Bilateral Asymmetry in Ocular Counter-Rolling Reflex Is Associated With Individual Motion Sickness Susceptibility

Abstract

Accumulating evidence suggests that individual variations in vestibular functions are associated with motion sickness (MS) susceptibility. We investigated whether vestibular functions in the reflex and cortical pathways could predict the susceptibility of individuals to MS. MS-susceptible and control adults were recruited according to the Motion Sickness Susceptibility Questionnaire (MSSQ) score. Otolith reflex and cortical functions were assessed using the ocular counter rolling test and the head-tilt subjective visual vertical (HT-SVV) test, respectively. The bilateral asymmetry of each function was compared between the MS-susceptible and the control groups. Although the two tests for otolith functions were conducted using the same stimulation (lateral head tilt), bilateral asymmetry of otolith reflex rather than cortical function was significantly associated with MS susceptibility. Our data suggests that bilateral asymmetry in the otolith reflex pathway is capable of predicting susceptibility to MS to some extent. Our data also suggest that the association between vestibular function and MS susceptibility can vary based on the vehicle types. Future vehicles, such as self-driving cars, will make us aware of other vestibular functions associated with MS susceptibility.

Keywords: cortical pathway; motion sickness susceptibility; ocular counter-rolling; reflex pathway; subjective visual vertical; vestibular function.

Figure 1

Flowchart of the screening process. N, F, and M denote numbers of group, female and male participants, respectively. Age and MSSQ denote means ± SEM of age and Motion Sickness Susceptibility Questionnaire (MSSQ) score, respectively.

Figure 2

(Caption of Y is revised) Distribution of MSSQ scores in the qualified applicants. Colored parts of both ends depict MSS (red, < 25th percentile) and control (blue, > 75th percentile) participants, respectively.

Figure 3

Records of subjective visual vertical (SVV) and ocular counter-rolling (OCR) tests from a MS susceptible individual. (A) Slope of lines depict left (based on rectangle-dots) and right (based on triangle-dots) head-tilt subjective visual vertical (HT-SVV) gain (S_l and S_r, respectively). Circle dots are used to calculate head-upright SVV. (B) Eye torsion (blue thin line) and head tilt (gray bold line) angle during the OCR test. Short horizontal bars depict 5 s time periods used for calculating OCR gains.

Figure 4

Correlations between functional asymmetry in HT-SVV (I_SVV) and in OCR (I_OCR) tests from 51 participants.

Figure 5

Comparison in IOCR (A) and Isvv (B) asymmetry indices, respectively, between MS susceptible (MSS) and control groups. *indicates a significant difference.

Figure 6

Mean MSSQ sub-scores by vehicle types from the control group (triangle) and MSS subgroups with high (circle) and low (rectangle) OCR asymmetry. Error bars denote SEM. *indicate significant differences between MSS subgroups.