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attention deficit hyperactivity disorder (ADHD)

Brain disconnect marks kids with ADHD

UC DAVIS—Children with attention deficit hyperactivity disorder (ADHD) often struggle with tasks that measure attention because of a disconnect between two areas of the brain, new research shows.

“This is the first time that we have direct evidence that this connectivity is missing in ADHD,” says Ali Mazaheri, postdoctoral researcher at the Center for Mind and Brain at UC Davis.

Mazaheri and his colleagues measured electrical rhythms from the brains of volunteers, especially the alpha rhythm.

When part of the brain is emitting alpha rhythms, it shows that it is disengaged from the rest of the brain and not receiving or processing information optimally, Mazaheri explains.

In the experiments, children with diagnosed ADHD and normal children were given a simple attention test while their brain waves were measured. The test consisted of being shown a red or blue image, or hearing a high or low sound, and having to react by pressing a button.

Immediately before the test, the children were shown either a letter “V” to alert them that the test would involve a picture (visual), or an inverted “V” representing the letter “A” to alert them that they would hear a sound (auditory).

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The research was originally inspired by a desire to combine laboratory and clinical research to go beyond existing measures of ADHD and get a better understanding of the condition, says Blythe Corbett, associate clinical professor of psychiatry. “Clearly the crosstalk from bedside to bench has been fruitful,” she says.

According to current models of how the brain allocates attention, signals from the frontal cortex—such as the “V” and “A” cues—should alert other parts of the brain, such as the visual processing area at the back of the head, to prepare to pay attention to something.

That should be reflected in a drop in alpha wave activity in the visual area, Mazaheri says, and that is what the researchers found in the brain waves of children without ADHD.

But children with the disorder showed no such drop in activity, indicating a disconnection between the center of the brain that allocates attention and the visual processing regions, Mazaheri explains.

“The brains of the children with ADHD apparently prepare to attend to upcoming stimuli differently than do typically developing children,” he says.

When properly cued, these children with ADHD did improve their reaction times, but don’t seem to allocate resources as efficiently, Mazaheri says.

The research appears in the current online issue of Biological Psychiatry.

This is the first evidence from brain electrical patterns for a functional disconnection in cortical attention systems in ADHD, Mazaheri says. Current definitions of ADHD are based only on behavior.

The research was originally inspired by a desire to combine laboratory and clinical research to go beyond existing measures of ADHD and get a better understanding of the condition, says Blythe Corbett, associate clinical professor of psychiatry.

“Clearly the crosstalk from bedside to bench has been fruitful,” she says.

The study was funded by grants from the National Institutes of Health, the Netherlands Organization for Scientific Research, the Perry Family Foundation, the Debber Family Foundation, and the Aristos Academy.

UC Davis  news: www.news.ucdavis.edu/

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