Evaluation of electrode configurations in cerebellar implants.

Capacitively coupled currents of 100 Hz, 0.25 msec duration, were applied to multielectrode arrays implanted upon the superior and posterior surfaces of the chimpanzee cerebellum. The current required for 90% reduction in the amplitude of the evoked potential was inversely proportional to the number of electrodes upon the cerebellar surface. A study of various waveforms showed that z Hz, 0.25 msec pulse duration is near optimal for reduction of amplitude of the somatosensory evoked potential. The current densities per electrode were 5--11 mA/cm2 with a charge per pulse of 0.04--0.08 muC in humans with 15--20 electrodes on each superior surface and 10 electrodes on each posterior cerebellar surface.