In a single monkey, the surface of the cerebellum was stimulated electrically for 205 hours with electrodes and parameter values similar to those currently used inhumans for treatment of epilepsy. Impedance of stimulating and nonstimulating control electrodes remained unchanged throughout an observation period of six months. Potentials evoked by cerebellar stimulation could be recorded from the cranium, providing a noninvasive technique of determining the level of current delivered to cerebellum. Examination of the implantation site showed marked meningeal thickening surrounding the stimulating electrodes. Such thickening was not observed surrounding a control set. Light and electron microscopical examination revealed severe loss of Purkinje cells in tissue near the stimulating electrodes. There was also a moderate loss in other parts of cerebellar cortex down to a depth of about 1 mm from the exposed surface. Biochemical analysis revealed metabolic abnormalities consistent with the morphologic evidence of widespread tissue damage.
Gilman S, Dauth GW, Tennyson VM, Kremzner LT. Chronic Cerebellar Stimulation in the MonkeyPreliminary Observations. Arch Neurol. 1975;32(7):474–477. doi:10.1001/archneur.1975.00490490078008