SPATIAL-RESOLUTION OF COCHLEAR IMPLANTS - THE ELECTRICAL-FIELD AND EXCITATION OF AUDITORY AFFERENTS

This paper investigates the spatial resolution of electrical intracoch lear stimulation in order to enable further refinement of cochlear imp lants. For this purpose electrical potential distributions around a co nventional human intracochlear electrode (NUCLEUS-22) were measured in a tank, in cat cadaver cochleae and in living cat cochleae. Potential gradients were calculated where of importance. The values were compar ed to spatial tuning curves from cat primary auditory afferents in ele ctrical mono-, bi-, and various tripolar stimulation modes. Finally, a lumped element model was developed to elucidate the single fiber data . Tank potential measurements show the principal features of the diffe rent stimulation modes but are not sufficient to explain all the featu res of experimental data from single fibers. Intracochlear potential m easurements indicate an increase in spatial resolution in an apical di rection. The single fiber data also confirm that a tripolar stimulus c onfiguration provides significantly better spatial resolution than any other stimulation mode presently in use. (C) 1998 Elsevier Science B. V. All rights reserved.