Functional changes of the primary somatosensory cortex in patients with unilateral cerebellar lesions.

Although cerebellar lesions do not cause evident sensory deficits, it has been suggested recently that the cerebellum might play a role in sensory acquisition and discrimination. To determine whether the cerebellum influences the early phases of cortical somatosensory processing, we recorded cortical somatosensory evoked potentials after median nerve stimulation in five patients with unilateral cerebellar damage. We also performed a dipolar source analysis of traces by means of brain electrical source analysis. In all patients, the amplitude of the frontal N24 and parietal P24 components, as well as the strength of the corresponding dipolar sources, were significantly smaller after stimulation of the symptomatic side. These neurophysiological findings indicate that the primary somatosensory cortical processing is altered after contralateral cerebellar damage. They represent the first indication of a possible substrate for the reduction in cerebral blood flow observed in the parietal cortex after cerebellar lesion. Furthermore, the present data allow characterization of the functional influence of the cerebellar input to the primary somatosensory cortex as specifically acting over the inhibitory components of somatosensory processing.