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.
Fushiki
Hiroaki
H
Department of Otolaryngology, Faculty of Medicine, University of Toyama, 2630 Sugitani, Toyama-shi, Toyama 930-0194, Japan. hfushiki@ms.toyama-mpu.ac.jp
Maruyama
Motoyoshi
M
Watanabe
Yukio
Y
D000222:Adaptation, Physiological / Q000502:physiology; D000818:Animals; D001921:Brain / Q000502:physiology; D002415:Cats; D005133:Eye Movements / Q000502:physiology; D019416:Head Movements / Q000502:physiology*; D007088:Illusions / Q000502:physiology; D009433:Neural Inhibition / Q000502:physiology; D009760:Nystagmus, Physiologic / Q000502:physiology*; D009949:Orientation / Q000502:physiology*; D004856:Postural Balance / Q000502:physiology*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D014717:Vertigo / Q000503:physiopathology; D014722:Vestibule, Labyrinth / Q000502:physiology*