Peripheral Neural Plasticity in Cochlear Implant Users Across the Lifespan.

Importance: Neural recordings from cochlear implant users provide a valuable, noninvasive measure of auditory nerve function. However, inconsistent methods for acquiring and analyzing these recordings limit their clinical application. Objective: To develop and validate an automated method for standardizing the analysis of electrically evoked compound action potentials in cochlear implant users, and to characterize longitudinal changes in auditory nerve function across the largest cohort studied to date. Design, Settings, and Participants: This multicenter cohort study used nonlinear curve-fitting models to analyze electrically evoked compound action potentials acquired during clinical programming and follow-up at multiple US centers from July 28, 2002, to August 13, 2017. Data were analyzed from October 8, 2024 to May 6, 2025. Main Outcomes and Measures: Model fit success rates; variation in auditory nerve response parameters with age, sex, electrode location, and duration of implant use; and identification of age-related periods of peripheral neural plasticity. Results: The analysis included 1 145 323 electrically evoked compound action potential recordings comprising 169 159 growth functions from 10 111 cochlear implants in 7416 patients (3560 [48%] female and 3856 [52%] male individuals). Both models successfully fit approximately 80% of auditory-nerve growth functions. Thresholds increased from apex to base along the cochlear array, paralleled by a decline in response slope and plateau. Latencies remained stable across electrode locations. Age at implantation significantly predicted nerve response slope, with younger recipients showing steeper slopes that declined with increasing age, particularly after adolescence. In infants and toddlers, slopes continued to increase over 5 years of implant use, suggesting peripheral neural plasticity early in life. Older recipients showed minimal slope change over time. Although thresholds rose modestly with prolonged device use, slope and plateau stabilized after age 30 years, indicating that age at implantation, rather than stimulation duration, was the primary determinant of auditory nerve responsiveness. Conclusions and Relevance: This cohort study introduces a robust and scalable framework for in vivo assessment of auditory nerve function and monitoring of peripheral plasticity across the lifespan. The findings highlight the critical importance of early cochlear implantation for preserving neural health and optimizing long-term outcomes.