Gain and phase of cat vertical eye movements generated by sinusoidal pitch rotations with and without head tilt

Vertical EOGs were recorded in cats during sinusoidal head pitch from 0.01 to 4.0 Hz with peak velocities of 50 degrees X s-1. The purpose of the experiments was to determine whether dynamic response properties of the vertical vestibulo-ocular reflex (VOR) elicited by pitch with the animal lying on its side (on-side pitch) differ from those resulting from normal (upright) pitch. During on-side pitch (not changing head position with respect to gravity), the vertical VOR gain was 13.5% less than during upright pitch. Thus, the vertical VOR was more compensatory than during on-side pitch. Phase did not differ between the two conditions. The results indicate the importance of interactions between otolith and vertical canal stimulation for vertical eye movement control. The results imply that in micro-gravity, where head tilt does not lead to otolith stimulation as regards gravity, vertical head and eye movements may not be controlled appropriately, leading to vestibular-visual conflicts at the same time that horizontal eye movement controls are normal.