In a second study, the researchers investigated motor control in children with ADHD further by measuring activity within the motor cortex, the part of the brain that controls voluntary movement. Researchers used Transcranial Magnetic Stimulation (TMS) to apply mild magnetic pulses for brief durations to trigger muscle activity in the hand, causing hand twitches. Researchers performed 60 trials, with single or paired pulses to measure the level of muscle activity and monitored the resulting brain activity, called short interval cortical inhibition (SICI). Overall, children with ADHD showed a substantial decrease in SICI, with significantly less inhibition of motor activity during the paired pulse stimulation compared to typically developing children. The degree of inhibition in children with ADHD, measured by SICI, was 40 percent less than typically developing children. Furthermore, within the ADHD group, less motor inhibition (decreased SICI) correlated with more severe symptoms. The measure of SICI not only predicted motor impairment in ADHD children but also robustly predicted their behavioral symptoms as reported by parents. The findings suggest that reduced SICI may be a critical biomarker of ADHD.

"The neurobiological underpinnings of motor delays and behavioral symptoms in ADHD are not well understood," said Dr. Donald Gilbert, study author and Director of the Transcranial Magnetic Stimulation Laboratory at the Cincinnati Children's Hospital Medical Center. "However, our study provides more insight into the physiological measures of this disorder. We found SICI to be an important biomarker for predicting ADHD symptoms and severity, and it is a highly quantifiable and reproducible measure. This offers a foundation for determining which children are at higher risk for severe and ongoing symptoms as they grow older."

These studies were principally supported by grants from the National Institutes of Health.

SOURCE Kennedy Krieger Institute and Cincinnati Children's Hospital Medical Center