Compensatory function of the Vertical Vestibulo-Ocular Reflex (VVOR) in the alert rabbit - the brain in health and desease

The EMG activity of the vertical eye muscles of alert rabbits submitted in the dark to sinusoidal rolls (±5°; 0.O1-O.5Hz) has shown an increase of the phase lead of the response by increasing the stimulus frequency. In the same alert preparation, vertical eye movements evoked by the same pattern of vestibular stimulation were recorded by means of an infrared light device. At all the tested frequencies the recorded eye position was about 180° out of phase with respect to head position. This indicates that, contrary to the horizontal one, the VVOR is compensatory ven for very slow head displacement. The comparison between the phase of the EMG responses and that of the eye movements points to the important contribution of the eye ball mechanical properties which introduce a phase lag in the response INCREASING FROM 0-10° AT 0-01 Hz to 40-50° at 0.5 Hz.