Astronauts experience sensorimotor disturbances during the initial exposure to microgravity and during the re-adaptation phase following a return to an earth-gravitational environment. These alterations may disrupt the ability to perform mission critical functional tasks requiring ambulation, manual control and gaze stability. Interestingly, astronauts who return from space flight show significant inter-subject variations in their abilities to readapt to a gravitational environment. The ability to predict the manner and degree to which each individual astronaut will be affected would improve the effectiveness of countermeasure training programs designed to enhance sensorimotor adaptability.
This project will characterize a set of predictive measures that include: 1) behavioral tests to assess sensory bias and adaptability; 2) imaging to determine individual brain morphological features; 3) genotype markers for genetic polymorphisms that play a role in the neural pathways underlying sensorimotor adaptation. These behavioral, brain morphological/functional and genomic measures will be significantly correlated with individual differences in sensorimotor adaptability (SA) after long-duration space flight. Information from this study will help in the design of sensorimotor adaptability training countermeasures that may be customized for each crewmember’s individual characteristics.
Investigators are conducting a retrospective study using data from relevant ongoing/completed space flight studies. They will leverage data collected from the following long-duration space flight studies: Physiological Factors Contributing to Postflight Changes in Functional Performance (Functional Task Test) (FTT); Spaceflight Effects on Neurocognitive Performance: Extent, Longevity, Neural Bases (NeuroMapping); Postural equilibrium control evaluation as a Medical Requirement; and Recovery of Functional Performance Following Long Duration Space Flight (Field_Test). Participants in the space flight study will be invited back to enable investigators to obtain the proposed predictive behavioral and genomic measures.
APPROACH:
This study has been streamlined to make use of existing MRI data sets and to collect data from recruited crewmembers during one session that will be roughly 95 minutes in duration. Investigators will share pre and post space flight retrospective International Space Station (ISS) crewmember data. Investigators will analyze data that may have been acquired pre-flight/bed rest and post- flight/bed rest when subjects participated in previous space flight missions as part of the Functional Task Test, Pilot Field Test or Field Test studies: Seat Egress, Tandem Heel-to-Toe Walk Test, Recovery from Fall/Stand Test, Object Translation Test, and Jump Down Test.
Subjects will perform the following tests of individual sensory bias.
Treadmill Visual Dependency Test: To test their individual visual dependency during five minutes of treadmill walking, subjects will be presented with incongruent visual flow, a computer generated continuously forward moving with sinusoidal lateral motion virtual hallway scene, projected onto a large screen positioned in front of the subjects. Visual dependency will be assessed by measuring the magnitude of torso translation during scene motion using video motion capture techniques. Retro-reflective spherical markers will be positioned bilaterally at T12. Kinematic torso data will be low-pass filtered with a recursive second-order Butterworth filter at a cut-off frequency of 5 Hz. Torso motion will be defined using the midpoint between the two T12 markers and resulting waveform will be analyzed in the frequency domain. The magnitude of visual dependency will be indicated by the amplitude of the torso movement at the scene’s oscillating frequency. Higher amplitudes at the scene’s oscillating frequency will indicate greater visual dependency.
Vestibular Perceptual Threshold Test: In this test, subjects will experience small motions and be asked to report whether they were moved to the left or to the right along with their degree of confidence (0-100%). Subjects will be comfortably seated in a chair mounted on a commercially available six-degree-of-freedom electric motion base. Subjects will sit in a chair upright, and straps and formable padding will help restrain them securely and comfortably in the chair and minimize pressure points. A head restraint system will apply pressure using conformable foam pads to restrict their head movements. Testing will be done in the dark with the subject wearing vision occluding goggles. A total of up to 50 trials will be performed during testing. Approximately eight trials will be provided for training or until the subject feels comfortable with the task. The total testing time will be less than 10 minutes.
Supine Posture Test (Gravity Bed): This test will use protocols similar to those performed in a supine position in an environment providing the perception of an upright position with respect to gravity. Subjects will “stand” in a supine position while strapped to backpack frame holding a friction-free device using air-bearings that allow the subject to move freely in the frontal plane, similar to when in upright standing. Subjects will perform 10 timed trials of one-legged standing in the tilted room with their eyes closed and their arms crossed across the chest with weights equal to 60 percent of body weight attached to the weight stack. Subjects will be instructed to first find their balance on one leg with their eyes open and then close their eyes. Time will be measured until balance is lost.
In addition subjects will complete tests to assess individual strategic and plastic-adaptive capability.
Adaptive Functional Mobility Test (AFMT): The subject will negotiate a complex obstacle course placed on medium density foam while wearing up-down vision displacing goggles. The dependent measure will be the time to complete the course. The investigators used a similar locomotion test in both of their ground-based and space flight studies. Strategic changes will be characterized by the adaptation rate of each subject over 10 trials. A multilevel exponential recovery model will be fitted to the log-transformed time-to-complete data.
Treadmill Sensory Discordance Test: As a comprehensive measure of overall adaptive capability subjects will walk on a treadmill-motion base system while being exposed to incongruent visual flow and support surface movement. Measures of balance control will be obtained to produce an assessment of adaptive performance. Support-surface variation will be produced by a commercially available six-degree-of-freedom electric motion base on which a treadmill is mounted. A computer-generated hallway scene will provide the visual stimulus. Subjects will walk at 4.0 km/h on the treadmill-motion base for a 3-minute baseline walking period with no scene or base motion followed by 5-minutes of walking (4.0 km/h) with support surface motion consisting of sinusoidal roll of the support surface and a visual scene with a doubled forward visual flow rate that is 90 degrees out of phase with the base motion. A series of audible tones, with variable wait periods between tones will be presented during walking. Subjects will respond to the audible tones by pressing a thumb-switch. To measure stride frequency, footswitches will be affixed to shoe soles at the heels and will be used to define heel-strike events. The mean stride frequency, during each minute of the scene/base motion period will be quantified and used as metrics of adaptability.
Investigators will use previously available data pre and post long-duration space flight from the Medical Requirement and Neuromapping study data set that are available through the Longitudinal Study of Astronaut Health (LSAH). These will include the Structural MRI scan, and Diffusion Tensor Imaging (DTI) scans. They will analyze the following measures for their potential as predictors of adaptive capacity: regional volumes of cerebellar lobules, white matter integrity of the cerebellum and the corticospinal tracts.
To determine if genetic markers predict change and also the ability to re-adapt after space flight, subjects will be asked to provide a saliva sample. The single nucleotide polymorphisms (SNPs) for catechol-o-methyltransferase (COMT), dopamine receptor 2 (DRD2), and alpha 2 adrenergic receptor will be determined through custom quantitative polymerase chain reaction (PCR) assays. SNPs will be investigated in the flight returning subjects. This module of the genotyping aspect of the proposal will be outsourced to Neogenomics Laboratories in Houston, Texas. Sequence data of individual samples for the four genes will be mapped to the reference genome and variant analysis will be performed by comparison to variant SNPs databases.
RESULTS:
This study is in progress. Results will be available at a later date.
