Spatial Orientation, Navigation, and Neuropsychologic Function in Patients With Vestibular Implant

This project will test the capability of a vestibular implant (VI) to improve cognitive dysfunction in patients with severe vestibular damage. At Mass Eye and Ear (MEE), we will test non-implant vestibular patients with differing degrees of vestibular damage. At the University of Geneva (UNIGE), they will recruit and implant patients with severe vestibular and auditory deficits with a combined cochlear and vestibular implant. These are the patients with VIs we intend to test in collaboration with the UNIGE team. Notably, all implant surgeries are done at UNIGE as part of their ongoing vestibular implant research. The team at MEE submitting this CT.gov study is not involved with any aspect of the recruitment, surgery, or post-operative care of the patients receiving implants at UNIGE. We will work with the team at UNIGE to study these patients after they have received the VI on the protocols described below before, during, and after they receive stimulation from the VI. Specifically, we will measure how higher-level behaviors, including spatial orientation, navigation, and neuropsychologic function, are affected by stimulation provided by the vestibular implant, and in parallel will study these behaviors in non-implanted patients with different degrees of vestibular impairment. Our goal is to determine if the cognitive dysfunction experienced by patients with severe vestibular damage can be improved with prosthetic stimulation, findings which would expand the clinical utility of the vestibular implant while concomitantly improving understanding of the role of vestibular information in cognition. Damage to the vestibular periphery is typically permanent and untreatable (aside from physical therapy), and when it is bilateral, can result in severe degradation of vestibular-dependent behaviors. The VI was developed as a vestibular analogue to the widely employed cochlear implant, senses the head's angular velocity in three-dimensions, and provides this information to the brain by stimulating semicircular canal afferents using implanted electrodes. While VI research has progressed from animal models to human patients with vestibular damage, it has focused almost exclusively on eye movements and to a lesser extent balance and gait (although recent human studies also queried subjective measures of dizziness and quality of life). Cognitive processes have been ignored in prior VI studies, even though cognitive symptoms (often referred to as "brain fog") can be prominent and disabling in vestibular-deficient patients. More generally, vestibular contributions to cognition remain controversial and poorly characterized. In this study, we will investigate the effects of VI stimulation on (1) spatial orientation, (2) navigation, and (3) neuropsychologic function by characterizing these behaviors in patients with bilateral vestibular loss (BVL) who have unilateral VIs, with and without chronic vestibular stimulation. To serve as benchmarks for the BVL patients with/without VI stimulation, and to define the effects of vestibular loss on cognitive behavior, we will also study non-implanted BVL and unilateral vestibular loss (UVL) patients and normal subjects. Subjective assessments of cognitive function, dizziness and perceived disability will be also be measured using patient reported outcome measures (PROMs) and we will also assess more general quality-of-life metrics. We predict that the VI will improve spatial orientation, navigation, and visuo-spatial neuropsychologic function in BVL patients and that these measures will display correlations with the PROMs that characterize symptom severity and quality-of-life metrics. In sum, the proposed work will be the first to examine the capability of chronic VI stimulation to improve the cognitive deficits caused by severe vestibular damage, and will also examine the association between the severity of vestibular damage and the degree of cognitive deficits, and the relationship between vestibular-mediated cognitive deficits and the metrics that quantify subjective disability. This work will advance scientific knowledge while promoting the development of the VI as a therapy that has the potential to improve the clinical status and quality-of-life for vestibular-deficient patients.

• vestibular implant stimulation (Device): Two types of stimulation are used, tonic + motion-modulated ("true") \& tonic-only ("placebo") stimulation; order is randomized. The VI stimulation period prior to testing is 12 days. For the experiments, the VI is connected to the head-mounted prosthetic circuit and then stimulation is activated. The stimulation unit is the current-balanced biphasic pulse, and the pulse amplitude for each subject is determined through a tuning procedure. Experiments start with an adaptation to tonic baseline stimulation with the head stationary (\~30 min). Motion-modulated stimulation employs 3 angular velocity sensors (one aligned with the sensitive axis of each canal), the transduced head velocity signal is high-pass filtered to simulate normal canal dynamics, and filtered head velocity is used to modulate the strength (magnitude, rate) of the electrical stimulation provided by the corresponding implanted electrode. Stimulation strength adjusts for head rotations that change canal afference.

