Neural mechanisms of genetic risk for impulsivity and violence in humans

TLDR

Violence in humans is poorly understood neurobiologically, and MAOA gene variation has been linked to impulsive aggression in animals and humans. The study examined how a common MAOA polymorphism affects brain structure and function using MRI in a large healthy volunteer sample. The low‑expression MAOA allele is associated with reduced limbic volumes, heightened amygdala reactivity, and weaker prefrontal regulation, with additional orbitofrontal, hippocampal, and cingulate alterations in men, indicating that MAOA influences emotion regulation and cognitive control circuitry and may inform biological interventions for violence.

Abstract

Neurobiological factors contributing to violence in humans remain poorly understood. One approach to this question is examining allelic variation in the X-linked monoamine oxidase A (MAOA) gene, previously associated with impulsive aggression in animals and humans. Here, we have studied the impact of a common functional polymorphism in MAOA on brain structure and function assessed with MRI in a large sample of healthy human volunteers. We show that the low expression variant, associated with increased risk of violent behavior, predicted pronounced limbic volume reductions and hyperresponsive amygdala during emotional arousal, with diminished reactivity of regulatory prefrontal regions, compared with the high expression allele. In men, the low expression allele is also associated with changes in orbitofrontal volume, amygdala and hippocampus hyperreactivity during aversive recall, and impaired cingulate activation during cognitive inhibition. Our data identify differences in limbic circuitry for emotion regulation and cognitive control that may be involved in the association of MAOA with impulsive aggression, suggest neural systems-level effects of X-inactivation in human brain, and point toward potential targets for a biological approach toward violence.