TUESDAY, Dec. 15, 2015 (HealthDay News) -- Children with attention deficit hyperactivity disorder may have weaker connections among brain networks that help the mind focus, a new study suggests.
Using MRI brain scans from 180 children with and without ADHD, researchers found that kids with the disorder showed weaker interactions among three brain networks involved in attention.
What's more, the more severe a child's attention problems, the weaker those brain connections were.
The findings, published online Dec. 15 in the journal Biological Psychiatry, add to evidence that children with ADHD differ from other kids in the way their brains are wired.
Specifically, the study highlights the importance of the "salience network," said senior researcher Vinod Menon, a professor of psychiatry and behavioral sciences at Stanford University School of Medicine, in Stanford, Calif.
At any given moment, Menon explained, people are getting numerous pieces of information from their environment. The salience network helps the brain decide which piece deserves the most attention.
"The core brain systems involved in attention are dysfunctional in ADHD," Menon said. "There is an underlying biological aspect to these symptoms."
It's not clear, though, whether weaker connections in the salience network actually cause ADHD, according to Menon. It's possible that the root cause lies somewhere else.
"The hope," Menon said, "is that once we can identify the causes, we'll get a better handle on how to intervene with therapy."
In the United States, more than 6 million school-age children and teens have been diagnosed with ADHD, according to the U.S. Centers for Disease Control and Prevention.
The problem is, there's no objective way to help doctors diagnose the disorder, said Dr. Solomon Moshe, vice chair of neurology and pediatric neurology at Montefiore Medical Center, in New York City.
"So it's both overdiagnosed and underdiagnosed," said Moshe, who was not involved in the new study.
He said the findings are interesting from a research standpoint, and offer more insight into what's happening in the brains of at least some children with ADHD.
But for now, Moshe said, there's no way to put that information into practice -- by using brain imaging to diagnose ADHD, for example.
For one, the study showed that, as a group, children with ADHD had weaker interactions among the salience network and two other brain networks involved in focus. But that does not mean that's true of all children with ADHD, Moshe said.
Menon agreed. And, he said, it's not clear whether the brain differences his team saw are specific to ADHD: They might show up in children with various other neurological or mental health disorders, from depression to autism.
For the study, Menon's team looked at functional MRI scans from 180 children, half of whom had been diagnosed with ADHD. Functional MRI allowed researchers to chart blood flow in the brain, which served as a marker for brain activity.
All of the scans were part of a large database, and included kids from New York, Portland, Ore., and Beijing, China.
That's important, Menon said, because no matter where the children were from, the general patterns were the same: Those with ADHD typically showed weaker connections among the salience network and two related brain systems. Those systems were the default-mode network, which directs "self-referential" activities like daydreaming; and the central executive network, which is involved in short-term memory and concentration.
To create focus, the salience network has to quiet the default-mode system, while dialing up the central executive network. If the interaction among those networks is lacking, you might get stuck in a daydream rather than tackling the task at hand.
"Functional MRI can give insights into the underlying biology of ADHD," Moshe said. What's unknown, he added, is whether the pricey technology could have any value when it comes to diagnosing or monitoring children with ADHD.
Another question is whether weak connections among these three brain networks can be strengthened.
"The hope," Menon said, "is that once you work with children to improve their focus and attention, these brain circuits would be normalized."
The CDC has an overview of ADHD.