# Optimization of Stimulus Protocols for a Vestibular Implant

> **NIH NIH F31** · JOHNS HOPKINS UNIVERSITY · 2022 · $46,752

## Abstract

Project Summary – Abstract
Bilateral vestibular hypofunction (BVH) is a debilitating disorder caused by ototoxic drugs or other injuries to
the inner ear that result in dizziness, imbalance, fatigue, difficulty stabilizing gaze, and decreased quality of life.
It severely afflicts ~1.8M adults worldwide. Vestibular rehabilitation helps some individuals with BVH
compensate for their symptoms but normal function is never restored and it is not effective for all patients.
Electrical stimulation with a vestibular implant has shown promise as a viable treatment for these individuals
with severe loss. Results from one study aiming to show efficacy and safety indicate that increasing stimulus
current results in larger vestibulo-ocular reflex (VOR) responses and these eye movements are approximately
aligned with the anatomical axis of the target canal. However, it is unclear why the reported VOR responses
are modest in comparison to results from previous studies in animals, not all subjects have well aligned
responses, and eye movements can be somewhat disconjugate. The present study aims to better understand
the root of these discrepancies by investigating the effect of various stimulus paradigms on 3D VOR and
vestibular afferents. Published studies investigating electrical stimulation via cochlear or vestibular implants
have typically used symmetric pulse waveforms. However, some studies reported a significant improvement in
human cochlear implant users’ auditory thresholds when using asymmetric pulses. It is hypothesized that a
similar effect will occur in the context of vestibular implant stimulation. To quantify how VOR responses
depend on stimulus waveform parameters in alert rhesus macaque monkeys, asymmetric vestibular
implant parameters will be systematically varied while recording VOR responses. This will involve initially
testing pulses with a constant cathodic first phase, then varying the cathodic first phase duration, and finally
using an anodic first phase all while varying the interphase gap and second phase duration. Additionally, the
field of clinical vestibular implantation assumes 3D VOR magnitude and axis reflect relative activity in each of
the three semicircular canal nerve branches while ignoring the utricle and saccule. A study using finite element
modeling has predicted that prosthetic currents meant to stimulate a semicircular canal usually also activate
utricular and/or saccular neurons, and the authors speculate that such activity would elicit disconjugate VOR
responses. To understand the correspondence between monkey vestibular afferent activity and 3-D
VOR, this study also aims to record directly from individual afferents while electrically stimulating and
compare the activity to VOR responses. We will use afferent recordings to quantify the spread of current,
clarify utricle and saccule afferent activation, and understand afferent responses to asymmetric stimuli and
their correlation to VOR. From this work, we can dictate c...

## Key facts

- **NIH application ID:** 10535429
- **Project number:** 5F31DC019861-02
- **Recipient organization:** JOHNS HOPKINS UNIVERSITY
- **Principal Investigator:** Brian Morris
- **Activity code:** F31 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2022
- **Award amount:** $46,752
- **Award type:** 5
- **Project period:** 2021-07-01 → 2023-06-30

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/10535429

## Citation

> US National Institutes of Health, RePORTER application 10535429, Optimization of Stimulus Protocols for a Vestibular Implant (5F31DC019861-02). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/10535429. Licensed CC0.

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