Quadrupolar stimulation for cochlear prostheses: modeling and experimental data

Cochlear implants are electrically driven in monopolar, bipolar, or common ground mode. Ideally, a quadrupolar mode is created with three colinear electrodes, where the outer poles are half the inverse polarity value of the center electrode. The resulting field is highly focused. Models of point sources show that the quadrupolar paradigm offers a greater choice of parameters to shape the field. Simulation with a lumped-parameter model of the cochlea confirms the focusing action of the quadrupole in the layers of the inner ear. Field measurements in saline solution and in the scala tympani of guinea pigs show that focusing occurs with the quadrupolar mode. It is conceivable that quadrupolar stimulation will affect the pitch place coding, reduce channel interaction and limit facial or tactile stimulation induced by current spread.