Figure. No caption available.
Children with attention deficit/hyperactivity disorder (ADHD) don't just have trouble controlling their attention and behavior—they also have measurable difficulties controlling specific movements. That's the conclusion of two new studies of children with ADHD published in the February 15, 2011 edition of the American Academy of Neurology's journal Neurology.
Scientists involved in the studies used two different approaches to measure “motor inhibition”—the ability to control one's movements—in children with ADHD. In the first study, 25 children ages 8–13 with ADHD, and 25 children of the same age range without ADHD, were asked to perform simple finger-sequencing movements using one hand. The scientists used video recordings and a device called an electrogoniometer to precisely measure “mirror movements”—when the opposite hand mimics the action that the other hand is doing. For example, if a child was asked to alternately tap the thumb and index finger of his right hand, his left hand might involuntarily do the same thing.
Children with ADHD had much greater “mirror overflow” than children who did not have ADHD. Even at an unconscious level, children with ADHD appear to have difficulty controlling unnecessary movements, says Stewart Mostofsky, M.D., the director of the Laboratory of Neurocognitive and Imaging Research at the Kennedy Krieger Institute in Baltimore, MD, and a member of the American Academy of Neurology (AAN), who participated in both studies.
“Just as they have difficulty controlling impulsive, hyperactive, and distractible behavior, children with ADHD seem to have difficulty controlling unnecessary movement during motor tasks,” says Dr. Mostofsky. “These difficulties may help to explain why many children with ADHD show difficulties with motor coordination and control, and often have difficulty with performing a number of tasks that involve motor skills, such as handwriting.”
The other study, involving 98 children ages 8–12, used a brain stimulation technique called transcranial magnetic stimulation (TMS) to evoke slight movements in the fingers of the dominant hands. The researchers found that a particular “braking signal” in the area of the brain responsible for motor control was less efficient in children with ADHD. Children with less of this braking signal were also the ones with the most severe motor skill impairments and behavioral ADHD symptoms.
These two studies demonstrate that specific neurologic functions can be measured safely and in a relatively short amount of time to show how the brain may be hard-wired in ADHD, says Donald Gilbert, M.D., M.S., associate professor of pediatric neurology and director of the Tourette's Syndrome and Movement Disorders Clinics and the Transcranial Magnetic Stimulation Laboratory at Cincinnati Children's Hospital Medical Center in Ohio.
“One of the problems with conditions like ADHD is that the diagnosis is based entirely on a series of observations by parents and teachers. These observations tend not to be very specific—there are, after all, a lot of reasons why a child might not be paying attention—and not very biological,” says Dr. Gilbert, who is an AAN member.
“Without an objective way to make the diagnosis of ADHD using biological measures, sometimes parents hear from others—or can't help thinking themselves—that if mom and dad had just done a better job, their child wouldn't have trouble in school,” says Dr. Gilbert. “In fact, many parents said the reason that they signed their children up for our study was that they felt blamed for the child's condition. But now, these studies show that there is a measurable neurobiological difference in these kids. Although these are not tools for clinical diagnosis, they provide a biological marker that mirrors the behavioral problems, which may help researchers conduct more studies into the biology of ADHD.”
There were some clear gender differences in the findings. In both studies, the boys with ADHD had significantly more trouble controlling unnecessary movements than children without ADHD, but the girls with ADHD did not. That makes some sense, says Dr. Mostofsky. “Girls tend to mature earlier than boys, including earlier maturation of their motor functions. We might see differences in girls at younger ages. It's also possible that boys in particular have difficulties with motor control, along with difficulties in behavioral control.”
What can parents and teachers of children with ADHD do with these findings? For starters, it's important to realize that these kids may require accommodations that will let them demonstrate what they're learning without performing a fine motor task—such as handwriting. “Children with ADHD may need accommodations in school, such as use of a keyboard and extra time to complete written assignments,” Dr. Mostofsky says. “When possible, the fine motor aspects of what has to be done in class should be minimized, to allow children with ADHD the opportunity to show their knowledge in other ways.”
And school is just the beginning, says behavioral neurologist Kenneth Heilman, M.D., James E. Rooks Jr. Distinguished Professor of Neurology at the University of Florida's Center for Movement Disorders and Neurorestoration. “A lot of activities that we do require independent movement of both hands—everything from tying shoelaces to playing the piano or guitar,” Dr. Heilman says. These studies show that such “bimanual tasks” may be particularly difficult for kids with ADHD. “If a child has mirror movements, then whatever he is doing with his right hand, he'll tend to do the same thing with his left.”
Should parents choose more bimanual tasks for their child with ADHD in an effort to improve motor control, or should they focus on activities that are more one-handed—like painting—where the child might be more immediately successful? “Parents could go either way, as long as they're careful. It's possible that training of the motor system could reduce the problem,” Dr. Heilman says. “But parents should not choose activities that will set their children up for failure. Whichever path they choose, parents and teachers should be aware of these problems and be prepared to help children cope with them.”