Trait hostility modulates the impact of cathodal tDCS on frustration-induced aggression.

Aggression, particularly reactive aggression, is a key contributor to violence and public health burdens. The left ventrolateral prefrontal cortex (VLPFC) is central to downregulating and eliciting aggression, and its influence varies with trait hostility, a dispositional tendency toward mistrust and resentment. We aimed to examine whether transcranial direct current stimulation (tDCS) of the left VLPFC alters frustration-induced aggression and whether its impact is moderated by trait hostility. Ninety-nine healthy right-handed men were randomized in a double-blind, sham-controlled trial to receive anodal, cathodal, or sham tDCS while completing an unsolvable number-sequence task. Aggression was quantified using a competitive reaction time task and physiological measurements. Although frustration induction was successful across all groups, no significant group-level differences were observed in aggression or physiological responses. However, trait hostility moderated the effect of stimulation on aggressive behavior: aggression was suppressed among individuals with low hostility but was enhanced among those with high hostility, particularly under cathodal stimulation. These findings suggest that trait hostility critically influences the behavioral impact of tDCS on aggression. Taken together, these findings underscore the dual function of the left VLPFC in anger regulation and highlight the importance of tailoring neuromodulatory interventions to individual hostility levels.