Unilateral deafferentation and eye position misdirect the initial vestibulo-ocular reflex: a model-based study

Area of Science:

• Neuroscience
• Vestibular System Research
• Ophthalmology

Background:

• The vestibulo-ocular reflex (VOR) stabilizes gaze during head movements.
• VOR axis direction is influenced by both eye position and vestibular sensitivity.
• Unilateral vestibular deafferentation (UVD) disrupts normal vestibular function.

Purpose of the Study:

• To investigate the interaction between orbital eye position and vestibular sensitivity in determining VOR axis direction in individuals with UVD.
• To quantify VOR axis deviations in response to transient head rotations in normal subjects and those with UVD.

Main Methods:

• Measured VOR direction and magnitude in response to high-acceleration yaw rotations.
• Assessed the effect of eye position using the tilt angle ratio (TAR) for upward and downward targets.
• Compared responses between six normal subjects and five subjects with UVD.

Main Results:

• UVD subjects showed reduced VOR gain during ipsilesional rotation compared to contralesional rotation and normal controls.
• A significant initial forward VOR axis tilt was observed in UVD subjects during ipsilesional rotation.
• The tilt angle ratio (TAR) in UVD subjects indicated a compromise between Listing's Law and head-aligned VOR, suggesting canal nonlinearity and geometric orientation contribute to VOR error.

Conclusions:

• A vector-based model explains VOR axis tilt in UVD, attributing it to semicircular canal properties rather than eye position effects.
• Canal nonlinearity and geometric orientation are key factors in the observed VOR axis errors following UVD.
• Late visual pursuit synergy may influence VOR responses in UVD subjects between 150-200 ms post-rotation.