NIMH Study Confirms Existence of Brain Abnormalities in ADHD
Subtle structural abnormalities in the brain circuit that inhibits 
thoughts have been confirmed in the first comprehensive brain imaging 
study of Attention Deficit Hyperactivity Disorder (ADHD). Difficulty 
staying mentally focused is a primary symptom of ADHD, which affects 
about 5 percent of school age children. Magnetic Resonance Imaging (MRI) 
scans of 57 boys with ADHD, aged 5-18, also revealed that their brains 
were more symmetrical than those of 55 age-matched controls. F. Xavier 
Castellanos, M.D., of the National Institute of Mental Health and 
colleagues report on their findings in the July issue of the Archives of 
General Psychiatry. 
Three structures in the affected circuit on the right side of the brain 
-- prefrontal cortex, caudate nucleus and globus pallidus -- were 
smaller than normal in the boys with ADHD, when examined as a group. The 
prefrontal cortex, located in the frontal lobe just behind the forehead, 
is believed to serve as the brain's command center. The caudate nucleus 
and globus pallidus, located near the middle of the brain, translate the 
commands into action. "If the prefrontal cortex is the steering wheel, 
the caudate and globus are the accelerator and brakes," explained 
Castellanos. "And it's this braking or inhibitory function that is 
likely impaired in ADHD." ADHD is thought to be rooted in an inability 
to inhibit thoughts. Finding smaller right hemisphere brain structures 
responsible for such "executive" functions strengthens support for this 
hypothesis. 
The NIMH researchers also found that the entire right cerebral 
hemispheres in boys with ADHD were, on average, 5.2% smaller than those 
of controls. The right side of the brain is normally larger than the 
left. Hence, the ADHD children, as a group, had abnormally symmetrical 
brains. 
Although the same brain circuit had been implicated earlier, Castellanos 
and colleagues examined a dozen times more brain areas in a three-fold 
larger sample than had been studied previously. 
"These subtle differences, discernible when comparing group data, hold 
promise as telltale markers for future family, genetic and treatment 
studies of ADHD," said Judith Rapoport, M.D., senior author on the paper 
and chief of the NIMH Child Psychiatry Branch. "However, because of 
normal genetic variation in brain structure, MRI scans cannot be used to 
definitively diagnose the disorder in any given individual." 
The newly confirmed markers may provide clues about the causes of ADHD. 
The investigators found a significant correlation between decreased 
normal asymmetry of the caudate nucleus and histories of prenatal, 
perinatal and birth complications, leading them to speculate that events 
in the womb may affect the normal development of brain asymmetry and may 
underlie ADHD. Since there is evidence for a genetic component in at 
least some cases of ADHD, factors such as a predisposition to prenatal 
viral infections could be involved, said Dr. Rapoport. 
The NIMH researchers are currently following up on a recent discovery of 
a link between ADHD and a gene variant known to code for a particular 
receptor subtype for the neurotransmitter dopamine. "We want to see the 
extent to which children with this gene variant also have the brain 
structural abnormalities revealed in this study," said Dr. Castellanos. 
The researchers are currently extending confirmation of the markers in 
girls as well as boys who have not been exposed to medication. They are 
also using functional MRI scanning to visualize brain activity in ADHD. 
Other NIMH researchers participating in the study were: Jay Giedd, M.D., 
Wendy Marsh, Susan Hamburger, Catherine Vaituzis, Yolanda Vauss, Debra 
Kaysen, Amy Krain, Gail Ritchie, and Jagath Rajapakse. Also 
participating were: Daniel Dickstein, Brown, U.; Stacey Sarfatti, U. Of 
Pennsylvania; John Snell, Ph.D., U. Of Virginia; and Nicholas Lange, 
Ph.D., National Institute of Neurological Disorders and Stroke. 
The National Institute of Mental Health is a component of the NIH, an 
agency of the U.S. Public Health Service, part of the U.S. Department of 
Health and Human Services. 
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Jane, this is real research. No sales-speak. Focus on the issue of ADHD, 
not alcoholism. If you cannot focus, perhaps you shoud see if YOU have 
ADD.
               The Few. The Proud. The Chosen.
                     markprobe@aol.com
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