Influence of acute cerebellar lesions on somatosensory evoked potentials (SEPs) in cats

We studied the effect of acute unilateral cerebellar lesions on the cerebello-thalamo-cortical projection in cats. The lesions were classified into two groups according to their extent. In group I the lesion only covered the cerebellar cortex, while in group II both the cerebellar cortex and deep cerebellar nuclei were removed. Early (short-latency) and late (long-latency) waves, evoked by an electrical stimulation of a forelimb, were collected contralateral to the stimulated leg hemisphere. Pre- and postsurgery recordings from primary and non-primary (motor and parietal) cortices were compared. Cerebellar impairment had a strong influence on discharges of all the considered cortical areas. Early non-primary and primary responses increased in group I and remained unchanged in group II. Late somatosensory evoked potentials components were suppressed in both groups. An inhibitory influence of the cerebellar cortex on the thalamo-cortical projection was confirmed. Changes within the primary sensory cortex may suggest an engagement of that area in the compensation process of cerebellar dysfunction shortly after cerebellar lesion. An alteration in the unaffected hemisphere activation indicate that the spino-cerebellar and cerebello-cortical inputs, responsible for somatosensory evoked potentials generation, are regulated through contralateral and ipsilateral pathways. These pathways are unmasked by cerebellar lesion.