People with a type of traumatic brain injury that's common in war are at risk for being more aggressive than they were before the injury, according to a new study.

While the researchers specifically looked at damage to the prefrontal cortex, they found that even if the injury occurs elsewhere in the brain, expressing a certain gene could also increase the risk of aggression, the study said.

The prefrontal cortex, located near the forehead, is where social rules and knowledge are stored, said study researcher Jordan Grafman, director of traumatic brain injury research at Kessler Foundation in New Jersey.

When it is damaged, "you can't activate the social rules that inhibit you from responding aggressively as easily, and you have a higher chance, given the right provocation, of becoming aggressive," Grafman told MyHealthNewsDaily.

Grafman and his colleagues studied the aggression levels of 155 Vietnam War veterans who had suffered a penetrating traumatic brain injury, and divided them into aggressive and nonaggressive groups.

In the aggressive group, 79 percent were injured in their prefrontal cortex, whereas 21 percent were injured elsewhere in the brain, the study said.

But in the nonaggressive group, 47 percent were injured in the prefrontal cortex of the brain and 53 percent were injured elsewhere in the brain, according to the study.

"The locus of brain damage is important ... as it will clue you in to the long-term risks to the social behavior of the patient," Grafman said.

Researchers also found that a gene, called monoamine oxidase inhibitor-A (MOA-A), plays a role in aggression when people are injured elsewhere in the brain. The gene regulates aggressive behavior.

People who expressed the MAO-A gene but were not injured in the prefrontal cortex scored higher on an aggression measurement scale than people who did not express the gene, according to the study.

The findings have special relevance to war veterans who have an increased risk for traumatic brain injuries . But they would even apply to a person who has a stroke, multiple sclerosis or a closed head injury that damages the prefrontal cortex, as those injuries could also have the same impact, Grafman said.

Doctors should keep in mind that to ensure optimal care for people with this kind of injury they should combine brain-imaging, genetic testing and psychological assessments, he said.

The study was published this week in the journal Neurology.

Pass it on: If you're injured in the prefrontal cortex of the brain, or if you're injured elsewhere in your brain but possess a certain gene expression, you could have an increased risk of aggression.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.