Investigating the Recovery Properties of Auditory Nerve Fibres at Different Cochlear Regions using Electrically Evoked Compound Action Potential

Abstract

Introduction: Investigating the recovery function and refractory properties of auditory nerve is essential for us to understand the physiology at neural level, not many tools are available to carry out research in humans. Electrically Evoked Compound Action Potential (ECAP) helps us to record the action potential and also provides us with an option of varying the Interpulse Interval (IPI), hence there is a need to carry out research in Cochlear Implant (CI) users with the help of ECAP. Aim: To investigate the refractory property of the neurons and the response characteristics at different cochlear regions. Materials and Methods: Fifty CI users from age 3-10 years with a minimum hearing experience of three months underwent ECAP measures at various IPI. The data were further statistically analysed using SPSS software version 20.0, descriptive and inferential statistics were carried out using ANOVA. Results: It was found that a high ECAP threshold (648 cu) could be found at the basal region of cochlea when compared to medial (658 cu) and apical region (785 cu) at 300 μs and similar higher thresholds at different IPI, thus attributing to the fact that with increase in population of nerve fibres, a better threshold could be achieved. Another finding revealed that with very low IPI, the ECAP thresholds were elevated, with neural recruitment being a contributing factor. Conclusion: There was a difference in neural population amongst individuals, even with better auditory performance. ECAP is one of the objective tool to measure neural function and outcomes in CI individuals.

Keywords

• auditory nerve
• cochlea
• cochlear implant
• recruitment
• refractory period