Primary outcomes

• Spatial Orientation: Changes in Subjective Postural Vertical [pre-stim, chronic stim (1month + 12 days), and post-stim (1month)]: Spatial orientation (subjective postural vertical) results are assessed for their accuracy and precision. Tests are repeated to look at changes for pre-stimulation (VI-OFF), following chronic stimulation (VI-ON), and post-stimulation (VI-OFF).
• Spatial Orientation: Changes in Roll Tilt Perceptual Thresholds [pre-stim, chronic stim (1month + 12 days), and post-stim (1month)]: Spatial orientation (roll tilt perceptual thresholds) results are assessed for their accuracy and precision. Tests are repeated to look at changes for pre-stimulation (VI-OFF), following chronic stimulation (VI-ON), and post-stimulation (VI-OFF).
• Changes in Navigation [pre-stim, chronic stim (1month + 12 days), and post-stim (1month)]: Navigation in a virtual reality visual environment is tested using a 'complete the triangle' task and results are assessed for their accuracy and precision. Tests are repeated to look at changes for pre-stimulation (VI-OFF), following chronic stimulation (VI-ON), and post-stimulation (VI-OFF).
• Changes in Neuropsychologic Function [pre-stim, chronic stim (1month + 12 days), and post-stim (1month)]: Visuospatial and non-visuospatial neuropsychologic function are assessed using a standard battery of neuropsychologic tests. Tests are repeated to look at changes for pre-stimulation (VI-OFF), following chronic stimulation (VI-ON), and post-stimulation (VI-OFF).

Sex: All, ages: 18 Years to 80 Years

1. Patients receiving vestibular implants at UNIGE:

   Their inclusion criteria are defined as follows:
   * Deaf, scheduled for CI surgery
   * Minimum of five year history of documented absence of bilateral auditory and vestibular function, based on review of their audiograms and vestibular tests.
   * Vestibular testing consistent with BVL
   * No neurologic disease. note: these patients are recruited and implanted by the group at the University of Geneva Hospital (UNIGE) as part of their ongoing research. The study team are not involved in any way with the decision to surgically implant patients with cochlear or vestibular implants, nor are the researchers involved in any way with pre- or post-operative clinical care. The researchers only involvement is to perform the cognitive tests before, during, and after relatively short periods of stimulation using the vestibular implant (VI)
2. Vestibular patients tested at MEE: vestibular testing consistent with unilateral or bilateral vestibular damage.

Both aspects of the study share the same exclusion criteria:

Exclusion Criteria:

* No known neurologic or otologic disease other than the vestibular and auditory deficits noted above.
* Pregnancy. Pregnant women and women up to 4 months postpartum will be excluded because of the known effects and unknown potential effects of pregnancy on sensory function.
* Body weight >250 lbs (due to motion device safety limits)
* The chronic use of vestibular suppressant medication (benzodiazepine, antihistamine, anticholinergic)
* Inability to stand or walk unassisted.
* Blindness.
* Unstable medical condition.
* Orthopedic or musculoskeletal injuries/conditions that affect gait or balance.
* Ongoing neck or spinal pain/injuries or recent history of neck or spinal surgery
* Amputation, musculoskeletal deformity, or significant leg-length discrepancy
* A history of severe head trauma.
* Any major psychiatric disorder (e.g., psychosis, schizophrenia, panic disorder), not including anxiety or depression.
* Severe heart or pulmonary conditions
* Active cancer for which chemo-/radiation therapy is being received.

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NIH grants: R01DC021981