Mechanisms of Motion Sickness as Reflected in the Vertigo and Nystagmus Responses to Repeated Caloric Stimuli

Abstract

In the routine caloric test a group of seamen, who stated that they practically never had been motion sick, had vertigo and nystagmus responses of lower average intensity than those of a group of seamen who asserted that they were somewhat troubled by a tendency to become motion sick. Those subjects who had distinct vertigo responses and “normal” nystagmus responses at the routine test were selected for a study of the responses to repeated identical monolabyrinthine caloric stimulations. In both groups there was habituation in the vertigo and in the nystagmus responses, and the habituation curves were approximately parallel. The vestibular mechanisms which are known to be of importance in the development and persistence of motion sickness are discussed. It is concluded that the group difference observed in the routine caloric test is probably due to a difference in the sensitivity of the labyrinthine sense-organs.