Researchers at the Kennedy Krieger Institute in Baltimore, Maryland and the Cincinnati Children’s Hospital Medical Center recently conducted two studies, both of which were published in the February issue of Neurobiology, on the ability of children with Attention Deficit and Hyperactivity Disorder (ADHD) to control impulsive movements.In the first study, “children with ADHD performed a finger-tapping task” (Science Daily). Unintentional “overflow,” or movements occurring on the opposite hand, were noted using video and a device that records finger position. Mirror overflow is “defined as unintentional and unnecessary movements occurring in the same muscles on the opposite side of the body.” The study included fifty participants, 25 with ADHD and 25 typically developing children, ages 8-12 years. All subjects completed five sequential finger-tapping tests on each hand. Children tapped each finger to their thumb of the same hand. Children alternated tapping hands between the left and the right. When children with ADHD completed left-handed finger-tapping tasks, they demonstrated twice as much mirror overflow as typically developing children. Boys with ADHD showed almost four times as much mirror overflow as typically developing peers.
Dr. Stewart Mostofsky, the study’s senior author and Director of the Laboratory for Neurocognitive and Imaging Research at the Kennedy Krieger Institute, stated, “This study used quantitative measures to support past qualitative findings that motor overflow persists to a greater degree in children with ADHD then in typically developing peers. The findings reveal that even at an unconscious level, these children are struggling with controlling and inhibiting unwanted actions and behavior.”
In the second study, researchers further examined ADHD “be measuring activity within the motor cortex, the part of the brain that controls voluntary movement.” Using Transcranial Magnetic Stimulation (TMS), researchers applied “mild magnetic pulses for brief durations to trigger muscle activity in the hand, causing hand twitches.” Researchers applied single or double pulses in 60 trials and measured the corresponding brain activity, called short interval cortical inhibition (SICI). Children with ADHD demonstrated “a substantial decrease in SICI, with significantly less inhibition of motor activity during the paired pulse stimulation compared to typically developing children.” Children with ADHD showed 40 percent less inhibition control than their typically developing peers. Additionally, children with ADHD with “less motor inhibition (decreased SICI) correlated with more severe symptoms.” Measures of SICI predicted motor impairment in children with ADHD and predicted behavioral symptoms as substantiated by parents. Researchers believe SICI “may be a critical biomarker for ADHD.”
*WebMD also posted an article about this study.