ADHD — It’s all in the hands

Can certain hand movements reveal ADHD?

Two studies, both funded by the U.S. National Institutes of Health and published in the Feb. 15 issue of the journal Neurology, reveal that ADHD children have a greater amount of unintentional hand movement than children not labeled ADHD.

Researchers from Cincinnati Children’s Hospital Medical Center and the Kennedy Krieger Institute in Baltimore performed joint research using sequential finger-tapping experiments on children with ADHD. The researchers found that ADHD children exhibited more than twice the amount of unintentional movements than typical children on one of the two tests used.

Additionally, the researchers measured cortical inhibition with magnetic pulses (transcranial magnetic stimulation or TMS) and compared the results to children without ADHD.

Let’s do a little brain anatomy here to make things clearer. The cortex is a layer or sheet of neural tissue that is outermost to the cerebrum. The cortex is responsible for attention, memory, consciousness, thinking, perceptual awareness, and language. The motor cortex is a term that describes regions of the cerebral cortex. The motor cortex plays a key role in the planning, control, and execution of voluntary motor functions (like hand movement).

Cortical inhibition is a term used to describe the cortex’s ability to control these functions.  By using magnetic pulses directed across the cortex, the researchers discovered that children with ADHD were less able to inhibit their hand movements than children without ADHD. ADHD children presented unintentional hand movements about 40 percent more of the time than children without ADHD.

“We now have a real, quantifiable measure of a problem with controlling behavior in these children,” said Dr. Stewart Mostofsky, primary author of the study performed 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. “We have to recognize that and account for that in considering how to work with children with ADHD.”

Notably, ADHD children that presented the greatest inability to inhibit their hand movement usually received more severe parental reports of hyperactivity and impulsivity.

The question obviously missing is, “What is the significance of these two studies?” They do not provide any direct applications for either diagnosis or treatment of ADHD. Could any parent with an ADHD child tell the researchers that their ADHD child could not control himself like other children his age? The answer is likely a resounding, YES!

The studies do identify patterns of inhibition control. This has been documented in previous studies and is a known factor in ADHD. Could the researchers develop a diagnostic tool based on inhibition control? Yes. As a matter of fact, this type of measurement is commonly obtained in a Computerized Performance Test or “CPT.”

The CPT typically flashes a letter, number, or symbol on a computer screen. The student is tasked to press the space bar or mouse when a preselected number, letter, or symbol appears on the screen. The computer will measure how many times the student clicks correctly, incorrectly, unnecessarily, or impulsively. A wide variety of data are obtained from a CPT. Yet they can only be part of a comprehensive evaluation for evidence of ADHD as so many variables are involved that may mimic ADHD.

So, while studies like the finger tapping study are interesting, they do not provide significant insight into the field nor do they provide basis for a single method of diagnosis. One may wonder why we fund such studies given what is already known in the field.