Motion sickness susceptibility: a possible source of normal vestibulo-ocular reflex (VOR) variability: The Israel society for EEG and clinical neurophysiology, annual meeting: Jerusalem, 12 November 1991

Seasickness, a common form of motion sickness, is a normal physiological reaction to certain unnatural kinds of motion. A normally functioning vestibular system is a prerequisite for the development of motion sickness. Evaluation of the VOR by the sinusoidal harmonic acceleration (SHA) test is a modern method employed for evaluating the function of the vestibular system. The purpose of this study was to examine whether differences exist in the VOR of persons susceptible and non-susceptible to seasickness. The study was conducted on 69 healthy subjects, 18-23 years old, with normal neuro-otological examination. They were selected according to their susceptibility to seasickness and divided into two groups: non-susceptible (N = 30) and susceptible (N = 39). Subjects were exposed to a series of yaw axis angular SHA at 0.01, 0.02, 0.04, 0.08 and 0.16 Hz in a computerized rotatory chair. The electronystagmographic records for each frequency were analyzed using computerized digital techniques to obtain VOR gain, phase and asymmetry. VOR parameters were within the normal range in both groups, but the susceptible group demonstrated statistically significant higher gain at 0.02, 0.04 and 0.08 Hz and statistically significant lower phase at 0.01, 0.02, 0.04 and 0.08 Hz, in comparison with the VOR parameters of the non-susceptible group. We conclude that normal physiological variability in VOR parameters could be at least partially explained by individual differences in susceptibility to motion sickness. The present results could also be of value in the prediction of motion sickness susceptibility.