Stimulation Crosstalk Between Cochlear And Vestibular Spaces During Cochlear Electrical Stimulation.

OBJECTIVES: Possible beneficial "crosstalk" during cochlear implant stimulation on otolith end organs has been hypothesized. The aim of this case-control study is to analyze the effect of electrical cochlear stimulation on the vestibule (otolith end-organ), when using a cochleo-vestibular implant, comparing vestibular stimulation (VI) and cochlear stimulation (CI). METHODS: Four patients with bilateral vestibulopathy were included. A double electrode array research implant was implanted in all cases. Dynamic Gait Index (DGI), VOR gain measured by using vestibular head impulse test (vHIT), acoustic cervical myogenic responses (cVEMP) recordings, and electrical cVEMP were used in all cases. Trans-impedance Matrix (TIM) analysis was used to evaluate the current flow from the cochlea to the vestibule. RESULTS: While patients did not have any clinical vestibular improvement with the CI stimulation alone, gait metrics of the patients revealed improvement when the vestibular electrode was stimulated. The average improvement in the DGI was 38% when the vestibular implant was activated, returning to the normal range in all cases. Our findings suggest that any current flow from the cochlear space to the otolith organs was insufficient for effective cross-stimulation. The functional results correlated with the data obtained in TIM analysis, confirming that there is no current flow from the cochlea to the vestibule. CONCLUSION: The only way to produce effective electrical otolith end-organ stimulation, demonstrated with this research implant, is by direct electrical stimulation of the otolith end organs. No effective cross-stimulation was found from cochlear electrode stimulation. LEVEL OF EVIDENCE: 4 Laryngoscope, 134:2349-2355, 2024.

Why Should Constant Stimulation of Saccular Afferents Modify the Posture and Gait of Patients with Bilateral Vestibular Dysfunction? The Saccular Substitution Hypothesis.

An ongoing EU Horizon 2020 Project called BionicVEST is investigating the effect of constant electrical stimulation (ES) of the inferior vestibular nerve in patients with bilateral vestibular dysfunction (BVD). The evidence is that constant ES results in improved postural stability and gait performance, and so the question of central importance concerns how constant ES of mainly saccular afferents in these BVD patients could cause this improved performance. We suggest that the constant ES substitutes for the absent saccular neural input to the vestibular nuclei and the cerebellum in these BVD patients and indirectly via these structures to other structures, which have been of great recent interest in motor control. One target area, the anterior midline cerebellum (the uvula), has recently been targeted as a location for deep-brain stimulation in human patients to improve postural stability and gait. There are projections from midline cerebellum to basal ganglia, including the striatum, which are structures involved in the initiation of gait. It may be that the effect of this activation of peripheral saccular afferent neurons is analogous to the effect of deep-brain stimulation (DBS) by electrodes in basal ganglia acting to help alleviate the symptoms of patients with Parkinson's disease.

Transcutaneous Osseo-integrated Auditory Devices: Analysis of Two Different Implants in Adults With Different Audiological Inclusion Criteria.

OBJECTIVE: To determine and compare audiological and speech/language discrimination results in patients with osteo-integrated auditory devices, by comparing two different systems including different audiological indications in adult population. STUDY DESIGN: Descriptive and analytic, cross-sectional, cohort, and retrospective case review. SETTING: Tertiary referral center. MATERIALS AND METHODS: Fifty patients >14 years old, with conductive, mixed, or unilateral sensorineural hearing loss were compared. The variables studied were the following: pure tone audiometry results, air-bone gap, and the percentage of speech/language discrimination using Disyllabic Word Test. The patients were tested preoperative and 12 months after surgical procedure. Subsequently, a comparative analysis of the both systems was carried out. RESULTS: With both implants, pure tone audiometry results and the difference in auditory thresholds and between the air-bone gap improved significantly. Speech discrimination increased significantly after implantation too. A significant difference was observed after implantation of both devices. Patients implanted with one of the implants showed better audiological results, but no significant differences were found with the other device. So, it was shown that the type of device and the type of hearing loss have no influence on the audiological results or complications. CONCLUSION: Both implants represent a good choice for audiological rehabilitation in patients with transmissive hearing loss, mixed hearing loss, or unilateral sensorineural hearing loss with a high success and low complication rates.