Vertical vestibuloocular reflex in cat: asymmetry and adaptation

Area of Science:

• Neuroscience
• Ophthalmology
• Vestibular System Research

Background:

• The vertical vestibulo-ocular reflex (VOR) stabilizes gaze during head movements.
• Understanding the temporal dynamics and adaptive capabilities of the VOR is crucial for explaining visual-vestibular integration.

Purpose of the Study:

• To characterize and compare the initial 2 seconds of upward and downward vertical VOR eye velocity in cats.
• To investigate the effects of VOR gain adaptation on these eye movements.
• To delineate distinct phases within the VOR response trajectory.

Main Methods:

• Cats were positioned in a 90-degree roll position and rotated about an earth-vertical axis in the dark.
• Brief trapezoidal velocity profiles were used as vestibular stimuli.
• Eye movements were recorded using a magnetic search coil, and eye velocity was analyzed with high temporal resolution.

Main Results:

• After a ~15 ms latency, peak eye velocity rapidly matched head velocity, then decayed to a plateau of approximately -0.6 times head velocity.
• Upward and downward peak eye velocities were symmetric, but the transition to plateau was faster for downward VOR, and the upward plateau was ~15% higher.
• VOR gain adaptation was symmetric, affecting plateau more than peak eye velocity, with no change in latency. The VOR trajectory showed an invariant (~15 ms) and a variant interval, with adaptation primarily influencing the variant interval.

Conclusions:

• The VOR response exhibits distinct invariant and variant intervals, suggesting separate neural processing.
• The invariant interval may reflect the direct three-neuron arc, while the variant interval is modulated by adaptation.
• Asymmetric adaptation effects on upward versus downward VOR plateau velocities warrant further investigation.