Interhemispheric interaction between the hand motor areas in patients withcortical myoclonus

Objective: To study interhemispheric interaction between the hand motor are as of both hemispheres through the corpus callosum in myoclonus epilepsy. Subjects: Five patients with benign myoclonus epilepsy and ten age matched normal volunteers. Methods: We studied effects of a medially directed conditioning stimulus ov er the right hand motor area on responses in the right first dorsal interos seous muscle to a posteriorly directed test stimulus over the left hand mot or area. Results: In normal subjects, inhibition was evoked at interstimulus interva ls (ISIs) of 8-20ms (late inhibition). In contrast, facilitation occurred i n patients at ISIs of 4-6ms (early facilitation) with no late inhibition. Conclusions: The lack of late inhibition in the patients is consistent with the idea that cortical inhibitory interneurones are affected in myoclonus epilepsy. We propose that this releases interhemispheric facilitation from powerful surround inhibition. The consequence is a predominant early facili tation between the hemispheres in patients with myoclonus epilepsy. (C) 200 1 Elsevier Science Ireland Ltd. All rights reserved.