Motor cortex changes in a patient with hemicerebellectomy.

To evaluate reorganisation of motor pathways following a cerebellar lesion, we studied motor cortex excitatory responses and inhibitory effects after transcranial stimulation, together with segmental spinal cord excitability, in one patient who had undergone hemicerebellectomy. We compared the results obtained using different forms of stimulation capable of activating the cortico-spinal tract at different sites. Results were compared between sides. We previously reported that the threshold for responses is higher in the motor cortex contralateral to the impaired hemicerebellum and the right/left threshold asymmetry is clearly greater than normal when a circular coil centred over the vertex is used. In the present study, using electrical anodal stimulation, no side difference was observed. Significant interside differences were absent also when the durations of the silent periods or the mean amplitude of the flexor carpi radialis H reflex between the two sides were compared. The outcome is that the interside differences previously observed are mainly due to reduction in the intrinsic excitability properties of the motor cortex functionally related to the impaired hemicerebellum and not to modification of the inhibitory properties of the cortex or to spinal mechanisms.