Assessing Longitudinal Changes In Peripheral Versus Central Processing of Newly Implanted Cochlear Implant Recipients

Abstract Cochlear implants can restore a sense of hearing to recipients with severe to profound hearing loss, but speech perception is still highly variable among recipients. After implantation, recipients take time to acclimatize to their device and speech perception generally improves over the first six months before they reach a plateau in performance. Unfortunately, the factors that determine the extent and timecourse of acclimatization are still not well understood. Therefore, we will obtain longitudinal measures at multiple levels of the auditory system over the first six months following CI activation in adults. At the periphery of the cochlear-implanted auditory system, the electrode-neuron-interface (ENI) describes how well the implant electrodes stimulate nearby auditory nerve cells. A poor ENI generally results in unwanted channel interaction and poorer overall performance, which may act as a limiting factor on the extent of acclimatization. At the higher levels of auditory processing, numerous studies have shown that cognitive factors measured before implantation are positively correlated with speech perception scores, suggesting that central processing is involved in acclimatization, or at least in speech perception once acclimatization has occurred. The goal of this project is to probe the origin of acclimatization through a series of tests that start at the periphery of the auditory system and increase in complexity and inclusion of the central auditory system. Electrically evoked compound action potentials (ECAP) can measure the synchronous response of the auditory nerve from CI electrodes in response to stimulation of a nearby electrode. The neural spread of excitation can be measured using ECAP and allows us to quantify channel interaction at the periphery. Channel interaction can also be measured perceptually through psychophysical tuning curves (PTCs), thereby passing through the ascending auditory system. Finally, the STRIPES (Spectro-Temporal Ripple for Investigating Processor EffectivenesS) test is a different, more complex measure of spectral resolution that does not use speech as a signal. Combined, these three measures and speech perception can better characterize acclimatization at varying levels of complexity over the first 6 months in newly implanted recipients. We will also determine the extent to which various cognitive factors drive or limit acclimatization when measures of ENI quality are also taken into account. If successful, these findings could help better predict performance in newly implanted recipients, which could then be used to guide recipient expectations or to identify recipients who may benefit from increased aural rehabilitation or new, alternative methods of reducing channel interaction, such as those under investigation in the Arenberg Lab.