Abstract
Objective: Lay the groundwork for using electrocochleography (ECochG) as a measure of cochlear health, by characterizing typical patterns of the ECochG response observed across the electrode array in cochlear implant recipients with residual hearing.Methods: ECochG was measured immediately after electrode insertion in 45 cochlear implant recipients with residual hearing. The Cochlear Response Telemetry system was used to record ECochG across the electrode array, in response to 100- or 110-dB SPL pure tones at 0.5-kHz, presented at 14 per second and with alternating polarities. Hair cell activity, as the cochlear microphonic (CM), was estimated by taking the difference (DIF) of the two polarities. Neural activity, as the auditory nerve neurophonic (ANN), was estimated by taking the sum (SUM) of the two polarities. Prior work in humans and animal studies suggested that the expected ECochG pattern in response to a 0.5-kHz pure tone is an apical-peak in CM amplitude and latency.Results: The most prevalent pattern was a peak in the DIF amplitude near the most apical electrode, with a prolongation of latency toward the electrode tip; this was found in 21/39 individuals with successful ECochG recordings. The 21 apical-peak recipients had the best low-frequency hearing. A low amplitude, long-latency DIF response that remained relatively constant across the electrode array was found in 10/39 individuals, in a group with the poorest low- and high-frequency hearing. A third, previously undescribed, pattern occurred in 8/39 participants, with mid-electrode peaks in DIF amplitude. These recipients had the best high-frequency hearing and a progressive prolongation of DIF latency around the mid-electrode peaks consistent with the presence of discrete populations of hair cells.Conclusions: The presence of distinct patterns of the ECochG response with relationships to pre-operative hearing levels supports the notion that ECochG across the electrode array functions as a measure of cochlear health.
Highlights
Cochlear implants (CIs) are no longer restricted to individuals with severe-to-profound hearing loss
A frequencyfollowing hair cell response known as the cochlear microphonic (CM) is derived by taking the difference of the two alternating responses (DIF) (Ruben et al, 1961; Dallos, 1973; Patuzzi et al, 1989)
Electrocochleography could be recorded across the electrode array in response to 0.5-kHz tone in all but six participants, in whom there was no detectable ECochG response on any electrode
Summary
Cochlear implants (CIs) are no longer restricted to individuals with severe-to-profound hearing loss. Characterizing Electrocochleography been hampered by the absence of methods to map the function of neurosensory elements along the cochlea Such a map would identify frequencies that are appropriate for acoustic stimulation and those that require electrical stimulation, identified as an important factor in the success of this combined delivery method (Gantz and Turner, 2004). ECochG has recently become available using intra-cochlear electrodes in CI recipients (Calloway et al, 2014; Campbell et al, 2015; Dalbert et al, 2015). It is a cochlear potential derived from neural and sensory sources in response to transient acoustic stimuli presented with alternating polarity. While the SUM trace is dominated by the ANN, at the high sound intensities required for ECochG in CI recipients this response may include some hair cell activity due to asymmetric saturation in the input-output function of the hair cell response (Teich et al, 1989)
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