brains of children and adolescents in whom attention deficit hyperactivity
disorder is diagnosed are on average 3 percent to 4 percent smaller
in volume than those of children without the condition, according
to a large-scale government study whose findings were reported today.
the greater the severity of a child's symptoms, the greater the
discrepancy in the size of various brain areas, as measured on brain
scans, the researchers said.
in brain volume have been found before in children with the disorder,
differences that some had speculated might be a result of the medications
commonly used to treat such children.
the new work, reported today in The Journal of the American Medical
Association, found the difference was present even among children
who had never taken medication.
always been extremely cautious about overinterpreting results,"
said Dr. F. Xavier Castellanos, the lead author, who directed the
study at the National Institute of Mental Health. "But I think
this is a definitive finding and something that needs to be considered."
Dr. Castellanos, now at New York University's Child Study Center,
said the difference in overall brain size was "not huge."
smaller, the brains of the children with attention deficit hyperactivity
disorder, also referred to as A.D.H.D., followed the same progression
of development as those of the normal children. And the size difference,
Dr. Castellanos said, could not be used to diagnose the disorder,
because the difference was calculated using group averages and did
not necessarily apply in individual cases.
are some kids with A.D.H.D. that have the second largest brains
in the whole distribution," Dr. Castellanos said. It is not
clear whether the size difference between the groups was present
at birth but it did appear before school age, he said.
deficit hyperactivity disorder is characterized by distractibility,
hyperactivity and/or impulsivity, the American Psychiatric Association
diagnostic manual says.
said the study, conducted between 1991 and 2001, was the largest
of its kind and the first to follow children over time and to include
a large sample of children who had not been medicated.
researchers used magnetic resonance imaging to examine the brains
of 152 children, aged 5 to 18, who had A.D.H.D. and 139 normal children
in the same age range. Forty-nine of the children with the disorder
were scanned before they had received any medication to treat it.
have argued that Ritalin, Adderall and other drugs used to treat
attention disorders were the cause of the size differences in brain
areas reported in previous studies.
to some estimates, 1.3 million children from 5 to 14 in the United
States, most of them diagnosed with attention deficit hyperactivity
disorder, take Ritalin.
Dr. Castellanos and his colleagues found that, as in children who
had taken medication, the total brain volume of children who had
never been medicated was significantly smaller than that of children
in the control group.
study is so timely," said Dr. B. J. Casey, director of the
Sackler Institute for Developmental Biology at Weill Medical College
of Cornell University and an expert on pediatric brain imaging.
"We've all wanted to see a study like this." The study
found that the unmedicated children's brains also showed a "strikingly
smaller" volume of white matter, pale central nervous system
tissue heavy with fibers.
matter increases with age, and the unmedicated children tended to
be younger than the other participants. But Dr. Castellanos said
the finding also raised the possibility that medication might enhance
the normal maturation of the brain in children with attention disorders.
largest size difference the researchers found was in the cerebellum,
a brain structure just above the brainstem, which is involved in
muscle tone, balance, the synchronization of muscle activity and
perhaps other functions. The caudate nucleus, an area deep in the
brain that is believed to serve as a relay station for information
important in regulating attention and activity level, was also significantly
smaller in younger children with A.D.H.D.. But by the time the children
were 15, the caudate did not differ in size between the two groups.
Bradley Peterson, a professor of child psychiatry at Columbia University
who is also a brain imaging expert, called the study's methodology
"elegant" and said its findings would become a landmark.
he added, "Unfortunately, it doesn't give us a clear idea as
to where, specifically in the brain, things are going wrong for
kids with A.D.H.D.," he said.