Higher Asymmetry Ratio and Refixation Saccades in Individuals with Motion Sickness.

BACKGROUND

Motion sickness is a complex autonomic phenomenon caused by the intersensory conflict among the balancing systems, resulting in a mismatch of signals between static physical conditions of the susceptible individual exposed to dynamic environment.

PURPOSE

The present study was done to assess the sacculocollic reflex pathway and six semicircular canals in individuals susceptible to motion sickness.

RESEARCH DESIGN

Standard group comparison was used.

STUDY SAMPLE

A total of 60 participants with an age range of 17-25 yr were included, where group I comprised 30 participants with motion sickness and group II comprised 30 participants without motion sickness. The Motion Sickness Susceptibility Questionnaire-Short was administered to classify the participants into groups with or without motion sickness.

DATA COLLECTION AND ANALYSIS

The cervical vestibular-evoked myogenic potential (cVEMP) test and video head impulse test (vHIT) were administered to all participants. The Shapiro-Wilk test revealed normal distribution of the data (p > 0.05). Hence a parametric independent sample t test was done to check significant difference in cVEMP and vHIT parameters between the two groups.

RESULTS

The present study revealed no significant difference for cVEMP latencies and amplitude in individuals with motion sickness. However, significantly higher cVEMP asymmetry ratio was observed in individuals with motion sickness. Though the vestibulo-ocular reflex (VOR) gain values showed no significant difference between the two groups except for the right anterior left posterior plane, the asymmetry in VOR gain values revealed significant difference between the groups, suggesting asymmetry as a better parameter than absolute VOR gain values. Also, the presence of refixation saccades in 100% of the individuals with motion sickness accorded with various studies reported earlier with vestibular-related pathologies.

CONCLUSIONS

Presence of higher asymmetry ratio in cVEMP and vHIT test results plus refixation saccades to stabilize the gaze in vHIT can suggest some amount of vestibular anomalies in individuals with motion sickness.