Abnormal rhythmic motor response in children with attention-deficit-hyperactivity disorder

Children with attention-deficit-hyperactivity disorder (ADHD) have difficulties with motor control, inhibition of motor responses, motor flexibility, and motor preparedness. We proposed that motor abnormalities in ADHD might result, at least in part, from an abnormal neuronal oscillatory mechanism necessary for motor temporal regulation. The aim of this study was to assess pacing in children with ADHD, by testing for rhythmic abnormalities of motor activity using a tapping test. Twenty-seven children (21 males, six females; aged 6 to 14 years 6 months; mean age 11 years 4 months, SD 2 years 2 months) diagnosed with ADHD according to DSM-IV clinical criteria, and 33 controls (25 males, eight females; aged 6 to 14 years 6 months; mean 11 years 1 month, SD 2 years 2 months), underwent a finger-tapping test requiring rhythmic responses to frequencies from 1 to 6 Hz. All participants who were treated on a daily basis with methylphenidate (n = 22) were medication-free on the day of the test. Most of the children with ADHD responded at a constant rate regardless of stimulus frequency, a phenomenon only seen in a small number of the controls. This specific error pattern, also seen in Parkinson's disease, has been attributed to an abnormal oscillatory mechanism mediated by dopaminergic fronto-striatal circuitry, which might also be pathophysiologically relevant for ADHD.