Role of otolith endorgans in the genesis of vestibular-visual conflict sickness (pitch) in the squirrel monkey (first report).

This experiment was designed to clarify each vestibular submodality's role in the genesis of vestibular-visual conflict sickness in pitch. We wanted to determine whether the ablation of the macula utriculi and macula sacculi, totally or separately, unilaterally and bilaterally, preserving the semicircular canals intact, could eliminate the conflict emesis in the squirrel monkey model. Observations were carried out over 5 months. In susceptible animals, the difference in conflict sickness scores between the pre- and the postutriculosacculectomy conditions was statistically significant. However, in less susceptible animals, the scores were low from the beginning and the differences were not statistically significant. Unilateral sacculectomy was performed at the smallest otolith endorgan lesion. The conflict sickness scores declined significantly and no emesis occurred. However, at 4.5 months after the operation, animals regained their preoperative scores; thus indicating that the afferents from the remaining endorgans were sufficient to provoke the sickness. This result indicated that functional neural adaptation took place within the equilibrium system. The trial repetition in normal animals and stapedectomized controls did not produce any clear score change.