European vestibular experiments on the Spacelab-1 mission: 7. Ocular counterrolling measurements pre- and post-flight

Abstract

The static ocular counterrolling (OCR) of the four scientific crew members in the first Spacelab mission was measured during baseline-data-collection before and after the flight of SL-1. It was presumed that the modification of otolithic responses during spaceflight will be reflected in specific changes of the OCR-gain on the first days after recovery. The magnitude of OCR was determined analysing colour-transparencies of subjects right eyes that were produced in different positions of lateral body tilt. In general, one subject did not show any changes at all; three subjects exhibited a significant decrease of OCR-gain after exposure to weightlessness, whereby differences could be found between the responses for small and large angles of lateral body tilt. Moreover, asymmetrical effects of OCR-gain were found between body tilt to the left and tilt to the right side. Two subjects already demonstrated such an asymmetry before the flight with the higher gain on left-tilt (or right eye up), and three subjects exhibited left-right asymmetries after the spaceflight with the higher gain tilting to the right (or right eye down). A possible correlation between these vestibular asymmetries and space-sickness susceptibility is discussed.

The Vestibular System: A Newly Identified Regulator of Bone Homeostasis Acting Through the Sympathetic Nervous System

“…Similar to aged subjects, remodeling of synaptic connections in vestibular sensorial hair cells and an increase in the number and the size of synaptic knobs have been reported in adult rats during shortterm space missions [111,112]. The vestibulo-spinal and vestibulo-ocular reflexes are also altered in these conditions [113][114][115].…”

Binocular misalignments elicited by altered gravity provide evidence for nonlinear central compensation

“…Hence this work would benefit from future parabolic flight experiments that test, for example, in Lunar and Martian g-levels. Thirdly, previous investigators have found an interesting relationship between the magnitude of ocular misalignments in novel g-levels and motion sickness (both parabolic flight motion sickness and SMS) (Kornilova et al, 1983 ; Vogel and Kass, 1986 ; Lackner et al, 1987 ; Diamond et al, 1990 ; Diamond and Markham, 1991 , 1992b ). Since none of our non-astronaut subjects experienced adverse symptoms inflight, we could not compare their ocular misalignments to motion sickness susceptibility.…”

“…We investigated this further by looking for similar trends from previous investigators, but did not find anything conclusive. For example, Vogel and Kass' four crewmembers all showed higher OCR gains during leftward tilts preflight and during rightward tilts post-flight (Vogel and Kass, 1986 ). Diamond and colleagues, however, found the opposite result in seven non-astronaut subjects: larger OCR was observed during rightward tilts than leftward tilts, and the depressed eye torted more than the elevated eye (Diamond et al, 1979 ).…”

“…For instance, Kornilova and colleagues reported a strong correlation between SMS and post-flight ocular counterroll (OCR) asymmetry in Russian cosmonauts (Kornilova et al, 1983 ): eleven out of twelve long-duration crewmembers (missions between 30 and 211 days) who experienced SMS inflight also exhibited asymmetries in OCR post-flight. Vogel and Kass measured OCR elicited by leftward and rightward roll tilts up to 90° in four Spacelab-1 crewmembers pre- and post-mission (Vogel and Kass, 1986 ); the astronaut most prone to SMS expressed the largest asymmetry in OCR gain preflight, while the astronaut least susceptible showed symmetrical OCR gain preflight and quickly returned to baseline levels post-flight. Diamond and Markham performed a series of experiments on astronauts in which they correlated asymmetries in binocular torsion during the altered g-levels of parabolic flight with SMS experience (Diamond et al, 1990 ; Diamond and Markham, 1991 , 1992b ); astronauts who exhibited the largest differences in torsional asymmetry between the 0 and 1.8 g phases of parabolic flight were the ones who endured the most severe SMS during their missions.…”

“…Furthermore, our device fully eliminates binocular visual cues, which are known to mask ocular positioning misalignments (Burian, 1939 ; Ogle and Prangen, 1953 ; Kertesz and Jones, 1970 ; Crone and Everhard-Hard, 1975 ; Kertesz, 1981 ; Guyton, 1988 ; Paterson et al, 2009 ). Previous investigators have captured ocular positions during altered g-level exposure using film cameras in ambient light (Vogel and Kass, 1986 ; Diamond et al, 1990 ; Diamond and Markham, 1991 , 1992b ), and hence the binocular visual cues available to the subjects during testing may have interfered with their ocular misalignment results. We hypothesized that the ocular misalignments quantified through our perceptual nulling tasks would exhibit similar g-level dependencies observed by previous investigators, but may be more accurate and consistent due to the absence of binocular visual cues.…”