An Objective Estimation of Air-Bone-Gap in Cochlear Implant Recipients with Residual Hearing Using Electrocochleography

Simulating intracochlear electrocochleography with a combined model of acoustic hearing and electric current spread in the cochlea

Intracochlear electrocochleography (ECochG) is a potential tool for the assessment of residual hearing in cochlear implant users during implantation and acoustical tuning postoperatively. It is, however, unclear how these ECochG recordings from different locations in the cochlea depend on the stimulus parameters, cochlear morphology, implant design, or hair cell degeneration. In this paper, a model is presented that simulates intracochlear ECochG recordings by combining two existing models, namely a peripheral one that simulates hair cell activation and a three-dimensional (3D) volume-conduction model of the current spread in the cochlea. The outcomes were compared to actual ECochG recordings from subjects with a cochlear implant (CI). The 3D volume conduction simulations showed that the intracochlear ECochG is a local measure of activation. Simulations showed that increasing stimulus frequency resulted in a basal shift of the peak cochlear microphonic (CM) amplitude. Increasing the stimulus level resulted in wider tuning curves as recorded along the array. Simulations with hair cell degeneration resulted in ECochG responses that resembled the recordings from the two subjects in terms of CM onset responses, higher harmonics, and the width of the tuning curve. It was concluded that the model reproduced the patterns seen in intracochlear hair cell responses recorded from CI-subjects.

Amplitude growth of intracochlear electrocochleography in cochlear implant users with residual hearing

In cochlear implant (CI) users with residual hearing, the electrode-nerve interface can be investigated combining electric-acoustic stimulation (EAS) via electrocochleography (ECochG), a technique to record cochlear potentials evoked by acoustic stimulation. EAS interaction was shown in previous studies using psychoacoustic experiments. This work characterizes EAS interaction through psychophysical experiments and the amplitude growth of cochlear microphonics (CM) and auditory nerve neurophonics (ANN) derived from intracochlear ECochG recordings. Significant CM responses were recorded at psychoacoustic threshold levels. The mean difference between psychoacoustic and CM threshold was 17.5 dB. No significant ANN responses were recorded at the psychoacoustic threshold level. At the psychoacoustic most comfortable level, significant CM and ANN responses were recorded. In the presence of electrical stimulation, the psychoacoustic detection thresholds were elevated on average by 2.38 dB while the recorded CM amplitudes were attenuated on average by 1.15 dB. No significant differences in electrophysiological EAS interaction across acoustic stimulation levels were observed from CM recordings. The presence of psychophysical and electrophysiological EAS interaction demonstrates that some aspects of psychoacoustic EAS interaction can be measured via intracochlear ECochG.