Motion sickness and vestibular hypersensitivity

Objective: Motion sickness is poorly understood, although it has been recognized for years as debilitating. Vestibular function is required for motion sickness to occur, but motion sickness can also be brought on without body motion. The aim of this study was to see if there was a correlation between caloric response and motion sickness susceptibility. Design: One experiment was a prospective study carried out on 200 patients. A second prospective study was carried out on 121 patients. Setting: Patients referred to our tertiary/quaternary care dizziness clinic. Methods: In experiment 1, caloric scores in patients were correlated with symptoms of motion sickness as established by responses to a simple question. In experiment 2, caloric scores were correlated with symptomatic responses to caloric testing itself. Main Outcome Measures: Caloric responses of the best ear were measured according to standardized caloric evaluation methods. Results: There was no correlation between motion sickness and caloric scores. There was a significant difference in caloric scores between patients made symptomatic by calorics and those who were not. Conclusions: The autonomic response seen in some patients is not triggered by a specific level of semicircular c anal response (as measured by caloric testing). We hypothesize that (similar to space motion sickness) the trigger is a signal differential that arises between semicircular canals and otoliths and that some patients are unable to suppress this response. These patients often suffer motion sickness on a long-term basis.