With swelling prison populations, researchers are trying to understand the biology behind aggressive behavior. National Institute of Mental Health scientist Andreas Meyer-Lindenberg is looking for clues to how genes wire our brains early in life.
"One of the most fascinating things," Meyer-Lindenberg says, about this field of science called psychiatric genetics, "is how it is possible that genes [can] encode for molecules that affect something as complex as behavior, even psychiatric illness such as depression and social behavior."
He's focusing on a specific gene that was previously linked to impulsive violence. A study in 2002 found that subjects with a particular form of a gene had a significantly higher risk of violence, but only in certain populations.
Genes can affect complex behaviors like aggression, because they direct the production of proteins—the building blocks of living systems. Certain types of proteins, called enzymes, break down chemicals in the brain, most notably, serotonin—a chemical messenger in the brain that helps brains cells communicate to each other.
To isolate how a variation in this gene, called the L version of MAO-A, might affect the wiring of the brain, Meyer-Lindenberg took MRI brain scans of more than 100 healthy volunteers. Since this genetic variation is common in our population, some of the volunteers had this variation, and some didn't.
He showed them pictures of angry and fearful faces and other disturbing images, like those of an angry dog or of a gun pointed towards the screen.
As he wrote in Proceedings of the National Academy of Sciences those with the aggression-related form of the gene responded to the pictures with increased activity in the amygdala—the brain area that detects danger, but less activity in the cingulate cortex—the brain region that is believed to control aggression.
These brain patterns have been linked to impulsive violence, but Meyer-Lindenberg cautions in his paper, "because our sample was psychiatrically normal, the variation observed is clearly compatible with normal mental health and does not imply or suggest increased risk for violence in our sample."
There are many possible factors at work, he says, and violence is an extremely complex behavior. "Whether or not any given person in any given situation will become violent is known to be almost impossible to predict."
But the findings are still significant, Meyer-Lindenberg says, because, "it gives us a handle for the first time into a genetic risk for violence."
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