Accordingly, the goal of this project was to develop a portable hand-held device that will allow a single crewmember to assess his/her sensorimotor function in no more than 20 minutes. Investigators developed the Sensorimotor Assessment and Rehabilitation Apparatus (SARA) It’s small, requires little power and space, and provides what is essentially a self-contained sensorimotor lab/clinic.
Development of a device and software for sensorimotor assessment and rehabilitation was the ultimate goal of the project. It assessed performance on sensorimotor tasks determined to be most relevant based on the simulated space flight task, previous parabolic-flight experience, and knowledge of adaptation to long-duration space flight. The device and procedures provided a simple and rapid process for measuring these sensorimotor tasks, without assistance and in minimal time (15-20 minutes). Testing of the device and procedures were with sensorimotor analogs and parabolic flight. Testing in parabolic flight was a key component, as it produces some effects similar to those of space flight, albeit acutely, including alterations in otolith-ocular function, posture, locomotion, and motor control.
Normal healthy subjects wore 0.5X minifying lenses for 20 minutes, during which they performed pitch-plane gaze-stability exercises to adapt their VOR gain. During adaptation, subjects were exposed to one of two postural stances: (1) SIT – seated on an upright chair with feet flat on the floor, or (2) STAND – standing on three-inch-thick foam with heels and toes together and arms crossed. VOR adaptation was assessed through simultaneous eye and head movement recordings, as subjects made active pitch and yaw head rotations while imagining a distant visual target in the dark. VOR gain was defined as the ratio of peak-to-peak eye position to peak-to-peak head position. During adaptation, VOR gain was measured every five minutes in four conditions: (1) pitch plane SIT, (2) yaw plane SIT, (3) pitch plane STAND, and (4) yaw plane STAND.
All subjects adapted to the minifying lenses, as verified by reduced VOR gain following adaptation. In the pitch-plane tests, subjects displayed the largest amount of adaptation when tested in the condition most similar to that used during adaptation: those who adapted in SIT showed the most adaptation during SIT tests, and those who adapted in STAND showed the most adaptation during STAND tests. This represents a type of contextual adaptation. On the other hand, there was a small amount of transfer of adaptation from the pitch plane to the yaw plane in most subjects, indicating generalization.
Variability in VOR gain was larger during pitch than yaw, perhaps because the sensorimotor system is accustomed to compensating for pitching head movements during locomotion and so allows for some amount of normal deviation in that direction. Results suggest that the rate of VOR adaptation is faster during STAND verses SIT adaptation; this may be because the central nervous system as a whole must compensate for the more challenging balance condition quickly to minimize fall risk.
Parabolic flight testing
VON: The subject’s task was simple and easily accomplished, although screen glare was a distraction. The nulling task overall was not as intuitive as investigators would’ve liked: the subject must ignore the frame of the tablet computer in judging target motion. Investigators again verified that pitch VOR gain is higher in the high-g phase of flight, although scatter is large.
Skew: The subject’s task was rapid, easy, and intuitive. Torsional measures showed a small disconjugacy. Vertical skew measures were initially inconsistent and showed no systematic effects, but this has been improved.
Posture: Motion sensors provided data of sufficient quality for postural assessment. Posture was stable in baseline testing: there was very little body motion during head movements. Upon early exposure to lunar g (non-adapted), there was considerable body motion in all three axes during head motion, especially in yaw as the subject attempted to maintain center-of-pressure over the feet in the face of unreliable vestibular information on head/body motion.
Locomotion: Data quality was sufficient to assess locomotion. The wireless link from sensors to the tablet computer did not drop out as the subject moved. Locomotion in lunar g was not dramatically altered and did not change much over four flights, although head yaw was more tightly controlled after several flights. The head and body turned together early in flight; after adaptation to lunar g, head motion led body motion. The latter is more natural, where the head turns first to see where to go, followed by the body turning. The coupled head-body motion seen early resembles that seen in vestibular patients, and again shows that the developed technology can detect even subtle sensorimotor alterations.
Skew assessment and validation
During flights in April 2013, SARA technology was tested in different g levels. During baseline testing on the ground, roll tilts that activate the otolith organs might be expected to produce skew if there was an otolith asymmetry. In an initial set of subjects there were significant differences between the three head orientations, and although the differences were small the variability was well-controlled, enabling reliable statistical determinations. Testing in the three g levels of parabolic flight (0g, 1g, ~2g) also yielded clear differences between conditions.
This study was continued by Sensorimotor Assessment and Rehabilitation in Parabolic Flight (Sensorimotor_Rehab) with Michael Schubert as the PI.
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