Space motion sickness and spatial orientation of vestibulo-ocular reflex

Abstract

Space motion sickness is a condition which frequently occurs shortly after attainment of sustained exposure to microgravity and affects 73% of crew members on the first 2 or 3 days of their initial flight. The characteristic symptoms and signs include vomiting, retching, pallor, flash, cold sweating, yawning, belching, flatulence, and decreased gastric tonus. The severity of space motion sickness is variable, but over half of the cases are categorized as moderate to severe. In-flight and post landing immunity to the coriolis sickness susceptibility test (CSSI) observed during the Skylab M131 experiment suggests that the otolith organs play an important role in space motion sickness. This view is supported by a study that ocular counter rolling asymmetries are correlated with space motion sickness incidence and severity. It has also been reported that sensory-motor adaptation to microgravity includes a process whereby central interpretation of the otolith signal is biased from tilt toward translation. Perceptual studies provide some support for this 'otolith tilt-translation reinterpretation' hypothesis and have also suggested orientation to the long axis of the body or to the surrounding spacecraft after adaptation to microgravity. In the Neurolab project, using space shuttle 'Columbia', several experiments were performed to determine how microgravity affects the orientation vectors of the vestibulo-ocular reflex (VOR) and optokinetic nystagmus (OKN) and how they are altered by introducing a linear force due to centrifugal acceleration in an eccentric rotator. We discussed here, some current aspects regarding space motion sickness.