The Effect of Aging on the Electrically Evoked Compound Action Potential.

Objectives: To examine the effect of aging on electrically evoked compound action potential (eCAP) growth functions and their relationship with speech recognition in noise in cochlear implant (CI) users.

Background: Aging typically leads to difficulty understanding speech in background noise. Previous research has explored cognitive and central auditory mechanisms contributing to these age-related changes. However, it is likely that the peripheral auditory system may also play a role. One challenge is separating the effects of aging on cochlear structures from the effects of aging on the auditory nerve in humans. CI users provide a unique way to address this issue, as intracochlear electrical stimulation bypasses surviving hair cells and activates the auditory nerve directly. Studies in animal models suggest that age-related loss of spiral ganglion cells could lead to shallower eCAP growth functions and/or increased eCAP thresholds and potentially negatively impact speech recognition.

Methods: Ten younger and 10 older postlingually deafened, adult CI recipients participated in this study. eCAP amplitude-intensity functions were recorded from a mid-array electrode and fit using linear functions. Speech recognition in noise was assessed using the Quick Speech-in-Noise (QuickSIN) test.

Results: Older CI users had significantly shallower eCAP growth functions and higher eCAP thresholds than younger CI users. eCAP growth functions were not correlated with speech recognition in noise.

Conclusion: Results of this study suggest that older adults may have poorer neural survival, resulting in higher eCAP thresholds and shallower eCAP growth functions. These findings expand our understanding of mechanisms underlying age-related changes in the peripheral auditory system.