Anyone who's taken an introductory psychology course knows that being exposed to violence—namely, being a victim of violent abuse—can impact a person’s behavior, especially his or her impulse control and violent tendencies. 

Researchers now believe they’ve found that psychological trauma during childhood physically changes the makeup of a child’s brain, most importantly the part involved in decision-making. The results of the research by Swiss think-tank EPFL were released Tuesday in Translational Psychiatry

While the study may help to pinpoint the effect of early violence on the brain, James Keim, director of the Oppositional & Conduct Disorder Clinic at the Institute for the Advancement of Psychotherapy in San Francisco, who wasn’t involved in the study, argues that a child exposed to violence won’t necessarily grow up to be violent. 

“I’m amazed at the number of kids exposed to violence who turn out very well,” Keim, a former Child Protective Services worker, said in an interview with Healthline. “These changes, if they were inadvertently linked with violence, then we would have a much larger population of violent kids.” 

The study is yet another chapter in the ongoing debate regarding youth and violence in the United States, which has intensified in the wake of mass shootings at Sandy Hook Elementary school and an Aurora, Colorado movie theater.

Violence Triggers Changes in Specific Areas of the Brain

“This research shows that people exposed to trauma in childhood don't only suffer psychologically, but their brain also gets altered,” Professor Carmen Sandi, head of the EPFL's Laboratory of Behavioral Genetics, said in a news release. “This adds an additional dimension to the consequences of abuse, and obviously has scientific, therapeutic, and social implications.”

The most significant change researchers found was to the orbitofrontal cortex, the lower front portion of the brain behind your eyeballs.

The orbitofrontal cortex is believed to be responsible for signalling other parts of the brain about the reward or punishment offered in a given situation. This way, the mind can adapt to achieve rewards and to avoid punishment, as happens when children learn not to touch a hot stove. This region of the brain is also associated with addiction, learning social cues, and the ability to make good decisions based on potential outcomes. 

“In a challenging social situation, the orbitofrontal cortex of a healthy individual is activated in order to inhibit aggressive impulses and to maintain normal interactions,” Sandi said.

How Researchers Tested Their Theory

The researchers discovered how adolescent violence translates into aggression in adulthood by experimenting on rats. Some rats were exposed to violence during youth, and researchers tracked their behavior as they grew.

They studied the brains of the adult mice with aggressive tendencies. They found that those male rats had little activity in the orbitofrontal cortex, which reduced the rats’ ability to control their negative impulses. This also had an effect on the amygdala, another part of the brain responsible for emotional responses.

Essentially, the rats exposed to abuse didn’t have the proper chain reaction in their brains to keep them from over-reacting when they encountered something they perceived as a threat.

In the past, researchers who've studied the brains of violent human individuals—such as murderers and mobsters—have observed the same limited response from the orbitofrontal lobe and a corresponding lack of impulse control. 

“It’s remarkable,” Sandi said. “We didn’t expect to find this level of similarity.” 

Keim, however, cautions against using this kind of research as a screening tool to determine a person’s likelihood of violence. Doing that, he said, could do more harm to children than good.

“We have to be so careful about making these scientific leaps,” he said.

MAOA and the ‘Warrior Gene’

The EPFL also paid close attention to a gene, MAOA, which is associated with aggressive, antisocial, and impulsive behavior. Certain genetic variants can predispose people to an aggressive attitude, and researchers noticed that psychological stress triggered changes in how this gene behaved.

In essence, trauma changed how the rats’ genes performed permanently. When given antidepressant medication, the effect was reversed and aggressiveness decreased. 

The EPFL team noted that more research is required to determine how treatments may affect the brain’s ability to eliminate unwanted traits. 

The MAOA gene—improperly nicknamed the “warrior gene”—received attention back in 2009. A defense attorney in Tennessee argued that his client shouldn’t be held criminally liable for killing his wife’s friend and nearly killing his wife because the man carried the MAOA gene and was abused as a child. The defendant avoided the death penalty based on the evidence presented, but he was still sentenced to 32 years in prison.

While the jury is no longer out in that case, the science behind the validity of the "warrior gene" hypothesis still is.

Violence vs. Impulsive Behavior in Youth

Too often in scientific research, the term violence is used synonymously with impulsiveness. Impulsive behavior can also be triggered by a chaotic, violent environment, or when violence from an adult can’t be anticipated.

Children raised in these environments learn, to a degree, how to navigate the chaos of home, and when they’re seated in a classroom they often become bored because there aren't enough stimuli. In essence, they’ve trained themselves to function in a perpetual danger-zone.  

These children are often louder and more impulsive, and don’t do as well socially because of the way their bodies cope with stress.

Keim explained that in the face of stress, a surge of adrenaline in the body heightens visual memory but tones down hearing. So, when a child exposed to violence is in a stressful situation or feels threatened, his body blocks out what others are trying to tell him, which can make hearing cues from adults and teachers difficult. 

“Because of the adrenaline going through them, it inhibits their pro-social skills,” Keim said. 

Keim, who co-authored the book The Violence of Men, said that soldiers awarded the Medal of Honor often grew up in bad environments. He believes that training teenagers to kill in a war setting could easily change their brains in the same way as the EPFL rats exposed to violence at a young age.

“They are neurologically tuned to perform best in that kind of environment,” he said. “I’m sure you’d see those changes in any recruit in the military by the time they’re done with boot camp. If the average person is capable of these kinds of acts of violence under the right circumstances, when the first subtle signs come out, how do we treat it?”

Unlearning Learned Behavior

Much as troubled youth can become heroes of war, Keim says that sports, time spent with a mentor, and other pro-social outlets are some of the most effective ways to handle impulsive behaviors.

The largest impact is made when a child learns to self-regulate his or her “extreme adrenal responses” and when mentors teach non-violence as a social norm. This is most effective, Keim said, when the family is involved in the process and adults lead their children. 

For example, Keim said that common behavior in some parts of Oakland, Calif., is to drive around seeking vengeance when a friend is shot.

“The vast majority of violence in our society involves people doing what is in their context and the rules of their neighborhood. According to that, they’re behaving pretty normally,” he said. “They have to be taught how things go and that this is not acceptable behavior.” 

Regarding planned, large-scale acts of violence, such as the Sandy Hook and Aurora shootings, Keim said the people who commit these acts appear more normal than those who act violently on impulse, but that they have one large underlying issue: depression. 

Since men who suffer from depression may express it through violence, Keim argues that properly treating young men for mental illness before age 20 may help. “Research shows that when a person is less depressed, they are more likely to engage in pro-social behavior,” he said.