Importance of cochlear health for cochlear-implant function

Abstract

In humans with cochlear implants, functional measures show considerable variation from one stimulation site to another along the electrode array. Our research has demonstrated that (1) the across-site patterns of the functional data are stable over time but differ across subjects; and (2) the across-site patterns are measure specific. These observations are consistent with the hypotheses that implant performance at a given stimulation site is dependent on specific conditions near the site, and that the various functional measures do not all depend on the same conditions. However, we lack direct evidence as to the specific conditions leading to the site-specific differences in performance in humans. Studies in our guinea pig laboratory and elsewhere have demonstrated highly significant correlations between psychophysical or electrophysiological measures of implant function and anatomical measures of cochlear health. Furthermore, the correlated anatomical features differ across functional measures. Finally, some functional measures that are correlated with anatomical measures of cochlear health in animals are predictive of speech recognition ability in human implant users. The data support efforts to preserve and/or restore the health of the implanted cochlea. [This work was supported by NIH/NIDCD grants R01 DC010786, R01 DC010412, and P30 DC05188, and a contract from MED-EL.]

Insertion trauma and recovery of function after cochlear implantation: Evidence from objective functional measures

“…The impairment peaked around 5 to 9 days after implant insertion, consistent with a model in which an inflammatory reaction grows over time and then dissipates. Several previous studies have shown that the slopes of amplitude-growth functions of electrophysiological potentials in response to electrical stimulation are correlated with the number of surviving auditory neurons (Smith and Simmons, 1983; Hall, 1990; Pfingst et al, 2014). It is unlikely that the number of SGNs decreased and then increased following implant insertion.…”

Multidimensional Timbre Spaces of Cochlear Implant Vocoded and Non-vocoded Synthetic Female Singing Voices

“…Further, listener factors may limit perception. These listener factors include: (a) variable patterns of nerve survival; (b) electrode array position; and (c) residual acoustic hearing (Bierer and Faulkner, 2010;Limb and Roy, 2014;Pfingst et al, 2015). At the central processing level, there may be extensive changes in the brain as a result of auditory deprivation (Stropahl et al, 2017) as well as altered general cognitive abilities (Holden et al, 2013;Kramer et al, 2018).…”

Concomitant differentiation of a population of mouse embryonic stem cells into neuron‐like cells and schwann cell–like cells in a slow‐flow microfluidic device

“…The inner ear's spiral ganglion's myelinated bipolar neurons (SGNs) provide the conduit for sensory messages from peripheral sensory receptors of mechanosensory hair cells to the central neurons in auditory brain stem nuclei. When the hair cells in the organ of Corti are lost or incapacitated, due to injury, aging, or loss of function resulting from genetic disorders, SGNs lose their peripheral targets and can progressively degenerate, so that the remaining neurons are less capable of functional interaction with either the remaining sensory organ of Corti hair cells or with a cochlear implant/prosthesis (Pfingst et al, , review). Although SGN loss in humans is less pronounced than in animal models of hair cell loss or knockout mouse models of hair cell loss (Bermingham‐McDonogh and Rubel, ; Bodmer, ; Breuskin et al, ), it appears that even if SGNs remain as long as 40 years post‐onset of deafness, their functionality can be impaired (Sato et al, ; Wise et al, ; Jiang et al, ).…”

“…To improve the performance of cochlear implants, a variety of different strategies to improve hearing perception are being tested, including advanced engineering of cochlear implant devices, which can communicate well with the brain stem (Pfingst et al, , review); cell‐replacement therapies, involving various types of stem cells to augment or substitute for lost or malfunctioning neurons (Corrales et al, ; Coleman et al, : Reyes et al, ; Chen et al, ); regrowing spiral ganglion neuronal processes to improve connections with the implant and concomitantly reduce the distance between them (Altschuler et al, ); “classical” neurotrophin‐releasing Schwann cells used to “coat” cochlear implants have been shown to enhance neurite contacts with the devices (O'Leary et al, ).…”

“…To restore hearing function and prolong survival of existing SGNs, some researchers have developed paradigms in which a single neurotrophin or a cocktail of neurotrophins was administered to deafened animals using mini osmotic pumps or via cochlear implants coated with various gels/hydrogels that can slowly release such neurotrophins (Winter et al, 2007;Jun et al, 2008;Winter et al, 2008;Jhaveri et al, 2009). However, such treatment options have not yet progressed to clinical or even preclinical trials in patients with hearing loss (Miller et al, 2002;Pettingill et al, 2007;O'Leary et al, 2009;Pfingst et al, 2015).…”