Children with attention deficit hyperactivity disorder (ADHD) appear to have markedly altered levels of key neurotransmitters (chemicals that carry messages between brain cells) in the frontal lobes of their brains, according to a new study.
Helen Courvoisie and colleagues used a form of magnetic resonance imaging to measure the levels of six neurotransmitter metabolites (breakdown products) in a small region of the frontal lobes of 16 children ranging in age from 6 to 12. Eight of the children were diagnosed with ADHD, while the others served as controls.
"Our data show children with ADHD had a two-and-a-half- fold increased level of glutamate, an excitatory brain chemical that can be toxic to nerve cells," Courvoisie reports. "The data also suggest a decreased level of GABA, a neuro- inhibitor. This combination may explain the behavior of children with poor impulse control." She notes that children with ADHD have multiple problems associated with impairment of the frontal lobes, which play an important role in regulating impulse control, attention, planning, and other "executive" functions.
Comments psychiatrist and ADHD researcher Russell Barkley, "Although the study is small, it is in line with previous work. It's one more brick in the wall. It is consistent with a number of other larger studies that have shown both structural and functional abnormalities in ADHD children."
The researchers note, however, that all of the children with ADHD were taking stimulant drugs which might have affected the results, although the drugs were discontinued 24 hours before the MRI scans were performed.
"Imaging children with ADHD," press release, American Medical Association, December 4, 2003. Summarizes research in the Journal of Neuropsychiatry and Clinical Neurosciences, currently in press.
"Brain differences found in ADHD kids, Amanda Gardner, HealthDay, December 5, 2003.