THURSDAY, Nov. 10 (HealthDay News) -- Adults who were diagnosed with attention-deficit hyperactivity disorder (ADHD) as children have less gray matter in certain areas of their brains as adults than people who didn't have ADHD in their youth, researchers say.

"The majority of individuals with ADHD improve in adulthood, but it was still somewhat disappointing to see that even with improvement, there continue to be challenges for those with ADHD," said the study's lead author, Dr. F. Xavier Castellanos, a professor of child and adolescent psychiatry at New York University Langone Medical Center in New York City.

Castellanos and his team also found a trend toward even more significant brain changes in people who continued to have ADHD symptoms as adults.

Results of the study are published in the November issue of the Archives of General Psychiatry.

ADHD is a common childhood disorder, according to the U.S. National Institute of Mental Health. Symptoms include an inability to pay attention or focus, being easily distracted, becoming quickly bored, daydreaming a lot and hyperactive behavior.

Previous research has found reduced brain volume in children with ADHD, and those reductions are especially pronounced in areas of the brain that help regulate attention and emotion, according to background information in the study.

The current study included boys who had participated in an ongoing study that began in the 1970s. At that time, the study consisted of 207 white boys between the ages of 6 and 12 and 178 age-matched boys who didn't have ADHD to serve as the control group.

Castellanos's research included 59 of the study volunteers who'd had ADHD in their childhood and 80 who had not. Their average age was 41. Of the 59 with ADHD, 17 continued to have symptoms of ADHD as adults, according to the study.

The study volunteers underwent magnetic resonance imaging (MRIs) in 2002 and were interviewed about their current symptoms and medication use.

The researchers found that the outer layer of the brain (the cortex) was significantly thinner in people who'd had ADHD when they were young compared to those who hadn't had the disorder. These changes were seen in people who continued to have ADHD symptoms and in those who didn't. However, Castellanos said there was a consistent trend for those who still had symptoms to have an even thinner cortex.

The areas most affected by thinning are regions involved in "top-down control of attention and the regulation of attention," said Castellanos. For example, he explained, the amount of attention you give a task is a complex calculation of what's going on around you; how much noise there is; if something else is moving in the room and so forth. If you hear a loud noise, you're at least momentarily distracted unless you can rationally explain the noise away, such as if you're having construction done. If you can rationally explain the noise away, you can get back to work without further distraction. But, this process doesn't work as well for people with ADHD.

"To me, these kinds of studies are exciting because they get to the real neurobiology of ADHD," said Dr. Sara Hamel, a behavioral/developmental pediatrician at Children's Hospital of Pittsburgh. Hamel said some people still see ADHD as a weakness in personality or as caused by bad parenting, but this study and others like it show that "ADHD is a physiologic phenomenon and a real neurological deficit."

Both experts said that it's important for people to realize that ADHD can be a lifelong condition, and if symptoms persist into adulthood, they shouldn't be ignored.

"It's not your fault. It's something different in the way you're wired, and it's probably inherited," explained Hamel. She recommended both medications and behavioral therapy for people with ADHD.

Castellanos pointed out that almost all of the people in his study had taken stimulant medications for their ADHD, and yet the changes in the brain volume persisted into adulthood. That means that while medications can help control the symptoms of ADHD on a day to day basis, they're not likely having any impact on the underlying cause of the disease.

More information

To read more about attention-deficit hyperactivity disorder in adults, visit the U.S. National Institute of Mental Health.