Unilateral cerebellar stroke disrupts movement preparation and motor imagery

Objective: To assess motor cortex excitability, motor preparation and imagery in patients with unilateral cerebellar stroke with damage of the dentate nucleus by using transcranial magnetic stimulation (TMS). Method: Eight patients with unilateral cerebellar lesions due to tromboembolic stroke and 10 age matched healthy subjects were enrolled. Resting (RMT) and active (AMT) motor threshold, cortical and peripheral silent period, evaluation of motor imagery, reaction time and premovement facilitation of motor evoked potential (MEP) were tested bilaterally using TMS. Results: The RMT and AMT were found to be increased contra lateral to the affected cerebellar hemisphere while the cortical silent period was prolonged. In addition the amount of MEP facilitation during motor imagery and the pre-movement facilitation were reduced in the motor cortex contra lateral to the affected cerebellar hemisphere. The reaction time, performed with the symptomatic hand, was slower. Conclusions: On the whole, our data confirm a role for the cerebellum in maintaining the excitability of primary motor area. Furthermore, patients with unilateral cerebellar stroke exhibit lateralized deficit of motor preparation and motor imagery. Significance: Our results add to evidence that cerebellum contributes to specific aspects of motor preparation and motor imagery.