An imaging technique called orthogonal-plane fluorescence optical sectioning (OPFOS) was developed to image the internal architecture of the cochlea. Expressions for the three-dimensional point spread function and the axial and lateral resolution are derived. Methodologies for tissue preparation and for construction, alignment, calibration and characterization of an OPFOS apparatus are presented. The instrument described produced focused, high-resolution images of optical sections of an intact, excised guineapig cochlea. The lateral and axial resolutions of the images were 1 0 and 26 pm, respectively, within a 1.5-mm field of view.

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.

No abstract

Potential fields induced by nonrecessed, simple recessed, and radially varying recessed electrode designs were measured in vitro. Comparison of experimental results with theoretical analyses substantiated the experimental measurement technique and emphasized the importance of considering both nonuniform charge injection and surface electrochemistry when designing implantable stimulating electrodes. Radially varying recesses produced uniform charge injection at the electrode surface and at the aperture-tissue interface. In general, the radially varying recessed electrodes provided a combination of uniform charge injection and flexibility in design and fabrication that warrants their incorporation into all appropriate planar stimulating electrode designs.

No abstract