Long-term surface stimulation of the cerebellum in the monkey. I. Light microscopic, electrophysiologic, and clinical...

The effects of chronic implantation of platinum electrodes over the surface of the cerebellum and of stimulation through these electrodes was studied in monkeys. Stimulation parameters were similar to those used in epileptic human beings; two animals received continous stimulation and two received intermittent stimulation in eight-minute on-off cycles. Both stimulating and non-stimulating electrodes became encapsulated in dense reactive fibrous tissue. As determined by light microscopy, continous stimulation resulted in widespread loss or damage to Purkinje cells. Intermittent stimulation led to damage similar in extent to mechanical damage caused by control electrodes. The impedance of the stimulating electrodes was higher after long-term than short-term implnatation and increased progressively in animals stimulated intermittently. There were no clinical neurological signs of cerebellar dysfunction, even in animals with extensive damage.