Role of the vestibular end organs in experimental motion sickness - A primate model

Experimental studies of the role of vestibular end organs in motion sickness experienced by squirrel monkeys are reviewed. The first experiments in motion-sickness-susceptible squirrel monkeys were performed under a free-moving condition with horizontal rotation and vertical oscillation. In the following experiments, the vestibular-visual conflict in the pitch plane was given to the chair-restrained (upright position) squirrel monkeys. Results of this study showed that the existence of otolith afferents, which continually signal the directional change of gravity and linear acceleration vectors, was necessary for the elicitation of emesis by the sensory conflict in pitch.