Washington Post

Sociologists, psychiatrists, criminologists and others long have struggled to understand what makes some people turn violent. Childhood abuse clearly can be a major factor in predisposing someone to violence as an adult. But researchers have wondered whether some people are born with the tendency. A study suggests some are.

In the first study of its kind, neuroscientists used the latest high-tech imaging technology to peer inside the minds of killers to try to determine whether their brains differ in some fundamental way.

"For a long time, we seemed to know that antisocial groups may be characterized by some kind of brain dysfunction. But the measure of brain dysfunction was indirect," said Andrian Raine, a clinical neuroscientist at the University of Southern California in Los Angeles who led the study.

"This is the first, the largest, and the most comprehensive brain imaging study on seriously violent crime to date."

They found evidence that some people are born with brains that may make them prone to violence, perhaps because the part of their brains involved in creating a sense of "conscience" is dysfunctional, Raine said. Raine and his colleagues identified 38 murderers and reviewed court records, attorney interviews, medical and psychological records and newspaper articles to

determine which had suffered trauma during their childhood, including physical or sexual abuse, severe neglect, extreme poverty, severe family conflict and parental divorce. Of the murderers, 12 had suffered significant abuse or deprivation. The remaining 26 experienced minimal abuse or none at all.

The researchers then used positron emission tomography (PET), a technique that can measure activity of various parts of the brain, to compare those who had suffered trauma as children with those who had not, and with a group of people who had not committed any violent acts.

Compared with the subjects who had suffered abuse and with nonviolent people, the 96 murderers from comparatively benign backgrounds averaged 5.7 percent less activity in a part of the brain known as the medial prefrontal cortex.

More significant, they showed an average of 14.2 percent less activity in a part of the medial prefrontal cortex known as the orbitofrontal cortex, on the right hemisphere. Head injuries or mental illness could not explain the differences.

The medial prefrontal cortex, located just behind the forehead, has been shown in animal research to be involved in inhibiting the limbic system, a region located much deeper inside the brain that produces aggressive behavior. "The prefrontal cortex is a bit like an emergency brake on a car. It's like the emergency brake on the deeper areas of the brain that are involved in aggressive feelings," Raine said.

Animal research also has shown that the right orbitofrontal cortex, which is just above the right eye, is involved in fear conditioning – the subconscious association between antisocial behavior and punishment that in humans is thought to be key to developing a sense of conscience.

"When you train a dog, you punish it every time it does something wrong. That's how they learn to follow social rules," Raine said. "A conscience is really just a set of conditioned responses."

The deficit revealed in the study may leave individuals with "an emotionally blunted personality lacking in conscience development." Raine and his colleagues wrote in reporting their findings last week in the journal Neuropsychiatry, Neuropsychology, and Behavioral Neurology.

The research could help explain why some people who had not suffered traumatic childhoods still become violent. "People always suspect that it was those with the adverse childhood experiences who were the ones with brain dysfunction. We found it was the ones with the benign home backgrounds who showed the dysfunction," Raine said.

"Coming from a deprived background, the reasons for your violence may be the child sexual abuse or poverty orwhatever," he said. But "if you are a violent offender, and you have a relatively normal home background, it's more likely that biological factors like brain dysfunction may be the best explanation for your violent behavior," he said.

"There are a lot of parents out there who, despite all of their best efforts, their children go off the rails and they commit violent offenses. And the parents feel desperately guilty and there's a lot of soul searching – 'What did I do wrong?' " he said. "The fact that there is an identifiable biological disposition suggests it's not how the child was raised. It's that they had a biological dysfunction, combined with a situation, that led to the violence."

Raine cautioned that human behavior is extremely complicated and tends to be influenced by a complex and often subtle interaction of social and biological factors.

"There are a lot of factors involved in crime. Brain function is just one of those," he said. "But by understanding the brain function, we will be in a much better position to understand the complete causes of violent behavior."

Other researchers praised Raine's study. But some said that while his research is interesting, they were highly skeptical that brain dysfunction alone could predispose someone to violence.