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Doctors can easily tell whether a child's body is growing normally. But they have a much harder time assessing the brain. Now, scientists say they've found a way to use a type of MRI scan to determine a child's brain age. The technique could help identify children with developmental problems and may also help explain what goes wrong in disorders, including autism.

NPR's Jon Hamilton reports.

JON HAMILTON: A lot of kids who have severe problems with behavior or learning get brain scans. But Nico Dosenbach, of Washington University in Saint Louis, says most of those scans don't reveal much.

Dr. NICO DOSENBACH (Pediatric Neurology Resident, St. Louis School of Medicine): We usually get a structural MRI on them just to make sure there's nothing really striking, and they usually read the scans normal.

HAMILTON: That's because the problem isn't usually with the brain structures themselves. Instead, the trouble comes from the way those structures are communicating with each other.

In typical kids, certain connections in the brain grow stronger over time, while others are pruned away. But that process seems to get delayed or derailed in children with autism and some other developmental disorders.

So Dosenbach and a team of researchers have been experimenting with a type of MRI that offers a detailed picture of communication networks in the brain. It's called functional connectivity MRI and can be done in about five minutes. Children don't have to perform any mental tasks. They just rest in the scanner.

Dr. DOSENBACH: We try to find which parts of the brain preferentially talk to which other parts. We can sort of map that out, and at the end, it essentially spits out a number that says what is your maturity level or what is your - you could call it a brain age.

HAMILTON: The brain age scale was derived from scans of more than 200 people between 7 and 30 - all of them had typical brain development. Dosenbach says the technique should be able to detect many children with problems, including autism or attention deficit disorder.

For example, he says, say, a child's connectivity scan shows a brain age of 8.

Dr. DOSENBACH: Now, if he's actually 15, you'd probably start to worry that maybe something isn't going right, and you could then use that as a warning flag to dig deep into what might be going wrong in development in this individual.

HAMILTON: Scientists say the technique may be especially important for understanding autism.

Ralph-Axel Muller is a psychologist who studies autism at San Diego State University.

Dr. RALPH-AXEL MULLER (Psychologist, San Diego State University): In many respects, the brain of a child or adolescent with autism looks somewhat immature.

HAMILTON: Muller has done several studies of children with autism using functional connectivity MRI, and he says those studies suggest a pattern. Overall, he says, important connections in the brains of these children seem to be a bit weaker, but he says the scans show that these brains also retain lots of extra connections - the type that usually get pruned away.

Dr. MULLER: So the reason why these networks don't function as well as (unintelligible) developing brain seems to be more the fact that there are these abnormal retained connections all over the place.

HAMILTON: Muller says it's not clear whether functional connectivity scans will be able to spot signs of trouble in infants, whose brain networks have just begun to develop. But, he says, the technique may finally offer scientists a better way to study autism in older children.

Dr. MULLER: I think functional connectivity can tell us a lot about the brain mechanisms that ultimately explain why children, adolescents with autism behave in the way they do.

HAMILTON: The new research appears in the journal Science.

Jon Hamilton, NPR News.

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