Brain maturation in children with attention-deficit hyperactivity disorder (ADHD) lags several years behind that of children with no psychiatric or neurological ailments, according to a new brain-imaging study.
Developmental delays in ADHD hit a peak of 5 years in regions at the front of the brain's outer layer, or cortex, say psychiatrist Philip Shaw of the National Institute of Mental Health in Bethesda, Md., and his colleagues. These areas assist in controlling attention and in planning upcoming actions.
Kids with ADHD display the same sequence of brain development as healthy youngsters do, the researchers find. Sensory and motor areas attain maximum thickness first, before a thinning-out process begins. Regions that integrate information from different neural sources then do the same. These findings indicate that ADHD involves a slowing, rather than a derailing, of brain maturation, Shaw argues.
A slight developmental speedup occurs in the motor cortex of children with ADHD, the researchers note. A neural mismatch between an early-maturing motor cortex and a late-maturing frontal cortex might account for the restlessness and fidgety behavior seen in ADHD, they propose.
Shaw's group used magnetic resonance imaging to gauge the thickness of neural tissue at more than 40,000 sites throughout the cortex. The researchers scanned 223 youths with ADHD and 223 typically developing children, whose ages ranged from around 7 to 13 at the study's start.
Among youngsters with ADHD, much of the cortex reached maximum thickness at an average age of 10.5, compared to age 7.5 for the others. Shaw's investigation will appear in the Proceedings of the National Academy of Sciences.
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