Some teenagers may be more inclined to experiment with drugs and alcohol simply because their brains work differently, making them more impulsive, a new study suggests.
The research, published in Nature Neuroscience, was the largest imaging study of the adolescent brain every conducted, involving 1,896 14-year-olds. Scientists also found that different brain networks appear to be involved in self-control problems related to substance abuse than those associated with attention deficit hyperactivity disorder, ADHD, even though both problems stem, in part, from a failure to inhibit behavior.
“The behavior might look the same, but there may be different brain regions contributing to that behavior,” says neuroimaging expert Robert Whelan at the University of Vermont, the study’s lead author.
Dr. Wheland and his colleagues used functional magnetic resonance imaging, which tracks changes in blood flow between neurons associated with mental activity. They monitored brain responses as the teenagers moved on hand in response to a stream of commands, a widely used research protocol called the “stop-signal task.” Periodically – and unpredictably – volunteers would be ordered to stop moving their hands.
The researchers identified seven neural networks active when the teenagers could stop themselves and six other active when they couldn’t.
Generally, the researchers found that the adolescents with ADHD symptoms – the most common neurodevelopmental psychiatric disorder – and those who had used drugs or alcohol had an equally hard time handling the task.
Among those with a history of alcohol, cigarette and illegal-drug use, however, they found that the impulse-control problem was associated with diminished activity in a brain region called the orbitofrontal cortex. The researchers found an entirely separate set of impulse-control networks connected with the symptoms of ADHD, distinct from those associated with adolescent substance abuse.
“Our study lends credence to the idea that ADHD and substance abuse are not intrinsically linked together,” Dr. Whelan says.
Wall Street Journal, Robert Lee Hotz, May 1, 2012