Efficacy of tilt-suppression in postrotatory nystagmus in cats

The phenomenon of tilting the head away from an upright position immediately after a horizontal head-rotation, thus reducing the duration of postrotatory nystagmus (PRN), has more than once been called "tilt-suppression." It represents an example of the semicircular canal-otolith interaction in the central vestibular system. In the present study we investigated how head roll-tilt influences the time constants of PRN in the horizontal and vertical planes in cats. The head/body was roll-tilted by 30 degrees toward the upright or the side down from initial roll positions immediately after termination of earth-vertical axis (EVA) rotation. Changes in head orientation either towards or away from the EVA reduced horizontal PRN. The reducing effect was small when the head was roll-tilted toward the EVA. Vertical nystagmus decreased only when the head orientation moved toward alignment with the EVA. Otolithic "tilt-suppression" may be a central neuronal mechanism that is activated to minimize the tumbling sensation of turning about a tilted axis and postural instability, but our results indicate that tilt-suppression of PRN depends on a change in head orientation with respect to the EVA.