Identifying Cochlear Implant Channels With Relatively Poor Electrode-Neuron Interfaces Using the Electrically Evoked...

Area of Science:

• Audiology and Hearing Research
• Biomedical Engineering
• Neuroscience

Background:

• The electrode-neuron interface (ENI) is critical for cochlear implant (CI) efficacy.
• Variability in ENI quality can occur both within an individual ear and between ears.
• Age-related changes in spiral ganglion neuron (SGN) density may impact ENI quality in CI users.

Purpose of the Study:

• To quantify local (within-ear) and global (between-ear) variations in CI ENI quality.
• To assess if electrically evoked compound action potential (ECAP) measures can identify ENI quality differences.
• To investigate age-related differences in ENI quality between younger and older CI listeners.

Main Methods:

• ECAP measurements (amplitude, amplitude growth function slope, thresholds) were collected from 18 implanted ears across 13 participants (ages 14-88).
• Auditory detection thresholds were measured using a steered quadrupolar configuration.
• ECAP responses were compared between high- and low-threshold channels and between younger and older listener groups.

Main Results:

• Channels with higher behavioral thresholds (poorer ENI) exhibited steeper ECAP amplitude growth function slopes, smaller dynamic ranges, and higher ECAP thresholds.
• Younger CI listeners demonstrated steeper ECAP amplitude growth function slopes and larger ECAP peak amplitudes compared to older listeners.
• Younger listeners showed greater interphase gap sensitivity in ECAP amplitude than older listeners.

Conclusions:

• ECAP responses effectively quantify local and global ENI quality variations in CI users.
• ECAP measures show promise for optimizing CI programming strategies, particularly for site selection.
• Findings suggest younger CI users may have denser functional SGN populations, supporting age-related differences in neural integrity.