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May 23, 2013
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Wild Young Brains


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Warning Signs of Teen Violence


   11.11.03
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Are violence and aggression genetic or a response to our upbringing? As this ScienCentral news video reports, psychologists say it's both–but parenting can shape the effects of childrens' genes.

Bad Behavior

Nurture just might trump nature when it comes to certain aspects of behavioral development. Psychologists who studied rhesus monkeys, which share over 92 percent of their genetic material with us, found that mothers not only took care of their young but also corrected any bad behavior.

"Mothers are very good at giving the kind of inputs that change behavior," says J. Dee Higley, a research psychologist at the National Institute of Alcohol Abuse and Alcoholism, "but that's happening at the very time that the brain is changing, when it needs that kind of input. It's almost as if evolution said, 'let's put mothers there so that the brain gets the right kind of input.'"

Higley and his team separated some infant monkeys from their moms and raised them only with their peers, other young monkeys. Then they looked at differences in a gene that controls a brain chemical called serotonin, which influences behavior. "Serotonin appears to be the 'brakes' of the brain," says Higley. People with a shortened copy of the serotonin gene have psychological problems like depression and anxiety.




Monkeys with a short copy of this gene have less serotonin, which tends to lead to impulsive and aggressive behavior. "If you look at monkeys who have low levels of this serotonin…[they] have difficulties getting along with other monkeys, they spend most of their time by themselves," says Higley. "When they do get with other monkeys, their encounters tend to be very short-lived."



mother and baby monkeys
image: J. Dee Higley, NIAAA
And monkeys who had the short gene and were raised by their peers had even lower levels of serotonin. But monkeys raised by their mothers had normal levels of the brain chemical, regardless of whether they had the long or short gene. "Mother-reared monkeys showed no gene difference," says Higley. "If you have the short or the long gene, they responded the same. So it wasn't just the gene, and it wasn't just the environment. It was the interaction between the two of them that produces that kind of outcome."

Because serotonin is involved in controlling behavior, Higley also looked at the monkeys' alcohol consumption, and found that "peer-bred monkeys drink more alcohol than mother-reared monkeys. But if you have that short gene, then you really drink a lot of alcohol. So the short gene exaggerated a tendency that was already there -to drink more alcohol. In mother-reared monkeys, again, there was no difference; the gene didn't make any difference whatsoever. It was only in the absence of mothers that you begin to see the effect of this gene on behavior."

Higley says that studying genes and early environment and "figuring out how they interact are ultimately what we will use to decide how we can intervene, how we can keep people from having such terrible suffering as a result of the alcohol problems or the violence problems that we see."

This research was published in the August, 2003 issue of the journal Aggressive Behavior and the January 3, 2002 issue of Molecular Psychiatry, and was funded by the National Institutes of Health.


  
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