Timothy C. Hain, MD • Last revision: September 29, 2022
See also: bilateral vestibular loss•gentamicin_toxicity•natural history• galvanic stimulation• regeneration • sensory_substitution
As cochlear implants can sometimes restore hearing, why shouldn't vestibular implants be also possible ? Many papers have been published on this topic (Gong and Merfeld 2000; Gong and Merfeld 2002; Lewis, Gong et al. 2002; Ciaravella, Laschi et al. 2006; Merfeld, Gong et al. 2006; Shkel and Zeng 2006; Della Santina, Migliaccio et al. 2007; Wall, Kos et al. 2007; Tang, Melvin et al. 2009; Della Santina et al, 2010; Dai et al, 2011; Boutros et al, 2019; Chow et al, 2021).
Guyot et al (2011) showed in 3 humans undergoing surgery for Meniere's disease that stimulation of the lateral and superior ampullary nerve is possible using an operative approach where the ossicles were removed, and a electrode was placed in a "small well was drilled above the horizontal portion of the facial nerve canal". A predominantly horizontal nystagmus was provoked.
In our opinion, vestibular implants are still experimental and there are major obstacles to overcome. While the cochlear spiral ganglion is spread out in an organized spiral, the nerves to the three semicircular canals are not easily accessible. For example, in the report above by Guyot, stimulation was obtained by sacrificing hearing, and the eye movements were not purely horizontal. More recent reports (e.g. Chow et al, 2021) also encountered reduction of hearing. The otolith organs, which sense linear acceleration, are not stimulated with this approach.
As of 2021, there is a report of outcomes of vestibular implant (for the canals) in 7 patients who had undergone ototoxicity. Generally there was improvement. They stated "Six months and 1 year after unilateral implantation of a vestibular prosthesis for bilateral vestibular hypofunction, measures of posture, gait, and quality of life were generally in the direction of improvement from baseline, but hearing was reduced in the ear with the implant in all but 1 participant." (Chow et al, 2021)
In an earlier publication from the same group, it was reported that "a vestibular implant can selectively, continuously, and chronically provide artificial sensory input to all 3 implanted semicircular canals in individuals disabled by bilateral vestibular loss, driving reflexive VOR eye movements that approximately align in 3D with the head motion axis encoded by the implant." (Boutros et al, 2019).