Evaluation of Electrode Configurations in Cerebellar Implants

Abstract

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 a 100 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 µC in humans with 15–20 electrodes on each superior surface and 10 electrodes on each posterior cerebellar surface.

Physiological and Histological Effects of Cerebellar Stimulation

“…At a given intensity of current, the effect is greater when the currents are applied through the cerebellum. In general, the greater the number of electrodes, the greater the effect [15]. Therefore, by increasing the number of electrodes through which current is applied, a greater effect can be achieved with a lower current density at each electrode/tissue interface.…”

“…Of greater concern is the possibility of eventual loss of clinical improvement produced by cerebellar stimulation. This is not a major con sideration if currents are applied through the cerebellum from electrodes on the superior surface to those on the posterior surface, since changes at the electrode/tissue interface would not substantially affect clinical im provement associated with application of current [15,16]. Because the amount of current required for clinical improvement and for reduction in…”