Feasibility of Using Intra-Cochlear Electrocochleography for Estimating Electrode Tonotopical Locations in CI Recipients with Residual Hearing

Hypothesis: Intra-cochlear electrocochleography provides information about electrode location in the cochlea.

Background: The Cochlear Implant (CI) is an established method for the treatment profound hearing loss. Due to favorable results and technological advancement patients with less severe hearing loss nowadays are also implanted. For patients with ski-slope hearing losses Electro Acoustic implants are available that make optimal use of the residual hearing. It will be useful to understand where each contact is located in the cochlea and use that information cochlear implant fitting. Electrocochleography (ECochG) is a tool developed to monitor acoustic hearing in CI recipients with residual hearing.

Methods: Intra-cochlear ECochG was measured in 3 subjects with good residual hearing across 125-4000 Hz. The responses were measured while changing recording electrode from basal contact (EL16) to apical contact (EL1) and varied the stimulus levels from 50 to 110 dB HL depending on the frequency.

Results: The amplitude of ECochG responses varied based on the location and level with respect to stimulus frequency. The stimulus level and electrode location curves have shown similar behavior as tuning curves with changing in ECochG response amplitudes based on electrode location. The characteristic frequency (peak amplitude) location in the cochlea varied from apical to base for low to high frequencies. The data also shown tail activity (at basal contacts) for low frequencies at high stimulus levels.

Conclusions: The intra-cochlear ECochG allowed to identify electrode locations based on measured peak ECochG amplitudes with different frequencies. The future research involves evaluating the results through CT scans and fitting CIs based on electrode locations