Encouraging new ADHD research | ADHD Information

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Hyperactive children catch up with peers, study finds
ADHD may be temporary, at least for some. A three-year developmental
lag is found.
By Denise Gellene
Los Angeles Times Staff Writer

November 13, 2007

The brains of children with attention deficit hyperactivity disorder develop
more slowly than those of other children but eventually catch up,
according to a government study published Monday that suggests ADHD
may be a transient condition, at least for some.

Using advanced imaging techniques, scientists found that the cortices of
children with ADHD reach peak thickness an average of three years later
than children without the disorder.

The cortex is involved in decision-making and supports the ability to
focus attention, remember things moment to moment and suppress
inappropriate actions -- functions often deficient in children with ADHD.

Dr. Philip Shaw of the National Institute of Mental Health, lead author of
the report, published in Proceedings of the National Academy of Sciences,
said the results might help explain why many children with ADHD appear
to grow out of the disorder and become less impulsive and fidgety as
they mature.

Shaw said that although brain development was slower among those with
ADHD, it followed a normal pattern, which should reassure parents.

"There has been a debate about whether ADHD is a delay or deviance
from normal brain development," he said. "This study comes down
strongly in favor of delay."

About 4.4 million school-age children in the U.S. have ADHD, which can
lead to poor school performance and behavior problems. Half of children
diagnosed with the disorder are treated with stimulants, such as Ritalin,
or other medicines.

Researchers used magnetic resonance imaging equipment to scan the
brains of 223 children and adolescents with ADHD and 223 youngsters
without the disorder. The scans were repeated two, three or four or more
times at three-year intervals.

Scientists focused on the cortex, which becomes thicker as the brain
builds new connections to process all the things children are learning --
a key milestone in brain development.

They measured cortical thickness at 40,000 points on each scan, creating
a detailed map of brain development in the two groups.

In general, they found that the parts of the cortex involved in sensory and
motor processing reached peak thickness earlier than the areas
responsible for decision-making and other higher-order functions.

In children with ADHD, developmental lags were most pronounced in the
prefrontal cortex, which supports attention and working memory, among
other things. Half of the cortical points in ADHD children reached peak
thickness at an average age of 10.5, contrasted with age 7.5 in children
without the disorder.

The primary motor cortex reached peak thickness at age 7.4 in children
with ADHD, about five months earlier than in normal children, researchers
found. Shaw said it was possible that the early maturation of the primary
motor cortex contributed to the fidgety behavior characteristic of ADHD.

Dr. F. Xavier Castellanos of New York University said the research helps
explain why children with ADHD often choose younger playmates, and it
should reassure parents who are worried about their children fitting in.

"They may be 11 but their brain is 8. They can't act their chronological
age," he said. "This lets parents know that having younger playmates is
OK and to be expected," said Castellanos, a former National Institute of
Mental Health researcher involved in the early stages of the study.

The study, which focused on one aspect of brain development, did not
explain why some people continue to experience ADHD symptoms as
adults.

Dr. Bradley S. Peterson of Columbia University, who was not connected to
the study, said that although the brains of children with ADHD reached
the appropriate thickness, there was no way of knowing from the study
whether individual cells were normal.

"Billions of cells make up brain tissue, and we cannot measure all the cells
and all the connections between the cells," he said. "Subtle deficits could
easily remain."

In addition, he said, the study did not examine the process of cortical
thinning that takes place in late adolescence -- a second developmental
milestone in which unneeded connections are pruned to shape the adult
brain.

Government researchers plan to continue tracking some study
participants through adulthood, Shaw said.

"We have not captured this later transition," he said. "It is possible some
people never quite get there and that is what accounts for the persistent"
ADHD.

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