Stimulation of the Prefrontal Cortex Reduces Intentions to Commit Aggression: A Randomized, Double-Blind, Placebo-Controlled, Stratified, Parallel-Group Trial

Abstract

Although prefrontal brain impairments are one of the best-replicated brain imaging findings in relation to aggression, little is known about the causal role of this brain region. This study tests whether stimulating the dorsolateral prefrontal cortex using transcranial direct current stimulation (tDCS) reduces the likelihood of engaging in aggressive acts, and the mechanism underlying this relationship. In a double-blind, stratified, placebo-controlled, parallel-group, randomized trial, 81 human adults (36 males, 45 females) were randomly assigned to an active (N = 39) or placebo (N = 42) condition, and then followed up 1 d after the experiment session. Intentions to commit aggressive acts and behavioral aggression were assessed using hypothetical vignettes and a behavioral task, respectively. The secondary outcome was the perception of the moral wrongfulness of the aggressive acts. Compared with the sham controls, participants who received anodal stimulation reported being less likely to commit physical and sexual assault (p < 0.01). They also judged aggressive acts as more morally wrong (p < 0.05). Perceptions of greater moral wrongfulness regarding the aggressive acts accounted for 31% of the total effect of tDCS on intentions to commit aggression. Results provide experimental evidence that increasing activity in the prefrontal cortex can reduce intentions to commit aggression and enhance perceptions of the moral wrongfulness of the aggressive acts. Findings shed light on the biological underpinnings of aggression and theoretically have the potential to inform future interventions for aggression and violence.SIGNIFICANCE STATEMENT Aggressive behaviors pose significant public health risks. Understanding the etiology of aggression is paramount to violence reduction. Investigations of the neural basis of aggression have largely supported correlational, rather than causal, interpretations, and the mediating processes underlying the prefrontal-aggression relationship remain to be well elucidated. Through a double-blind, stratified, placebo-controlled, parallel-group, randomized trial, this study tested whether upregulation of the prefrontal cortex reduces the likelihood of engaging in aggression. Results provide experimental evidence that increasing prefrontal cortical activity can reduce intent to commit aggressive acts. They also shed light on moral judgment as one mechanism that may link prefrontal deficits to aggression and, in theory, have the potential to inform future approaches toward reducing aggression.

Keywords: aggression; moral judgment; prefrontal; transcranial direct current stimulation; violence.

Copyright © 2018 the authors 0270-6474/18/386505-08$15.00/0.

Figures

Figure 1.

CONSORT (Consolidated Standards of Reporting Trials) flowchart of the screening and enrollment of study participants who were randomly assigned to anodal prefrontal stimulation or a sham control group.

Figure 2.

A–C, Group means for (A) aggressive intent, (B) behavioral aggression, and (C) perceptions of moral wrongfulness at follow-up. *p < .05, **p < .01. Extended data are presented in Figure 2-1.

Figure 3.

Bootstrapped mediation model documenting that perceptions of greater moral wrongfulness mediated the effect of anodal tDCS on reducing intentions to commit aggression. *p < .05, **p < .01. Extended data are presented in Figure 3-1.