Modulation of vestibulo-ocular reflex (VOR) by active stabilization of head to trunk.

Horizontal vestibulo-ocular reflex (VOR) with covered eyes was tested in 15 healthy subjects sitting on a rotation chair (40 degrees, 0.05, 0.1, 0.2, 0.33 Hz) under two conditions: (a) head fixed to chair by a neck support; (b) with instruction to turn the head together with the passively moved trunk. In situation (b), saccadic amplitudes/sec, nystagmus frequency, gain of nystagmus slow phase velocity and amplitudes of maximum eye shift were enhanced significantly. The phase of maximum eye shift changed from 180 degrees up to 270 degrees with respect to stimulus position. The distribution of nystagmus saccades over the stimulus period showed enhanced peak values and a slight phase shift.