Oculomotor reflexes after semicircular canal plugging in cats.

The horizontal ocular reflexes of cats were studied before and after plugging all 6 semicircular canals (2 cats) or the horizontal canals only (2 cats). After plugging, the vestibulo-ocular reflex (VOR) was virtually absent in the cats with all canals plugged; a small phase-advanced VOR was detectable only at high velocities of rotation. There was no VOR recovery over several months. A compensatory cervico-ocular reflex (COR) appeared within a few days of plugging in all cats, and increased in gain slowly over time. The cats with horizontal canals plugged had little VOR during yaw rotation with the head pitched near 30 degrees down from the stereotaxic plane. When the head was pitched nose up from this null plane, a horizontal VOR appeared and increased as the sine of pitch angle, indicating that the cats relied on normal or increased coupling of vertical canals to horizontal eye movers for generation of compensatory eye movements. Periods of compensatory and anticompensatory eye movements were recorded during downward pitched yaw.