Recent evidence suggests a role for cerebellum in pathophysiology of dystonia. Here we explored, the cerebellar modulation of motor cortex in patients with focal upper limb dystonia. Eight patients and eight controls underwent a transcranial magnetic stimulation protocol to study the cerebellar-brain-inhibition (CBI): a conditioning cerebellar stimulus (CCS) was followed 5 ms after by the contralateral motor cortex stimulation (test stimulus: TS). We explored the effects of CBI on MEP amplitude, short intracortical inhibition (SICI) and intracortical facilitation (ICF) measures. At baseline no differences in TS-MEP amplitude, SICI or ICF were found between patients and controls. Cerebellar-conditioning significantly reduced TS-MEP amplitude, increased ICF, and decreased SICI in control subjects. In contrast, no changes in these neurophysiological measures were observed in the motor cortex of patients, regardless of which side was tested. If further confirmed, these findings suggest a reduced cerebellar modulation of motor cortex excitability in patients with focal dystonia.
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