Spatial distribution of gravity-dependent gain changes in the vestibuloocular reflex

Area of Science:

• Neuroscience
• Vestibular System
• Motor Control

Background:

• The angular vestibuloocular reflex (aVOR) stabilizes gaze during head movements.
• Adaptation of the aVOR is crucial for maintaining clear vision.
• Previous studies suggested gravity's influence on aVOR adaptation, but in a limited, two-dimensional context.

Purpose of the Study:

• To investigate the three-dimensional dependence of angular vestibuloocular reflex (aVOR) gain adaptation on gravity.
• To determine if gravity's influence on aVOR adaptation is a fundamental property in three dimensions.
• To develop a conceptual framework for understanding aVOR plasticity in three-dimensional space.

Main Methods:

• Adaptation of horizontal aVOR gain in cynomolgus monkeys across various head positions (upright, side down, prone, supine).
• Testing of aVOR gains in darkness during yaw rotation with diverse head orientations.
• Mathematical modeling using sinusoidal functions to quantify gravity-dependent and independent components of gain changes.

Main Results:

• aVOR gain changes were maximal at the adapted head position and decreased with deviation.
• Both gravity-dependent (amplitude) and gravity-independent (bias) components of gain changes were approximately 25%.
• A three-dimensional surface model of aVOR gain changes qualitatively matched experimental data.

Conclusions:

• aVOR gain adaptation exhibits a significant dependence on head position relative to gravity in three dimensions.
• aVOR plasticity comprises gravity-dependent and gravity-independent components.
• Gravitational dependence likely optimizes retinal image stability during complex movements.