Effects of semicircular canal electrode implantation on hearing in chinchillas

Abstract

Conclusion-Implantation of vestibular prosthesis electrodes in chinchilla semicircular canal ampullae can be accomplished without significant loss of cochlear function; however, the risk of hearing loss with the current surgical technique is high.Objectives-To determine if it is possible to implant vestibular prosthesis electrodes into the labyrinth without damaging hearing, and to quantify the extent of hearing loss due to implantation.Method-The left semicircular canals of 6 chinchillas were implanted with 3 bipolar pairs of electrodes using a transmastoid approach. Right ears, which served as controls, were subjected to the same mastoid approach without fenestration and implantation. Auditory brainstem response hearing thresholds to free field clicks and tone pips at 2, 4, 6, and 8 kHz were measured bilaterally 3-9 weeks after implantation. Hearing thresholds were compared between sides and against data from 6 normal chinchillas.Results-4 implanted ears suffered severe hearing loss, with thresholds ranging from 5 to 11 SD above the mean threshold of sham surgery control ears across all tested stimuli. 2 implanted ears had preserved hearing, with thresholds remaining within 1 SD of the mean threshold of sham surgery control ears across nearly all stimulus frequencies.

Vestibular Implants: 8 Years of Experience with Electrical Stimulation of the Vestibular Nerve in 11 Patients with Bilateral Vestibular Loss

“…In contrast, the intralabyrinthine approach might allow better selectivity of the stimulation but the risk of inducing hearing loss in this case is still unclear. Results of animal studies are controversial: some demonstrate that intralabyrinthine electrode insertion with or without electrical stimulation impairs hearing in most of the cases [60,61,62], while others show that it is possible to preserve auditory and vestibular function [63]. The results in human patients are not very encouraging in this respect.…”

Safe Direct Current Stimulation to Expand Capabilities of Neural Prostheses

“…We therefore studied the use of DC modulation in application to prosthetic stimulation of the vestibular nerve, an application with which we have significant experience [21–36] and for which SCDS1’s ability to inhibit spontaneous activity would be especially advantageous.…”

Restoring the 3D vestibulo-ocular reflex via electrical stimulation: The Johns Hopkins multichannel vestibular prosthesis project

“…Whereas cochlear implant electrode arrays can be inserted near the auditory nerve while remaining completely in the scala tympani, implantation of electrodes near the semicircular canals’ cristae probably disrupts the membranous labyrinth. In a previous study of hearing in chinchillas undergoing vestibular electrode implantation, we found that hearing was compromised in 4 of 6 animals [12]; however, differences in size and surgical approach preclude generalization of these data to humans with certainty.…”