Subjects: Eight International Space Station (ISS) crewmembers were recruited to participate in three preflight sessions (between 120 and 60 days before launch) and then three postflight sessions on R+1 day (+24 hrs following direct return to Johnson Space Center-JSC), R+4 (± 2) days, and R+8 (± 2) days. An informed consent briefing has been delivered to 26 ISS crewmembers between March 2014 and May 2018. The last crewmember was recruited on May 2018 after which the enrollment was closed. Preflight data was initiated in 2015 following approval for this study to be implemented for pre- and post-flight testing only. One subject was withdrawn from the study due to changes in post-flight test plans. Eight ISS crewmember (5 male, 3 female; mean age 49.6 ± 9.3 years) have completed pre- and post-flight data collection. The mean duration of their spaceflight was 188 ± 79 days.219
Specific Aim 1
The amplitude of perceived tilt during passive tilt in roll (± 25º) significantly increased on R+1 compared to preflight. However, the amplitude of perceived tilt during passive tilt in pitch (± 15º) did not change significantly on R+1 compared to preflight. The perceived amplitude of translation tended to increase during roll tilt and during pitch tilt after spaceflight. The perception of distances of visual targets ranging from 0.5 m to ~2 m was affected by target distance, with greater errors with near targets =1 m. However, the distance of a visual target was not affected by spaceflight within the timeframe of our tests. The eye movement data indicate that the amplitude of ocular counter-rolling during tilt in roll was reduced for several days after return from long-duration spaceflight. This decrease in amplitude was not accompanied by changes in the asymmetry of OCR between right and left head tilt (Reschke et al. 2018).
Specific Aim 2
When subjects imagined a laboratory-fixed target while being tilted in pitch at angles varying from 15º backward to 15º forward, the vertical eye position shifted downward ~5º compared to when they were actually looking at the target, thus indicating a downward shift of the subjective straight-ahead. The addition of a vibrotactile feedback of tilt when the subjects imagined the targets partially compensated for this downward shift of the subjective straight-ahead. This result confirms that a vibrotactile feedback is a useful countermeasure after landing for mitigating the effects of spaceflight on spatial disorientation and manual control (Clément et al. 2018; Reschke & Clément 2018).
Specific Aim 3
The translational vestibulo-ocular reflex (tVOR) measurements during vertical oscillations were analyzed using a method that has been recently published (Clément et al. 2019). The tVOR at high frequency is an important otolith-mediated response to stabilize gaze during natural locomotion. The tVOR was significantly increased with near viewing of actual targets. This effect was less pronounced with subjects imagining these targets in darkness. A decrease in the tVOR gain was observed in some subjects, which could potentially alter gaze fixation during locomotion. Therefore, the results of this study confirm the potential contribution of a spaceflight-adapted vestibular system in locomotion impairment after spaceflight.
The results of this study indicate that after spaceflight, there is an over-estimation of perceived roll tilt, but that there is no change in perceived pitch tilt. Also, the perceived amplitude of translation tends to increase during roll and pitch tilt after spaceflight.
Ocular counter-rolling during roll tilt decreases after long-duration spaceflight.
The subjective straight-ahead shifts downward after spaceflight (~ 5º). A vibrotactile feedback of tilt partially compensates for this downward shift in some subjects.
One primary limitation of this study is the delayed testing due to the time required for direct return to JSC. Recent field tests (Reschke et al. 2020) suggest that any impairments observed following +24 hrs underestimate the initial decrement soon after landing.
The observed changes in egocentric reference might impair an individual’s ability to evaluate the direction of an approaching object or the accuracy of their reaching movements or locomotion. The use of vibrotactile sensory aid partially compensates to correct the representation of the body tilted relative to gravity and could partially help in mitigating risks caused by this loss of spatial orientation.
Reschke MF, Wood SJ, Clément G (2018) Ocular counter rolling in astronauts after short-and long-duration spaceflight. Scientific Reports 8: 7747.
Clément G, Wood SJ, Paloski WE, Reschke MF (2019) Changes in gain of horizontal vestibulo-ocular reflex during spaceflight: Journal of Vestibular Research 29: 241-251.
Clément G, Reschke MF, Wood SJ (2018) Vibrotactile feedback improves manual control of tilt after spaceflight. Frontiers in Physiology 9: 1850.
Reschke MF, Clément G (2018) Vestibular and sensorimotor dysfunction during spaceflight. Current Pathobiology Reports6 (3): 177-183.
Reschke MF, Kozlovskaya IB, Lysova N, Kitov V, Rukavishnikov I, Kofman IS, Tomilovskaya ES, Rosenberg MJ, Osetsky N, Fomina E, Grishin A, Wood SJ. (2020) [Joint Russian-USA field test: Implications for deconditioned crew following long duration spaceflight]. Aviakosm Ekolog Med. 2020;54(6):94-100.