Reduced intracortical facilitation in patients with cerebellar degeneration.

Abstract

Transcranial magnetic stimulation (TMS) was used to study intracortical inhibitory and excitatory phenomena in patients with cerebellar ataxia. Motor evoked potentials (MEP) following single and paired TMS were recorded from the first dorsal interosseus muscle (FDI) in 15 patients with autosomal-dominant or idiopathic cerebellar ataxia and 15 age matched normal controls. MEP amplitudes after paired TMS with short interstimulus intervals (1-4 ms) showing intracortical inhibition in the control group were not significantly different in the patient group. In contrast, with longer interstimulus intervals (8-20 ms) mean MEP amplitudes were significantly reduced in the patient group, indicating a decrease of intracortical facilitation. The mean postexcitatory inhibition after TMS was also significantly prolonged in the patient group. Our findings support the idea that the cerebellum physiologically exerts a facilitatory influence on the motor cortex which is decreased in patients with a cerebellar degeneration.