The Effects of Methylphenidate on Transcranial Magnetic Stimulation Parameters in Children with Attention Deficit Hyperactivity Disorder

Objective: The aim of this study was to investigate transcranial magnetic stimulation (TMS) parameters in children with attention deficit hyperactivity disorder (ADHD) before and after methylphenidate (MPH) treatment. Methods: Contralateral silent period (CSP), cervical latency (CL), resting motor threshold (RMT), and central motor conduction time (CMCT) were measured before and after MPH medication in 24 ADHD boys, aged between 7 and 13 years. Results: MPH treatment resulted in a significant decrease in the CMCT (p<.001). There was no significant difference in the RMT, in the CL, and in the CSP between before MPH and under MPH treatment in ADHD subjects. In addition, there was a moderate but significant negative correlation between age and the RMT (Pearson correlation= -.47; p=.03), but not with other TMS parameters (p>.05). Conclusions: The central motor conduction time (CMCT) includes the times of excitation, information processing of cortical cells, and axonal conduction time via corticospinal tract. Since MPH can not affect the axonal myelination such a short time, and since MPH did not affect CL, we speculate that the decrease in the CMCT may be imputed to increased information processing of cortical cells following MPH administration. Although previous studies suggested that information processing may be increased by MPH, further studies are warranted invastigating relationship between information processing and CMCT under the effect of MPH effect.