MONDAY, Feb. 14 (HealthDay News) -- Measuring hand-movement control in children with attention-deficit hyperactivity disorder may reveal insights into the brain-based differences of those with the condition, according to two new studies.
In joint research, scientists from Cincinnati Children's Hospital Medical Center and the Kennedy Krieger Institute in Baltimore performed sequential finger-tapping experiments on youngsters with ADHD, noting that they exhibited more than twice the amount of unintentional extra or "overflow" movements than typical children on one of the two measures used.
The researchers also used a device emitting magnetic pulses to children with the disorder to measure cortical inhibition -- the brain's "braking system." They found that children with ADHD were 40 percent less able than typical children to inhibit resulting hand movements.
"We now have a real, quantifiable measure of a problem with controlling behavior in these children," said Dr. Stewart Mostofsky, senior author of the finger-tapping study and director of the Laboratory for Neurocognitive and Imaging Research at the Kennedy Krieger Institute.
"From a clinical standpoint, the critical issue is ... they do have differences with these aspects of normal motor control," Mostofsky said, noting that these variations can affection handwriting, keyboard use and other fine motor skills. "We have to recognize that and account for that in considering how to work with children with ADHD."
Affecting about 8 percent of American children, ADHD is a developmental disorder characterized by inattentiveness, impulsiveness and/or hyperactivity. According to recent studies, two-thirds of those with ADHD also struggle with other mental health and developmental conditions such as anxiety and learning disabilities.
Mostofsky's study examined 50 right-handed children ages 8 to 13, including 25 with ADHD and 25 without. The participants tapped each finger in sequence to the thumb of the same hand, alternating between left and right hands. A video and electronic finger positioning device measured "excessive mirror overflow" -- defined as unintentional and unnecessary movements occurring in the same muscles on the other side of the body during finger-tapping.
Girls from each group performed similarly, but boys with ADHD exhibited nearly four times as much "mirror overflow" than typically developing boys. Notably, children with the most overflow movements had also received more severe parental reports of hyperactivity and impulsivity.
"A number of studies show that ADHD kids have motor control issues that correspond to their behavior," Mostofsky. "These overflow movements are not voluntary, conscious movements, yet they reflect a problem with inhibition. Understanding the physiologic basis of motor control gives us critical insights into ADHD."
The second study used transcranial magnetic stimulation (TMS) to apply mild magnetic pulses to the motor-control region of the brain to trigger muscle activity in the children's hands. Researchers measured the muscle twitches and monitoring the resulting brain activity, called short interval cortical stimulation, or SICI.
Not only did the children with ADHD have much greater difficulty inhibiting muscle movement, but less inhibition correlated with more severe symptoms. The findings suggest that reduced short interval cortical stimulation may be a fundamental component of ADHD, the researchers said.
Both studies, which were funded by the U.S. National Institutes of Health, are reported in the Feb. 15 print issue of the journal Neurology.
"One of the things parents say in frustration is, 'Why can no one tell me why my kid acts this way?' " said study author Dr. Donald Gilbert, director of the TMS Library at Cincinnati Children's Hospital Medical Center. "This allowed me to go from the current standard to an actual, reliable, reputable measure in the brain."
But some ADHD experts questioned the usability of the studies' findings. Dr. Andrew Adesman, chief of developmental and behavioral pediatrics at Schneider Children's Hospital in New Hyde Park, N.Y., said the research doesn't "have any immediate, direct relevance for clinicians or patients."
"From a clinical perspective, the overflow movements are irrelevant to the diagnosis of ADHD," Adesman said, adding that the study authors could have overstated "what they see as potentially the scientific implications. These are not profound papers. They're not a quantum advance in terms of science."
But mapping the brain-based differences that occur with ADHD can help people better understand the condition and help those affected, contends Dr. Craig Surman, a psychiatrist specializing in ADHD treatment at Massachusetts General Hospital in Boston.
"Being under control is not as much up to them," added Surman, also a psychiatry instructor at Harvard Medical School. "They're at the whim of a sort of loose system. This is a metaphor for how people with ADHD live their lives."
Study author Gilbert acknowledged that the research has no immediate clinical application.
"That's a challenge because then it can be difficult to find funding" for ongoing studies, he said.
To learn more about ADHD, visit the U.S. National Library of Medicine.