Sensory substitution devices for bilateral vestibular loss

Timothy C. Hain, MD • Last revision: March 20, 2021

When a sense breaks down, it is quite reasonable to attempt to substitute other senses. At this writing, there are several approaches that have been tried, but none of them work well enough for most people to adopt them. The purpose of this page is to review the current state of the art for these devices. The devices that we will review are in the following categories.

In the long run, it seems to us that hair cell regeneration is the most likely to succeed route for recovery from gentamicin ototoxicity. Sensory substitution, using non-vestibular input such as vibrotactile, seems tous to be the most likely route for amelioration of vestibular nerve injury.

Galvanic stimulation

It has been suggested that external electrical current might be used to substitute for loss of inner ear function. (Scinicariello, Eaton et al. 2001; Orlov, Stolbkov et al. 2008). At the present writing, these efforts have not been translated into a usable device. Logically, it would seem difficult to imagine that a disorganized mass current flow from an external electrode could substitute for a spatially separate input from each semicircular canal. 

Perhap a "hybrid" device with a set of electrodes in a mastoid cavity combined with an external stimulator would be worth trying however.

Auditory stimulation

It seems reasonable that auditory input might be used to assist with balance. Some effort has been made (Lee, Wong et al. 1996; Wong, Mak et al. 2001; Dozza, Chiari et al. 2004; Dozza, Chiari et al. 2005; Dozza, Chiari et al. 2006; Dozza, Horak et al. 2007; Ernst, Singbartl et al. 2007; Basta, Singbartl et al. 2008.

This direction seems reasonable to us and we hope that commercial devices emerge.

Vestibular implant

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).

Brainport

Tongue Input (TDU) or "brainport" device

In a bizarre twist , there have been efforts to replace vestibular input using a tongue stimulator. (Tyler, Danilov et al. 2003; Danilov, Tyler et al. 2006; Danilov, Tyler et al. 2007; Vuillerme, Chenu et al. 2008; Vuillerme and Cuisinier 2008; Uneri and Polat 2009; Vuillerme and Cuisinier 2009; Wood, Black et al. 2009). Imagine --going around with a head-mounted paddle on your tongue ! Follow the TDU link for more details.

Vibrotactile input

It is somewhat reasonable that vibration input to the body might substitute for vestibular input, and again there has been considerable work done here. (Mackenzie, McCracken et al. 1997; Rochlis and Newman 2000; Kentala, Vivas et al. 2003; Nagel, Carl et al. 2005; Wall and Kentala 2005; Peterka, Wall et al. 2006; Asseman, Bronstein et al. 2007; Dozza, Wall et al. 2007; Basta and Ernst 2008; Guzy, Albery et al. 2008; Sienko, Balkwill et al. 2008; Goebel, Sinks et al. 2009; Horak 2009; Horak, Dozza et al. 2009)

We think that this direction is presently the most logical one

References regarding galvanic input

References for auditory input

References regarding vestibular prostheses

References regarding tongue input -- also see (TDU)

References regarding vibrotactile input