The otolithic contribution to vertical ocular stability in the cat

Area of Science:

• Neuroscience
• Ophthalmology
• Vestibular System Research

Background:

• The vestibulo-ocular reflex (VOR) stabilizes gaze during head movements.
• Understanding vertical VOR (VVOR) and its interaction with other reflexes is crucial for gaze control.
• Previous studies have not fully elucidated the role of otolithic input, like the maculo-ocular reflex (MOR), in VVOR under varying conditions.

Purpose of the Study:

• To investigate the characteristics of horizontal (HVOR) and vertical (VVOR) vestibulo-ocular reflexes in cats.
• To examine the combined effects of vestibular and optokinetic stimulation on ocular responses.
• To determine the influence of gravity modulation on VVOR and the contribution of the maculo-ocular reflex (MOR).

Main Methods:

• Cats were subjected to horizontal and vertical sinusoidal rotations at various frequencies.
• Vestibular stimulation was combined with optokinetic stimulation.
• VVOR was tested in upright (0 degrees) and side-down (90 degrees) positions; semicircular canals were plugged to isolate the MOR.

Main Results:

• Upright VVOR showed higher gain and less phase lead than HVOR below 0.05 Hz.
• Optokinetic stimulation increased horizontal and vertical VOR gain towards 1.
• Side-down VVOR exhibited asymmetric responses, with downward movements showing lower gain and greater phase lag; MOR contributed significantly to upright VVOR gain, acting as a low-pass filter.

Conclusions:

• Otolithic coactivation via MOR enhances VVOR gain and reduces phase lag, improving gaze stability across vertical and horizontal planes.
• Combined vestibular and optokinetic stimulation normalizes upward and downward ocular responses.
• The maculo-ocular reflex modulates the amplitude and frequency of vertical quick phases during vestibular stimulation.