Exploring Vestibulo-Masseteric Pathways: An Insight into Motion Sickness Susceptibility.

Background: Motion sickness is an autonomic reaction to sensory conflict among vestibular, somatosensory, and visual inputs, manifesting as drowsiness, dizziness, discomfort, nausea, pallor, sweating, headache, malaise, vomiting, and apathy. Although vestibular function in motion sickness has been probed using various vestibular tests, the utility of masseter vestibular evoked myogenic potential (mVEMP)-a novel assay of the vestibulo-masseteric reflex elicited via masseter muscle stimulation-remains largely unexplored. Purpose: This study sought to explore mVEMP responses among individuals with different degrees of motion sickness susceptibility (MSS) and to determine the relationship between individual susceptibility levels and their corresponding peak-to-peak mVEMP amplitudes. Research Design: Cross-sectional study design. Study Sample: A total of 45 young adults (18-35 years old) were enrolled and stratified into three susceptibility cohorts-nonsusceptible (n = 15), mild-to-moderate (n = 15), and severe (n = 15)-based on their Motion Sickness Susceptibility Questionnaire-Short scores. Data Collection and Analysis: Ipsilateral mVEMP responses were evoked using a 500-hertz narrow-band CE-chirp delivered through a zygomatic electrode montage, and the resulting waveforms were analyzed for P11 and N21 peak latencies, P11-N21 peak-to-peak amplitudes, and interaural amplitude asymmetry ratios. Results: Inferential analysis revealed no significant differences in P11 and N21 latencies across the nonsusceptible, mild-to-moderate, and severe MSS groups, as seen in both individual and group-level data. In contrast, P11-N21 peak-to-peak amplitudes showed group-wise variation in both analyses. A Kruskal-Wallis H test revealed significant amplitude differences bilaterally across the three cohorts. Subsequent post hoc comparisons demonstrated that participants with severe MSS exhibited significantly reduced mVEMP amplitudes compared with the nonsusceptible group. Conclusions: Severe motion sickness may reflect underlying vestibular alterations, possibly involving the vestibulo-masseteric pathway. Therefore, although mVEMP may hold potential clinical utility in diagnosis, this should be interpreted with caution. Clinical Relevance Statement: mVEMP may serve as a useful objective measure for assessing vestibular integrity in individuals susceptible to motion sickness, with reduced peak-to-peak amplitude potentially indicating subtle physiological changes in the vestibular system. However, these results should be interpreted with caution because of variability in individual responses, and they underscore the need for further studies to validate the findings.