The Effect of Aging on Auditory Nerve Function: Insights from Intraoperative eCAP Recordings in Cochlear Implant Users

Abstract

Background Advanced age is associated with poorer speech perception outcomes in cochlear implant (CI) users. In an effort to improve our understanding of the basis for this decline, this study focused on the contributions from peripheral auditory processing, using the electrically evoked compound action potential (eCAP). Objectives To investigate the effect of aging on intraoperative, suprathreshold eCAP responses (amplitude growth function [AGF] slopes, eCAP maximum amplitudes, and N1 latencies) across the electrode array, in a large cohort of recipients of newer generation devices, who met hearing preservation criteria. Methods Participants of this retrospective study consisted of 113 middle-aged and older CI recipients. Intraoperative eCAP measures consisted of AGF slopes, maximum amplitudes, and N1 latencies at the maximum amplitude. eCAP recordings were obtained at several intracochlear electrodes, which were grouped by electrode location (basal, middle, and apical). Results There was a moderate to strong association between suprathreshold eCAP measures (eCAP AGF slopes and maximum amplitudes) and age, particularly for basal and middle electrodes. For apical electrodes, correlations between both suprathreshold eCAP measures and age were weak (and for eCAP maximum amplitudes, not statistically significant). N1 latencies at the maximum amplitudes were not associated with age at any electrode location. Conclusions Results of this study add to a growing body of evidence suggesting that aging may negatively affect suprathreshold eCAP responses, especially in basal and middle cochlear regions. Although it is difficult to separate the effects of aging from those of duration of deafness, both would support recommending early implantation in the clinical setting.