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The drug teenagers use most is alcohol. And when teens drink, they tend to binge, downing four or five drinks in a few hours. Researchers say binge drinking has a real impact on the developing brain.

Michelle Trudeau has more.

MICHELLE TRUDEAU: The teen brain handles alcohol differently than the adult brain, says neuroscientist Susan Tapert at the University of California, San Diego. This, for several reasons.

Dr. SUSAN TAPERT (Psychiatry, University of California San Diego): First of all, the adolescent brain is still undergoing several maturational processes that render it more vulnerable to some of the effects of substances.

TRUDEAU: Vulnerable because key areas of the brain under construction during the adolescent years are more sensitive to the toxic effects of drugs such as alcohol, says Tapert. She sees this effect in the thinking and memory of teenagers who binge drink.

In a study published last month, Tapert looked at 12- to 14-year-olds before theyd ever used any alcohol or drugs. Over time, some of the kids started to drink - a few rather heavily drinking four or five drinks per occasion, two to three times a month, classic binge-drinking behavior in teens.

Dr. TAPERT: So after about three years into the study, we compared these kids who had begun to drink heavily to those who had remained non-drinkers.

TRUDEAU: And found that the binge drinkers did worse on thinking and memory tests. Plus, there was a distinct gender difference.

Dr. TAPERT: For girls who've been engaging in heavy drinking during adolescence, it looks like they're performing more poorly on tests of spatial functioning, which links to mathematics, engineering kinds of functions.

TRUDEAU: And the boys?

Dr. TAPERT: For boys who engaged in binge drinking during adolescence, we see poor performance on tests of attention - so being able to focus on something that might be somewhat boring, for a sustained period of time.

TRUDEAU: Suggesting to Tapert that alcohol disturbs the normal development of brain areas responsible for spatial functioning in girls and attention in boys.

Dr. TAPERT: The magnitude of the difference is 10 percent. I like to think of it as the difference between an A and a B.

TRUDEAU: Pediatrician and brain researcher Ron Dahl, from the University of Pittsburgh, notes that adolescents seem to have a higher tolerance for the negative effects of binge drinking, such as the ill feelings, the nausea.

Dr. RON DAHL (Pediatrician, University of Pittsburgh): Which makes it easier to consume higher amounts and enjoy some of the positive aspects. But, of course, that also creates liability for the spiral of addiction and binge use of these substances.

TRUDEAU: Dahl adds that there's a unique feature of the teenage brain that drives much of their behavior during adolescence, and that is their brains are primed and ready for intense, all-consuming learning.

Dr. DAHL: Becoming passionate about a particular activity, a particular sport, passionate about literature or changing the world or a particular religion, you'd have to keep them from doing this thing.

TRUDEAU: It's a normal, predictable part of being a teenager.

Dr. DAHL: But those same tendencies to explore, and try new things and try on new identities, may also increase the likelihood of starting in negative pathways.

TRUDEAU: Susan Tapert wanted to find out in what way binge drinking affects a teen's developing brain. So using brain imaging, she focused on what's called the white matter of the brain.

Dr. TAPERT: White matter is very important for the relay of information between brain cells. And we know that it is continuing to develop during adolescence.

TRUDEAU: So Tapert imaged two groups of high-schoolers: a group of binge drinkers, and a matched group of teens with no history of binge drinking. Tapert reports in a study published last year a marked difference in the white matter of the binge drinkers.

Dr. TAPERT: They appeared to have a number of little dings throughout their brains' white matter, indicating poor quality.

TRUDEAU: And poor quality indicates poor, inefficient communication between brain cells.

Dr. TAPERT: These results were actually surprising to me because the binge-drinking kids hadn't, in fact, engaged in a great deal of binge drinking. They were drinking on average once or twice a month. But when they did drink, it was to a relatively high quantity - of at least four or five drinks an occasion.

TRUDEAU: In another study now in press, Tapert reports abnormal functioning in the hippocampus - a key area for memory formation - in teen binge drinkers. Reflecting their abnormal brain scans, the teens did more poorly on learning verbal material.

Tapert says it's unknown if the cognitive downward slide in teenage binge drinkers is reversible.

For NPR News, I'm Michelle Trudeau.

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SHAPIRO: To see some of the brain scans from University of California study, visit npr.org.

It's MORNING EDITION from NPR News.

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