Reduced intracortical facilitation in patients with cerebellar degeneration

Objectives - Transcranial magnetic stimulation (TMS) was used to study intr acortical inhibitory and excitatory phenomena in patients with cerebellar a taxia. Methods - Motor evoked potentials (MEP) following single and paired TMS were recorded from the first dorsal interosseus muscle (FDI) in 15 pati ents with autosomal-dominant or idiopathic cerebellar ataxia and 15 age mat ched normal controls. Results - MEP amplitudes after paired TMS with short interstimulus intervals (1-4 ms) showing intracortical inhibition in the co ntrol group were not significantly different in the patient group. In contr ast, with longer interstimulus intervals (8-20 ms) mean MEP amplitudes were significantly reduced in the patient group, indicating a decrease of intra cortical facilitation. The mean postexcitatory inhibition after TMS was als o significantly prolonged in the patient group. Conclusion - Our findings s upport the idea that the cerebellum physiologically exerts a facilitatory i nfluence on the motor cortex which is decreased in patients with a cerebell ar degeneration.