MR shows that more isn't necessarily better in ADHD patients
Armed with MR brain mapping techniques, researchers have found that children with attention-deficit/hyperactivity disorder have too much gray matter in their temporal lobes. They note in a study published in the November 2003 issue of The Lancet that the increased amount of gray matter could complicate normal brain functions.
The temporal lobes play a part in the attentional system.
"Too much gray matter could mean that normal cellular changes like myelination and pruning of synapses, which lead to a 'loss' of gray matter in normal children, are not occurring normally in the ADHD children we studied," said Elizabeth R. Sowell, Ph.D, an assistant professor of neurology at the University of California, Los Angeles.
Sowell and colleagues used high-resolution MR as well as surface-based computation image analysis to map specific brain region size and abnormalities in 27 children and adolescents with ADHD. These patients were compared with 46 controls.
The researchers found that in addition to larger amounts of gray matter in the posterior temporal and inferior parietal cortices, ADHD patients exhibited reduced brain size in certain other brain regions, in particular the inferior portions of the dorsal prefrontal cortices. Brain size also was reduced in the anterior temporal cortices.
All abnormalities were bilateral and occurred in regions of the brain associated with attention and impulse control.
"MRI provides exquisite details of brain anatomy three dimensionally and is unparalleled by any other imaging modality for looking inside the brain," Sowell said.
While research has also looked into other techniques such as PET for imaging and possibly even diagnosing ADHD patients, reproducible results and diagnosis remain elusive. This study focused on trying to determine the etiology of brain abnormalities in order to get a better understanding of them.
Longitudinal studies are the logical next step in determining the specific structure of brain abnormalities in these patients, according to Sowell. She said that MR and brain mapping techniques would shed light on the timing of the brain abnormalities. Functional MRI could also be used to determine the efficacy of therapeutic medications.
"We are constantly striving to learn more about the underlying causes of neurodevelopmental disorders, in general," she said. "But we are particularly interested in ADHD because it affects so many children."
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