effects from RM-ANOVA; Table S1 ). The main effect of Harm Severity was also significant for both Punishment (F= 221.76, p < 0.001) and Blameworthiness (F= 22.24, p < 0.001), with higher Harm Severity associated with higher ratings for both. The effect of Culpability and Harm Severity on Punishment and Blameworthiness ratings remained significant when controlling for participant gender and scenario set (see Experimental Procedures ; p < 0.001 for punishment ratings, p < 0.05 for blameworthiness ratings).

(C and D) Mean ratings across all combinations of Culpability and Harm, ordered from low Culpability/low Harm (C) to full Culpability/high Harm (D). Error bars indicate SEM.

(A and B) Mean ratings of Blameworthiness (A) and Punishment (B) as a function of Harm severity (x axis) and Culpability (colored lines).

We first examined the impact of culpability and harm severity on blameworthiness and punishment ratings within the entire sample (i.e., collapsed across sham and active conditions) by performing separate repeated-measures ANOVA (RM-ANOVA) for each judgment type (Punishment and Blameworthiness), with Culpability (R versus DR) and Harm Severity as within-subject factors (see Supplemental Information and Table S1 for response time data). Harm Severity was dummy coded as an ordinal variable according to scenario offense: 1 = Property Crime (theft and property damage), 2 = Physical Harm (simple assault), 3 = Severe Physical Harm (maiming, rapes), and 4 = Murder (murder, including combined rape and murder).

Discussion

Buckholtz and Marois, 2012 Buckholtz J.W.

Marois R. The roots of modern justice: cognitive and neural foundations of social norms and their enforcement. The principal finding of the present study is that inhibitory transcranial magnetic stimulation of the DLPFC reduces the punishment of culpable agents without affecting judgments of their blameworthiness. Norm-enforcement involves assigning blameworthiness to a norm violator based on an evaluation of causal responsibility and mental state, assessing the outcome of the norm violation (i.e., the magnitude of harm) and combining these calculations to arrive at an appropriate sanction (). The current rTMS experiment confirms that assessing blameworthiness and assigning punishment are cognitively distinct processes, with DLPFC involvement selective for the latter. fMRI provides convergent evidence for this selectivity, with (right) DLPFC activity sensitive to culpability differences during decisions about punishment but not about blameworthiness. We postulate that blameworthiness judgments are a temporally antecedent (and perhaps prerequisite) process, the output of which (i.e., culpability estimates) is used to calibrate the impact of harm severity on punishment magnitude selection. Together, these data demonstrate a selective, causal role for DLPFC in norm enforcement.

Buckholtz and Marois, 2012 Buckholtz J.W.

Marois R. The roots of modern justice: cognitive and neural foundations of social norms and their enforcement. According to our integration-and-selection model (), DLPFC combines information about harm and culpability with context-specific punishment rules (e.g., norm-specific punishment scales and culture-specific mitigating circumstances). The current findings offer support for this model in several key ways. First, we show that harm and culpability interact to determine punishment magnitude. Specifically, our suggestion that norm-based punishment requires a synthesis of harm and culpability signals is supported by the finding of a significant harm-by-responsibility interaction for punishment values, as well as a significant negative correlation between β-weights for harm and culpability predictors. Importantly, DLPFC rTMS interferes with this synthesis. First, rTMS attenuated the influence of culpability information while simultaneously increasing the influence of harm severity signals on punishment. Moreover, disrupting DLPFC affected the interaction between harm and culpability signals. Finally, mediation analysis confirms that the impact of DLPFC rTMS affects punishment by altering the effect of harm and culpability information on punishment magnitude. As a whole, these findings are consistent with the notion that DLPFC supports norm enforcement by synthesizing decision-relevant streams of information in order to bias selection from among competing response options.

Knoch et al., 2006 Knoch D.

Pascual-Leone A.

Meyer K.

Treyer V.

Fehr E. Diminishing reciprocal fairness by disrupting the right prefrontal cortex. Haushofer and Fehr, 2008 Haushofer J.

Fehr E. You shouldn’t have: your brain on others’ crimes. Several outstanding issues merit further consideration. First, we observed that DLPFC rTMS decreases mean punishment scores. On its face, this is similar to Knoch and colleagues’ finding of diminished second-party punishment in the ultimatum game following DLPFC rTMS (). While those authors attribute decreased second-party punishment to an rTMS-induced cognitive control impairment—namely, reduced inhibition of the prepotent response to receive monetary gains—this explanation is difficult to reconcile with the present data. Here, one might expect reduced inhibitory control to manifest primarily in the DR condition, when mitigating information induces a requirement to inhibit the prepotent response to punish those that have harmed others. However, significant effects of rTMS on punishment are only observed for R scenarios in the current dataset, which would not be predicted by an inhibitory control account of DLPFC function during norm enforcement. Nevertheless, while our study emphasizes the disruptive effects of DLPFC rTMS on information integration and response selection during punishment, the current data do not rule out the involvement of other related DLPFC-dependent processes (e.g., inhibitory control) in norm-enforcement behavior (); indeed, it is plausible to suggest that both integration and inhibitory control operate in tandem during norm enforcement. A more direct test of the relationship between integration-and-selection and inhibitory control during punishment awaits future work.

Third, DLPFC rTMS appears to reduce punishment by simultaneously diminishing the influence of information about culpability and enhancing the influence of information about harm severity. At first glance, one might expect that boosting the impact of harm signals would increase punishment. However, the punishment-reducing effect of TMS is only observed for low-moderate harms. For acts that result in such harms, considering the outcome may result in lower punishment than considering the malicious intent that produced that outcome. In other words, reliance on harm signals would produce a lower punishment because the actual harm that occurred is of low magnitude, while relying on culpability assessment could result in a higher punishment because the norm enforcer is punishing based on the agent’s intentions (or perhaps, on the outcome that they believe the agent desired) rather than the actual low-harm outcome. Future modeling work on punishment decision making will help better elucidate the precise nature of the computations that lead to punishment and the role that specific circuits play in representing these computations.

Saxe et al., 2006 Saxe R.

Brett M.

Kanwisher N. Divide and conquer: a defense of functional localizers. Ruff et al., 2013 Ruff C.C.

Ugazio G.

Fehr E. Changing social norm compliance with noninvasive brain stimulation. Finally, we note that the mean effect of DLPFC rTMS is relatively modest. This may be due to the fact that we used a group-based coordinate that we targeted on MNI-normalized brains. Functional localization of subject-specific DLPFC foci may prove to be a more powerful approach to stimulation-based behavioral modulation (). This technique, in combination with alternative brain stimulation methods that permit both upregulation and downregulation of cortical function (e.g., transcranial direct current stimulation), offers a particularly compelling approach to parsing the neural circuitry involved in norm-enforcement behavior ().