Deficient intracortical inhibition in drug-naive children with attention-deficit hyperactivity disorder is enhanced by methylphenidate

In children with attention-deficit hyperactivity disorder (ADHD), motoric h yperactivity is one of the striking abnormalities. Because this symptom mig ht be due to an insufficient motor control, motor system excitability in 18 drug-naive ADHD-children aged 8-12 years was compared to 18 age-matched he althy children using the technique of transcranial magnetic stimulation (TM S). Whereas motor thresholds, cortical silent period, and intracortical fac ilitation did not differ between the two groups, ADHD-children had signific antly reduced intracortical inhibition compared to healthy controls. In all ADHD-children, a second TMS could be started after their first intake of 1 0 mg methylphenidate. Under this medication, a significant enhancement in i ntracortical inhibition could be stated. This study provides the first evid ence for inhibitory deficits within the motor cortex in ADHD-children and f or an enhancement of inhibitory mechanisms in this brain region by methylph enidate. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.