Silicone-coated thin film array cochlear implantation in a feline model

OBJECTIVES: Some limitations of cochlear implants can be attributed to a restricted spectral representation of sound provided by contemporary electrode arrays. Microfabricated high-density thin film array (TFA) technology enables a greater density of stimulating sites and, thus, a more complete spectral representation. Previous pilot cadaveric studies have documented insertion characteristics, although not electrical characteristics. STUDY DESIGN: Electrode evoked auditory brainstem response (ABR) testing in a feline model. METHODS: Six healthy, normal hearing cats were unilaterally deafened and implanted with a silicone coated TFA, measuring 27.8 × 0.4 × 80μm (L × W × H). Monopolar stimulation of single electrodes was used to evoke a triple peaked ABR. Thresholds to evoke a minimal ABR were determined. RESULTS: All 6 cats underwent successful full insertion and activation. Thresholds to evoke minimal ABR's varied among implants ranging from 75 to 450 μA. Over the basal portion of the array, thresholds were either larger or unable to evoke an ABR. CONCLUSION: Two-thirds of the implants showed ABR's along the entire array, whereas the others evoked ABR's at the apical end and less robustly more basally. This may reflect increased distance of the electrodes from the modiolus, as the basal half of the array is narrower relative to the width of the scala. A tapered design to ensure array distance to modiolus is minimized may enable the basal half of the arrays to stimulate more consistently.