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

Although cerebellar lesions do not cause evident sensory deficits, it has b een suggested recently that the cerebellum might play a role in sensory acq uisition and discrimination. To determine whether the cerebellum influences the early phases of cortical somatosensory processing, we recorded cortica l somatosensory evoked potentials after median nerve stimulation in five pa tients with unilateral cerebellar damage. We also performed a dipolar sourc e analysis of traces by means of brain electrical source analysis. In all p atients, the amplitude of the frontal N24 and parietal P24 components, as w ell as the strength of the corresponding dipolar sources, were significantl y smaller after stimulation of the symptomatic side. These neurophysiologic al findings indicate that the primary somatosensory cortical processing Is altered after contralateral cerebellar damage. They represent the first ind ication of a possible substrate for the reduction in cerebral blood flow ob served in the parietal cortex after cerebellar lesion, Furthermore, the pre sent data allow characterization of the functional influence of the cerebel lar input to the primary somatosensory cortex as specifically acting over t he inhibitory components of somatosensory processing.