Computerized dynamic posturography and seasickness susceptibility

Objective/Hypothesis: The neural mismatch theory emphasizes the role of con flicting multimodal sensory interactions in producing both motion sickness and the rearrangement process that finally leads to habituation to the adve rse motion conditions, If this theory is, indeed, correct, the patterns of the response to the integrated signal from simultaneous multisensory stimul ation, characterized by unusual relationships between the senses responsibl e for spatial orientation, should differ according to motion sickness susce ptibility, Computerized dynamic posturography (CDP) provides the opportunit y to simultaneously change the interactions between visual, somatosensory, and vestibular inputs, thus giving an indication of the relative importance of these senses in maintaining balance, The objective was to investigate b alance strategies in naval crew members with differing susceptibility to se a conditions using CDP, Study Design: Cross-sectional, parallel-group desig n. Methods: Twenty subjects susceptible to seasickness (SS) and 20 nonsusce ptible subjects (NSS), healthy male volunteers aged 18 to 25, were tested u sing the EquiTest system (NeuroCom, Inc., Clackamas, OR). Results: The SS g roup exhibited significantly less stability than the NSS group in condition 5 of the sensory organization test (SOT). The ratio of the SOT scores of c onditions 5 to 1 (the vestibular organization pattern) was also found to be significantly lower in the SS group. Conclusions: The results suggest that SS might be more dependent on somatosensory and visual inputs and less on vestibular inputs for maintenance of balance compared with NSS, Higher susc eptibility to seasickness might reflect abnormal weighting of sensory modal ities during the integration process, This would result in disruption of th e integration process required to maintain balance and a sense of orientati on in space in conditions producing conflicting sensory inputs.