Progress Toward Development of a Multichannel Vestibular Prosthesis for Treatment of Bilateral Vestibular Deficiency

Abstract

This article reviews vestibular pathology and the requirements and progress made in the design and construction of a vestibular prosthesis. Bilateral loss of vestibular sensation is disabling. When vestibular hair cells are injured by ototoxic medications or other insults to the labyrinth, the resulting loss of sensory input disrupts vestibulo-ocular reflexes (VORs) and vestibulo-spinal reflexes that normally stabilize the eyes and body. Affected individuals suffer poor vision during head movement, postural instability, chronic disequilibrium, and cognitive distraction. Although most individuals with residual sensation compensate for their loss over time, others fail to do so and have no adequate treatment options. A vestibular prosthesis analogous to cochlear implants but designed to modulate vestibular nerve activity during head movement should improve quality of life for these chronically dizzy individuals. We describe the impact of bilateral loss of vestibular sensation, animal studies supporting feasibility of prosthetic vestibular stimulation, the current status of multichannel vestibular sensory replacement prosthesis development, and challenges to successfully realizing this approach in clinical practice. In bilaterally vestibular-deficient rodents and rhesus monkeys, the Johns Hopkins multichannel vestibular prosthesis (MVP) partially restores the three-dimensional (3D) VOR for head rotations about any axis. Attempts at prosthetic vestibular stimulation of humans have not yet included the 3D eye movement assays necessary to accurately evaluate VOR alignment, but these initial forays have revealed responses that are otherwise comparable to observations in animals. Current efforts now focus on refining electrode design and surgical technique to enhance stimulus selectivity and preserve cochlear function, optimizing stimulus protocols to improve dynamic range and reduce excitation–inhibition asymmetry, and adapting laboratory MVP prototypes into devices appropriate for use in clinical trials.

Prevalence and Impact of Bilateral Vestibular Hypofunction

“…Furthermore, some BVH subjects never adequately recover performance, as can be demonstrated in the functional impairments seen in many respondents in this and other studies 17 . Attempts to replace vestibular sensation with tactile stimulation of the torso, sound, and electrical stimulation of the tongue have identified postural effects, but are unlikely to improve VOR function 24 . In contrast, implantable vestibular prostheses may help patients with BVH recover VOR function (reviewed in references 34 and 35) 24, 25 .…”

Longitudinal performance of an implantable vestibular prosthesis

“…For this reason, if there is a permanent loss of hair cell function, there is also a permanent loss of natural sensory input to the vestibular system. One strategy for treating hair cell loss is to bypass the missing receptor cells using direct electrical stimulation of the nerves innervating each end organ (Golub et al, 2010, 2013; Fridman and Della Santina, 2012; Merfeld and Lewis, 2012). This strategy has already achieved remarkable success for treating hair cell loss in another comparable sensory modality, hearing, with cochlear implants.…”

“…Much research effort by multiple groups has been spent on the development of an implantable single and multichannel vestibular neurostimulator over the past two decades (Fridman & Della Santina, 2012; Chiang et al, 2011; Cohen et al, 1964; Cohen and Suzuki, 1963; Bierer et al, 2012; Dai et al, 2011b,c, 2013; Davidovics et al, 2011, 2013; Della Santina et al, 2005, 2007; Fridman et al, 2010; Gong and Merfeld, 2000, 2002; Gong et al, 2008; Lewis et al, 2001, 2002, 2010, 2013; Merfeld et al, 2006, 2007; Nie et al, 2011, 2013; Phillips et al, 2011; Rubinstein et al, 2012; Sun et al, 2011; Suzuki and Cohen, 1964, Thompson et al, 2013; Valentin et al, 2013; Phillips et al, 2013; Golub et al, 2013; Perez Fornos et al, 2014; Guyot et al, 2011a, b, 2012; Wall et al, 2007; Van de Berg et al, 2012). The studies have described the efficacy of these devices in driving vestibulo-ocular reflex (VOR) mediated eye movements with electrical stimulation in a range of species, including humans.…”

Bilateral Vestibular Hypofunction: Challenges in Establishing the Diagnosis in Adults

“…Once established, BVH could be classified according to severity, taking not only objective measures but also functional impairment into account. A classification according to severity could be important, since much progress has been made in developing a vestibular implant [144,166,167,168] and such a classification could facilitate patient selection. If necessary, a subdivision into probability groups (e.g.…”