Vestibular evoked myogenic potential threshold and seasickness susceptibility

Numerous attempts have been made to find physiological parameters that might predict susceptibility to seasickness. However, to date, no physiological index has been found that can serve as a diagnostic tool for individual susceptibility to motion sickness at the personnel selection stage. A number of studies have demonstrated that linear acceleration in the vertical plane is the most provocative stimulus of motion sickness. The main physiological sensory modality responsible for monitoring vertical acceleration is the saccule. Over the last decade, vestibular evoked myogenic potentials (VEMP) have come to be recognized as a reliable procedure for the evaluation of saccular function. We used the VEMP test to assess otolith responses in 15 seasickness-susceptible (SS) and 15 non-seasickness-susceptible (NSS) healthy male crew members. The SS group exhibited a significantly higher VEMP threshold and a significantly lower peak-to-peak p13-n23 amplitude interval compared with the NSS group. Further analysis by logistic regression found threshold to be the dominant factor associated with seasickness susceptibility. The study demonstrated differences in the VEMP reflex of the SS and NSS groups. The threshold difference may represent an intrinsic mechanistic difference between the vestibular systems of the two groups. Theoretically, increased susceptibility to seasickness may be due to a discrepancy between the various neural systems as a result of reduced otolith responses.