MOTOR CORTEX INHIBITION IN PATIENTS WITH ATAXIA

We studied the effects of a subthreshold magnetic stimulus over the mo tor cortex and an electrical stimulus over the cerebellum on EMG respo nses produced by suprathreshold magnetic Stimulus over the motor corte x. In normal subjects, both subthreshold conditioning stimuli and cere bellar stimuli could suppress responses to suprathreshold magnetic tes t stimuli when given at appropriate timings: ''cortico-cortical'' and ''cerebellar'' inhibition, respectively. In all patients with degenera tive ataxias and patients with a lesion in the cerebellar thalamus, th e ''cortico-cortical'' inhibition was normal and the ''cerebellar'' in hibition was absent. We conclude that cerebellar systems make no or li ttle contribution to the above-mentioned ''cortico-cortical'' inhibiti on.