Motion sickness susceptibility modulates the impact of electrical vestibular stimulation on postural control.

Motion sickness is defined as a sensation of uneasiness that occurs during physical motion, such as transportation by bus, plane, car or train. Postural control is one of the multisensory processes that has been examined in individuals susceptible to motion sickness. Indeed, postural control relies on visual, somatosensory and vestibular information. While studies suggest normal-like postural control during quiet standing, others suggest that individuals with motion sickness show increased postural instability during sensory perturbations, namely during visual and somatosensory disturbances. The impact of vestibular stimulation on postural control in individuals with motion sickness has yet to be determined. Therefore, the aim of the present exploratory study was to examine the effects of sinusoidal electrical vestibular stimulation on postural control in individuals with varying degrees of motion sickness. Fifty participants were divided into three groups based their susceptibility to motion sickness. Participants were initially tested at baseline in the four postural conditions of the modified Clinical Test of Sensory Integration and Balance protocol (mCTSIB): eyes open on firm surface, eyes closed on firm surface, eyes open on foam surface, eyes closed on foam surface. These four conditions were then repeated during sinusoidal electrical vestibular stimulation (EVS) of 1 mA at 1 Hz. In baseline conditions, no significant group differences in postural control were found. Data in experimental (EVS) conditions, however, suggests that individuals with high susceptibility to motion sickness are more impacted by vestibular stimulation, specifically in the eyes closed on firm surface condition. It has been suggested that motion sickness could be the result of an altered multisensory integration process. While the present data do not allow us to answer this question, it would remain important to examine all types of sensory perturbations and combinations thereof in a larger group of individuals.