Physical aggressiveness is associated with reduced gray matter in a key brain region, according to new neuroimaging research.

The study, published in Cortex, found that the density of brain tissue in the ventromedial prefrontal cortex (VMPFC) was linked to physical aggressiveness.

“Human violence is baggage we should have left in the Paleolithic era,” remarked study author David S. Chester, an assistant professor at Virginia Commonwealth University. “However, people keep hurting each other in spite of society’s strict sanctions against doing so.

“The durability of these aggressive tendencies suggests a strong biological basis. I conducted this study to better understand the specific ways in which our biological past impacts our aggressive present.”

The study used high-resolution scans taken using magnetic resonance imaging (MRI) to compare the brain structure of 138 young adults.

The researchers found that participants with lower gray matter density in the VMPFC were more likely to agree with statements such as “Given enough provocation, I may hit another person” and were also more likely to have been in a physical fight.

“The brain is a structure composed of many cells, which are susceptible to damage from sources ranging from car accidents, alcohol, but also early childhood experiences and genetics,” Chester explained to PsyPost. “We looked at the brains of 138 healthy, young adults and found that ‘normal’ variability in the structural health of a specific brain region (the VMPFC) was associated with greater physical aggression directed against others.”

Previous research has found that the VMPFC plays a role in processing emotional responses to harmful actions.

“These data suggest that it doesn’t require a severe brain injury or age-related brain decomposition to make someone more physically aggressive,” Chester said. “Even subtle, naturally-occurring variations in healthy people’s underlying brain structure can predict the likelihood that they will physically harm others.”

The study used a cross-sectional design, meaning the researchers cannot make conclusions about cause-and-effect relationships.

“These data are purely correlational, so we cannot say that these micro-deficits in the VMPFC cause aggressive behavior,” Chester told PsyPost. “Future work can use brain stimulation methods, such as transcranial magnetic stimulation, to temporarily disrupt brain functioning in the VMPFC. Doing so would allow us to assess whether such temporary ‘deficits’ actually cause people to act more aggressively.”

“Just because aggression has a basis in the structure of the brain does not mean that it cannot be changed,” Chester added. “The structure of the brain is very malleable and even such simple daily activities as mindfulness meditation or resisting temptation can alter brain structure in healthy adults.”

“As such, our findings do not imply that aggression is something we are stuck with due to our biology. Instead, our results give us a target that we can aim interventions, treatments, and medications at in order to attempt to make humankind less violent.”

The study, “Physical aggressiveness and gray matter deficits in ventromedial prefrontal cortex“, was co-authored by Donald R. Lynam, Richard Milich, and Nathan DeWall.