Study links ADHD to five brain areas

Some kids have a hard time concentrating in class or turning in homework on time. Or they might talk at times when teachers have asked for quiet. Such behaviors may point to attention deficit hyperactivity disorder, or ADHD. At least 7 in every 100 children may have this condition. Medicines and behavioral therapy — a type of talk therapy — can help treat the symptoms of this disorder. But scientists wanted to know what was behind it. Now, using brain imaging, they have just turned up five areas of the brain linked with symptoms of ADHD. At least two of those regions are smaller in kids with ADHD than in those without the disorder.

More than 80 researchers co-authored the new study. Martine Hoogman at Radboud University Medical Center in Nijmegen, the Netherlands, led this massive research team. Her group studied 1,713 people with ADHD and 1,529 others without it. That makes it the largest ADHD study to date. Its participants ranged in age from 4 to 63. They live in 23 places around the world.

The researchers scanned participants’ brains to probe what was going on inside their heads. They used magnetic resonance imaging (MRI). It relies on magnetic fields and radio waves to picture tissues deep inside the body.

By comparing brain scans of people with and without ADHD, the researchers showed that the volumes of five brain areas were smaller in kids with ADHD. The size of the entire brain also was smaller in this group. But such changes only emerged in children under age 15. No such differences showed up in adults with ADHD.

Hoogman and her colleagues shared their findings online February 15 in Lancet Psychiatry.

Where the changes showed up

The specific brain areas that differed in size in kids with and without ADHD could help explain some of the disorder’s symptoms. One affected area is the amygdala (Uh-MIG-duh-luh). This tiny structure sits in the brain’s temporal lobes. These are right above the ears. The amygdala is the hot seat for emotions. A smaller amygdala might explain problems of “children being easily frustrated, angry or irritable,” says study co-author Philip Asherson. He studies mental disorders such as ADHD at King’s College, London, in England.

The other four affected areas were the caudate (KAW-date), putamen (Pyoo-TAY-mun), accumbens (Uh-KUM-bens) and hippocampus (HIPP-oh-CAMP-us). As Asherson explains, these areas all play a big role in attention. “If something is very interesting and exciting,” he says, “most people with ADHD can focus on it. But once the initial interest goes, things start to become a little more boring.” It’s very hard for kids with ADHD to stay focused on things that they do not find stimulating, he says.

What might explain the size differences in these brain regions? Affected children might have had delays in brain development as they were growing, the authors speculate. What’s clear, they say, is that the drugs given to treat ADHD did not cause these changes. Children who had taken these drugs had similar reductions in brain volumes as those who hadn’t taken the drugs.

Jeffrey Halperin studies ADHD at Queens College in New York City. It’s part of the City University of New York. He praised the study for recruiting so many participants. Still, its findings won’t change the way that clinics treat people with ADHD today. However, he does think doctors “may become more attuned to emotional problems” in their patients now that they know that the amygdala plays a role in ADHD.

In this study, the brains were scanned just once. Halperin would like to see the scans repeated. Doing several scans over many years would provide much more information about brain development in kids with ADHD, he explains.