Adaptation to vection-induced symptoms of motion sickness.

The visual-vestibular-proprioceptive sensory mismatch of vection provokes motion sickness in approximately 60% of healthy subjects. Approximately 60% of astronauts experience motion sickness in microgravity where vestibular/otolith function is altered. The purpose of this study was to determine the extent to which symptoms of motion sickness and tachygastria, an abnormal 4-9 cpm rhythm of the stomach, decrease or adapt during three repeated exposures to a rotating circular vection drum. Subjects sat in the drum for 45 min: 15 min baseline, 15 min drum rotation at 60 degrees.s-1, and 15 min recovery. Gastric myoelectric activity was continuously recorded with the electrogastrogram (EGG). Symptom reports were obtained during rotation. In Experiment I, 10 subjects were exposed to the drum 3 times with intersession intervals of 4-24 d. They failed to show adaptation based on subjective reports and all showed tachygastria. In Experiment II, 14 new subjects were exposed to the drum 3 times with intersession intervals of 48 h. The group experienced a reduction in symptoms and tachygastria with repeated exposure to the drum. Thus, symptomatic and physiological improvement occurred after training in subjects susceptible to vection-induced motion sickness. Preflight adaptation to visual-vestibular sensory mismatch may reduce motion sickness experienced in the environment of microgravity.