Multichannel Vestibular Prosthesis Employing Modulation of Pulse Rate and Current with Alignment Precompensation Elicits Improved VOR Performance in Monkeys
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An implantable prosthesis that stimulates vestibular nerve branches to restore the sensation of head rotation and the three-dimensional (3D) vestibular ocular reflex (VOR) could benefit individuals disabled by bilateral loss of vestibular sensation. Our group has developed a vestibular prosthesis that partly restores normal function in animals by delivering biphasic current pulses via electrodes implanted in semicircular canals. Despite otherwise promising results, this approach has been limited by insufficient velocity of VOR response to head movements that should inhibit the implanted labyrinth and by misalignment between direction of head motion and prosthetically elicited VOR. We report that significantly larger VOR eye velocities in the inhibitory direction can be elicited by adapting a monkey to elevated baseline stimulation rate and current prior to stimulus modulation and then concurrently modulating (“co-modulating”) both rate and current below baseline levels to encode inhibitory angular head velocity. Co-modulation of pulse rate and current amplitude above baseline can also elicit larger VOR eye responses in the excitatory direction than do either pulse rate modulation or current modulation alone. Combining these stimulation strategies with a precompensatory 3D coordinate transformation improves alignment and magnitude of evoked VOR eye responses. By demonstrating that a combination of co-modulation and precompensatory transformation strategies achieves a robust VOR response in all directions with significantly improved alignment in an animal model that closely resembles humans with vestibular loss, these findings provide a solid preclinical foundation for application of vestibular stimulation in humans.
Keywordsvestibular implant vestibular prosthesis rhesus macaque electrical stimulation precompensation co-modulation neurostimulation
The authors thank Lani Swarthout for assistance with animal care. This research was supported by the US National Institutes of Health/National Institute on Deafness and Other Communication Disorders (NIH/NIDCD) grants R01DC009255, R01DC002390 and 1F31DC010099.
Conflict of interest
CCDS and GYF are inventors on university-assigned patents related to prosthesis technology. CCDS is the founder and CEO of Labyrinth Devices, LLC, in which he holds an equity interest. The terms of this arrangement are being managed by the Johns Hopkins University in accordance with its conflict of interest policies.
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