Newly discovered networks in the brain, shown here in color, go a long way toward explaining why some teenagers are more likely to start experimenting with drugs and alcohol. Diminished activity in some of these networks, discovered by two scientists at the University of Vermont and their European colleagues, makes some teens more impulsive -- and less able to inhibit urges to try alcohol, cigarettes and illegal drugs in early adolescence.

A brain network associated with impulsivity is linked to teen drug abuse, new research finds.

Teens with diminished activity in a neural network in the front part of the brain are more likely to experiment with drugs, cigarettes and alcohol in early adolescence, the researchers found. Interestingly, this network is not the same one that is linked to the impulsivity of teens with attention deficit/hyperactivity disorder (ADHD). That could mean that ADHD is not as much of a risk factor for drug abuse as researchers have worried.

"The take-home message is that impulsivity can be decomposed, broken down into different brain regions," study researcher Hugh Garavan of the University of Vermont said in a statement, "and the functioning of one region is related to ADHD symptoms, while the functioning of other regions is related to drug use."

Garavan and his colleagues scanned the brains of 1,896 14-year-olds as part of a large international project called IMAGEN. Using functional magnetic resonance imaging (fMRI), they identified parts of the brain that were linked into networks by determining which areas became more active at the same time as one another. During the scans, the teens did a task that involved pressing a button and then having to keep themselves from pressing that button at a certain cue. This task requires the brain to inhibit behavior. [Inside the Brain: A Journey Through Time]

The researchers found that a quiet orbitofrontal cortex, the part of the brain tucked behind the eyes, was linked to more experimentation with substances, and that the diminished activity likely contributed to this experimentation rather than being a cause of it.

"The differences in these networks seem to precede drug use," Garavan said.

Without an active orbitofrontal cortex network, the teens are more impulsive, said study co-author Robert Whelan, also of the University of Vermont.

When given the opportunity to smoke, drink or try drugs, the 14-year-old with a less functional impulse-regulating network will be more likely to say, "yeah, gimme, gimme, gimme!" Garavan said.

ADHD is also marked by poor impulse control, but the researchers found that the poor inhibitory control in ADHD teens was regulated by a different control network. That finding adds nuance to concerns over the risk of drug use in ADHD teens, the researchers report Sunday (April 29) in the journal Nature Neuroscience. Early educational intervention can help boost inhibitory skills, dampening impulsivity, the researchers added.

"The efficacy of these interventions may be related to the extent to which they engage the appropriate brain regions," the wrote.

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