Central conduction time of magnetic brain stimulation in attention-deficit hyperactivity disorder

Twenty-seven children and adolescents aged 4 to 18 years, fulfilling the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV) criteria for attention-deficit hyperactivity disorder, were included in this study. The diagnosis was determined by a pediatric neurologist and a psychologist examined all 27 subjects with tests that included the Wechsler Intelligence Scale for Children-Revised (WISC-R) and reading, writing, handedness, personality, and anxiety scores. Subjects with histories of epilepsy, head injury, drug abuse, or psychotic disorders were excluded. Culturally based causes or emotional disorders were also excluded. Transcranial magnetic stimulation was performed on all subjects, with recording of the motor evoked potential at the biceps brachii. Central motor conduction time was calculated by cervical root stimulation. Due to shape variability, the amplitude of the motor responses was not measured in the study. The mean value of central conduction time in the subjects was very significantly increased (P < .001) compared to that in a group of normal controls, case-matched for IQ, age, and sex. A central motor conduction time greater than 12 ms indicates abnormality. A second finding in the subjects was the significant difference of central conduction time on the side-to-side stimulation (P = .03). These findings are correlated with delay in the maturation of the corticomotoneuronal system and might provide neurophysiologic data for diagnosis.