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Brain Scans Reveal ADHD Differences

Some Children with ADHD May Have Different Levels of Brain Chemicals
WebMD Health News

Dec. 4, 2003 -- Children with attention deficit hyperactivity disorder (ADHD) may actually have different levels of certain chemicals in the brain than other children, a new study shows.

Using new imaging techniques, researchers found that children with the hyperactive form of ADHD had 2 1-2 times more of a brain chemical known as glutamate, which acts like a stimulant in the brain. In addition, the brains of children with this subtype of ADHD also had lower than normal levels of GABA, a chemical that has inhibitory properties in the brain.

Both of these chemicals are neurotransmitters that carry signals to and from nerve cells in the brain. Researchers say these differences may explain the behavior of children with poor impulse control.

"Glutamate is an excitatory amino acid that leads to easier stimulation and excited neuronal pathways," says researcher Helen Courvoisie, MD, assistant professor of child and adolescent psychiatry at Johns Hopkins Medical Institutions in Baltimore. "GABA is an inhibitory neurotransmitter and inhibits those pathways in the brain."

In addition to revealing differences in brain chemistry, the study also showed that these gaps correlated to the children's scores on tests of language, memory, sensory, and learning skills.

Courvoisie discussed the findings of the study Thursday at a briefing on neurological disorders sponsored by the American Medical Association in New York City. The study also appears in the December issue of the Journal of Neuropsychiatry and Clinical Neurosciences.

The Brain and ADHD

Researchers stress this is only a preliminary finding and more study is needed to confirm these results. But by better understanding the workings of the brain in children with ADHD through studies like this, they may be able to develop improved treatments. The findings may also eventually lead to the discovery of a biomarker for ADHD that could be used in screening for the condition.

The study used a variation of MRI (magnetic resonance imaging) to measure the levels of six chemicals in a small area in the frontal lobe of the brain. This area is responsible for controlling several key functions involved in ADHD, including impulse control, attention, movement, and language.

Researchers measured the levels of these brain chemicals in 16 children ages 6 to 12 years old. Eight of the children had previously been diagnosed with the hyperactive type of ADHD.

There are three types of ADD: attention deficit, hyperactive, and combined type. Most children have the combined type.

The brain imaging indicated that with children with this subtype of ADHD are exposed to higher than normal levels of excitatory brain chemicals.

However, all of the children with ADHD were taking some type of stimulant, such as Ritalin, although they did not take the medication for at least 24 hours before imaging or the psychological testing.

"We don't know if some of these effects could be due to long-term effects of Ritalin," says Courvoisie. "It is a short-acting drug, and we would think that it wouldn't, but it is possible."

In addition, researchers say they can't say at this point whether the findings of this study would apply to the other types of ADHD.

That's why Courvoisie says further studies are needed to look at the brain function in children with ADHD both on and off stimulant medication.

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