Transcranial magnetic brain stimulation was performed in 27 children and adolescents, aged 4 to 18 years, with ADHD in the Services of Pediatric Neurology and Clinical Neurophysiology, Miguel Servet Hospital, Zaragoza, Spain. The motor evoked potential was recorded at the biceps brachii. Central motor conduction time mean value, calculated by cervical root stimulation, was very significantly increased (P<0.001) compared to normal controls. The finding reflects a delay in the maturation of the corticomotor-neuronal system. A side-to-side difference in the central motor conduction times in the ADHD group (P=.03) suggests an hemispheric asymmetry in maturation. 
COMMENT. Central motor conduction time in ADHD measured by transcranial magnetic brain stimulation may provide assistance in diagnosis and evidence supporting the theory of delayed cerebral maturation.