ADHD's Brain Trail: Cerebral clues emerge for
attention disorder
Bruce Bower
Scientists have identified brain alterations that may
underlie attention-deficit hyperactivity disorder
(ADHD), a psychiatric condition that affects 3 percent
to 6 percent of U.S. school children.
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SIZED DOWN. This color-coded
image of the brain's left side depicts average
regional size differences between children with
and without ADHD. Regions in red and orange mark
where size reductions were most prominent for
children with ADHD.
UCLA
Lab. Of Neuro
Imaging |
Children and teenagers with ADHD possess less tissue
in parts of the brain's prefrontal and temporal lobes
than those without psychiatric disorders do, neurologist
Elizabeth R. Sowell of the University of California, Los
Angeles School of Medicine and her coworkers have found.
In addition, kids with ADHD display an excessive density
of the neuron-rich tissue known as gray matter in
regions of cortex toward the back of the brain, the
scientists report. The cortex is the brain's outer
layer.
These ADHD-related characteristics all occur within a
brain network that, in the research team's view,
regulates attention and controls behavior.
The new findings build on prior evidence that
youngsters with ADHD, who lack concentration,
self-control, and organizational skills, possess smaller
total brain volumes than psychiatrically healthy
children do (SN: 10/12/02, p. 227: http://www.sciencenews.org/20021012/fob1.asp).
"We're now able to localize where brain changes occur
that distinguish between kids with and without ADHD,"
Sowell says. Her team's investigation is chronicled in
the Nov. 22 Lancet.
The scientists used high-resolution magnetic
resonance imaging and a new statistical technique to
generate maps of average cortical anatomy for 27
youngsters diagnosed with ADHD and 46 others with no
psychiatric ailment. Volunteers in both groups ranged in
age from 8 to 18. About two-thirds were male.
The study found differences between the groups in
brain regions already implicated in the ability to hold
separate pieces of information in mind and to maintain
visual attention.
It's not clear why kids with ADHD showed excess gray
matter density. The researchers theorize that these
children may not develop enough white matter, the
axon-rich tissue primarily located below the cortex,
thus increasing the relative density of gray matter.
Too few children participated in the new study to
enable the researchers to probe for possible brain
disparities between boys and girls with ADHD or to rule
out possible effects of prescribed-stimulant use on
brain anatomy. A 2002 study conducted by another group
found no evidence that these medications produce
ADHD-relevant brain differences.
The new brain findings may be unique to ADHD's
symptoms, Sowell adds. Different neural patterns have
been observed in childhood ailments such as autism and
fetal alcohol syndrome, which also include attention and
behavior problems.
"Sowell's study is a step forward," remarks
psychiatrist Jay N. Giedd of the National Institute of
Mental Health in Bethesda, Md. "Still, it's puzzling and
counterintuitive that her group found increased gray
matter density in ADHD."
In other brain studies, Giedd has found smaller
cerebellums in kids with ADHD than in their ADHD-free
peers. The cerebellum, which lies at the brain's base
and thus wasn't evaluated by Sowell's group, integrates
sensations and motor functions and has numerous
connections to the frontal lobe.
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References:
Sowell, E.R., et al. 2003.
Cortical abnormalities in children and adolescents with
attention-deficit hyperactivity disorder. Lancet
362(Nov. 22):1699-1707. Summary available at http://www.thelancet.com/journal/vol362/iss9397/abs/
llan.362.9397.original_research.27787.1.
Further Readings:
Bower, B. 2002. Attention loss: ADHD
may lower volume of brain. Science News 162(Oct.
12):227. Available at http://www.sciencenews.org/20021012/fob1.asp.
Sources:
Jay N. Giedd
Child Psychiatry
Branch
National Institute of Mental
Health
Building 10, Room 4C110
10 Center Drive,
MSC 1367
Bethesda, MD 20892
Elizabeth R. Sowell
University of
California, Los Angeles
Laboratory of Neuro
Imaging
Department of Neurology
710 Westwood
Plaza, Room 4-238
Los Angeles, CA 90095-1769
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