Directional plasticity rapidly improves 3D vestibulo-ocular reflex alignment in monkeys using a multichannel...

Area of Science:

• Neuroscience
• Biomedical Engineering
• Ophthalmology

Background:

• Bilateral loss of vestibular sensation causes significant disability.
• A multichannel vestibular prosthesis (MVP) shows promise in restoring vestibular sensation and improving the 3-dimensional angular vestibulo-ocular reflex (3D VOR).
• Minimizing misalignment between eye and head rotation axes is crucial for MVP efficacy, potentially caused by electrical current spread.

Purpose of the Study:

• To investigate if rhesus monkeys exhibit adaptive improvements in 3D VOR alignment with continuous MVP stimulation over time.
• To assess the time course of adaptation and the extent of VOR axis realignment in response to prosthetic vestibular input.

Main Methods:

• Four rhesus monkeys with experimentally induced bilateral vestibular deficiency were fitted with a MVP.
• 3D VOR responses to passive whole-body rotations were measured before and after one week of continuous, head motion-modulated MVP stimulation.
• Measurements were taken on days 1, 3, and 7 of stimulation across various rotation frequencies and accelerations.

Main Results:

• Initial MVP activation (Day 1) showed improved VOR gain but significant axis misalignment (30-40°).
• After 7 days of continuous stimulation, substantial improvement in VOR axis alignment was observed across all tested rotation parameters and animals.
• While VOR gain improved, changes in VOR asymmetry were not statistically significant but trended towards improvement.

Conclusions:

• Rhesus monkeys demonstrate rapid adaptation to a MVP, significantly improving 3D VOR alignment despite initial sensory misorientation.
• This study confirms that the central nervous system can adapt to misoriented vestibular input, restoring a well-aligned 3D VOR, analogous to visual adaptation.
• Findings suggest that humans with bilateral vestibular deficiency using an MVP may experience similar adaptive benefits, paving the way for improved rehabilitation strategies.