Unusual vestibular and visual input in human dynamic balance as a motion sickness susceptibility test.

BACKGROUND: Motion sickness (MS) is commonly thought to arise from a sensory conflict. However, few quantitative methods based on this theory are available to detect MS susceptibility. HYPOTHESIS: It was asked whether the standardized unusual stimulation of a single sensory channel under quantified dynamic balance conditions in man could elicit a sensory conflict and therefore trigger motion sickness (MS) METHODS: Vestibular and visual channels were stimulated by galvanic current and rotating prismatic glasses, respectively. The moving platform used to create the requirements for dynamic balance conditions was chosen not only to worsen the malaise but also to obtain an objective measurement of the balance consequences of the stimulations. RESULTS: Both vestibular and visual stimulation, applied separately, elicited MS-like symptoms (in 56% and 73% of subjects, respectively) and stereotyped balance reactions. A relationship was found between subjective MS-like symptoms and objective measurements of dynamic balance performance. Subjects sensitive to unusual vestibular messages differed from the others by a greater increase in the parameters indicating a difficulty of balance whereas subjects sensitive to unusual visual messages were recognized by the strategy they used to balance themselves. CONCLUSIONS: These results demonstrated that a sensory conflict can trigger MS-like symptoms. We conclude that the measured parameters of a global somatomotor activity, such as the dynamic balance task proposed here, could be useful for objectively detecting subjects predisposed to MS, for training them and testing the efficiency of anti-MS drugs.