Remote effects of cortical dysgenesis on the primary motor cortex: evidence from the silent period following transcranial magnetic stimulation

Objective: In cortical dysgenesis (CD), animal studies suggested abnormal c ortico-cortical connections. Cerebral areas projecting to the primary motor cortex (M1) modulate the cortical silent period (CSP) following transcrani al magnetic stimulation (TMS). Therefore, we used the CSP to investigate re mote effects of CD on the M1. Methods: A detailed investigation, including single-pulse TMS and electrica l nerve stimulation, was performed in 3 consecutive adults with focal CD lo cated outside the M1 and in 18 controls. Two patients with unilateral CD we re epileptic and treated with anti-epileptic drugs. One patient with focal CD on both sides had no history of seizures. Neurological examination was n ormal in all patients. Recordings were made from both first dorsal inteross eous muscles. Results: In CD patients, the CSP was significantly lengthened contralateral ly to the affected hemispheres. In treated patients with unilateral CD, the interside difference of the CSP duration was also significantly increased. In contrast, excitability threshold, peripheral and corticospinal motor co nduction studies, and peripheral as well as ipsilateral silent periods were not significantly modified. Conclusions: Our findings indicate that focal CD outside the M1 may produce CSP modifications, which are likely due to changes of afferent control. (C ) 2000 Elsevier Science Ireland Ltd. All rights reserved.