Effects of Spaceflight on the Vestibular System

Abstract

Here on Earth, the vestibular system provides sensory information to assist with orientation and motion perception, balance, locomotion, stabilizing eye movements, and various other functions. In orbital spaceflight, the microgravity environment results in altered vestibular cues, particularly to the otolith organs. Fortunately, the central nervous system is able to reinterpret the altered vestibular cues and adapt to the microgravity environment within a few days. However, these microgravity-induced vestibular adaptations are inappropriate upon return to Earth or another gravity-rich environment (e.g., the Moon or Mars). Various conceptual hypotheses have been proposed for the vestibular reinterpretation in microgravity. These hypotheses make specific predictions for how orientation and motion perception are altered immediately upon landing while still adapted to microgravity. This chapter reviews the evidence from previous studies that have investigated orientation and motion perception in astronauts post-flight. The data is limited by operational concerns but suggests that tilt perception may be partially misinterpreted as translation, particularly for higher-frequency (i.e., faster) tilts, though a sense of tilt remains. In addition, tilt is often overestimated, particularly at lower frequencies (i.e., slower or static tilts), while translation is overestimated at higher frequencies. These findings are assessed in light of previous conceptual hypotheses for vestibular reinterpretation to microgravity. The operational impacts of astronauts’ impaired sensorimotor function are reviewed. Proposed neurovestibular countermeasures are summarized, particularly in the context of future crewed Mars exploration.