Exposure to extended periods of weightlessness in orbital flight has profound effects on the neurovestibular system and influences head and eye movements, postural control, and spatial orientation. The associated space motion sickness is among the earliest of the signs of adaptation to this new environment. This report both reviews the prominent neurovestibular phenomena associated with going into space and returning to earth and relates the issues to vestibular compensation and rehabilitation. New results from the Spacelab SLS-2 mission are included, showing significant reductions in postflight ocular counterrolling and changes in ocular counterrolling left/right asymmetries after 2 weeks in space. (Otolaryngol Head Neck Surg 1998;118:S31-S34.)
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