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NASA NTRS1978

Effect of prehatching weightlessness on adult fish behavior in dynamic environments

At 16-17 months of age, three groups of fish from the embryonated eggs in the ASTP killifish experiment were subjected to postflight tests consisting of rapidly changing environments. It was found that the group of fish with the least amount of development at orbital insertion (A-32) had a decreased rheotropism for both the moving background and the rotating water current tests when compared to ground control fish. Exposure to parabolic aircraft flight conditions revealed that the A-32 fish were less disoriented during zero gravity periods and were hypersensitive to high-gravity periods. These results suggested a modified vestibular competency due to a 9-d prehatching weightlessness exposure.

Hoffman, R. B.↗

NASA NTRS1983

The first dedicated life sciences mission - Spacelab 4

The details of the payload and the experiments in Spacelab 4, the first Spacelab mission dedicated entirely to the life sciences, are discussed. The payload of Spacelab 4, carried in the bay of the Shuttle Orbiter, consists of 25 tentatively selected investigations combined into a comprehensive integrated exploration of the effects of acute weightlessness on living systems. The payload contains complementary designs in the human and animal investigations in order to validate animal models of human physiology in weightlessness. Animals used as experimental subjects will include squirrel monkeys, laboratory rats, several species of plants, and frog eggs. The main scientific objectives of the investigations include the study of the acute cephalic fluid shift, cardiovascular adaptation to weightlessness, including postflight reductions in orthostatic tolerance and exercise capacity, and changes in vestibular function, including space motion sickness, associated with weightlessness. Other scientific objective include the study of red cell mass reduction, negative nitrogen balance, altered calcium metabolism, suppressed in vitro lymphocyte reactivity, gravitropism and photropism in plants, and fertilization and early development in frog eggs.

Cramer, D. R.↗

NASA NTRSDate not supplied

Functional Task Tests in Partial Gravity During Parabolic Flight

BACKGROUND Critical mission tasks required by crews immediately after landing on a planetary surface include walking, jumping, and egressing from a seat. Understanding how these functional tasks are performed in partial gravity such as on the moon or Mars is necessary to define effective and comprehensive countermeasure strategies for preserving crew performance during exploration-class missions. We propose to study the performance of these tasks during the partial gravity phases of parabolic flight. These tasks will be performed using the same equipment and procedures as those used with astronauts returning from spaceflight and with ground-based subjects after prolonged axial body unloading during bed rest (sensorimotor standard measures). HYPOTHESIS We hypothesize that partial gravity during parabolic flight will cause acute changes in vestibular, proprioceptive, and sensorimotor functions, and these changes will impact the performance of mission critical tasks such as standing, walking, and jumping. The largest changes in performance are expected at the lowest gravity level (0.25g) because subjects will no longer be able to use the gravitational reference for the perception of upright. Ultimately, this information could be used to assess performance risks and inform the design of countermeasures for NASA exploration-class human missions. METHODS Twelve subjects will be tested during three flights of 30 parabolas, including 10 parabolas at 0.25g, 10 parabolas at 0.5g, and 10 parabolas at 0.75g. Subjects also will perform tests in 1g between parabolas. The tasks will be the same as those tested on astronauts returning from spaceflight: sit-to-stand with obstacle walk, tandem rail balance, jump down, and recovery from fall. Measurements will include: (a) time to test completion (sit-to-stand with obstacle walk, recovery from fall); (b) time elapsed between the start of motion and the stabilization of upright posture (recovery from fall, jump down); (c) mean sway speed during quiet standing (recovery from fall, jump down); (d) changes in heart rate and blood pressure (recovery from fall); (e) balance time and torso accelerations (tandem rail balance); (f) cone of stability (jump down); and (g) severity of motion sickness symptoms. RELEVANCE Although gravitational dose-response curves have been obtained for some biochemical systems in animals, these dose-responses are unknown for most human physiologic systems. Our study will compare the outcomes of four functional task tests in 0.25g, 0.5g, 0.75g, and 1g with those previously obtained in ground-based subjects after prolonged axial body unloading and in astronauts immediately after spaceflight. These comparisons will help us understand the true extent of functional task performance deficits in partial gravity. The dose-response relationship between gravity level and task performance decrement also will help determining the gravity threshold for these functional tasks. ACKNOWLEDGEMENT This work is supported by the NASA’s Human Research Program Human Health Countermeasures Element.

T. R. Macaulay↗

NASA NTRS1981

Vestibular selection criteria development

The experimental elicitation of motion sickness using a short arm centrifuge or a rotating chair surrounded by a striped cylindrical enclosure failed to reveal any systematic group or consistent individual relationship between changes in heart rate, blood pressure, and body temperature and the appearance of symptoms of motion sickness. A study of the influence of vision on susceptability to motion sickness during sudden stop simulation shows that having the eyes open during any part of the sudden stop assessment is more stressful than having them closed throughout the test. Subjects were found to be highly susceptible to motion sickness when tested in free fall and in high force phases of flight. The effect of touch and pressure cues on body orientation during rotation and in parabolic flight are considered as sensory as well as motor adaptation.

Lackner, J. R.↗

NASA NTRS1999

A Methodology for Evaluating the Fidelity of Ground-Based Flight Simulators

An analytical and experimental investigation was undertaken to model the manner in which pilots perceive and utilize visual, proprioceptive, and vestibular cues in a ground-based flight simulator. The study was part of a larger research effort which has the creation of a methodology for determining flight simulator fidelity requirements as its ultimate goal. The study utilized a closed-loop feedback structure of the pilot/simulator system which included the pilot, the cockpit inceptor, the dynamics of the simulated vehicle and the motion system. With the exception of time delays which accrued in visual scene production in the simulator, visual scene effects were not included in this study. The NASA Ames Vertical Motion Simulator was used in a simple, single-degree of freedom rotorcraft bob-up/down maneuver. Pilot/vehicle analysis and fuzzy-inference identification were employed to study the changes in fidelity which occurred as the characteristics of the motion system were varied over five configurations i The data from three of the five pilots that participated in the experimental study were analyzed in the fuzzy inference identification. Results indicate that both the analytical pilot/vehicle analysis and the fuzzyinference identification can be used to reflect changes in simulator fidelity for the task examined.

Zeyada, Y.↗

NASA NTRS1999

A Methodology for Evaluating the Fidelity of Ground-Based Flight Simulators

An analytical and experimental investigation was undertaken to model the manner in which pilots perceive and utilize visual, proprioceptive, and vestibular cues in a ground-based flight simulator. The study was part of a larger research effort which has the creation of a methodology for determining flight simulator fidelity requirements as its ultimate goal. The study utilized a closed-loop feedback structure of the pilot/simulator system which included the pilot, the cockpit inceptor, the dynamics of the simulated vehicle and the motion system. With the exception of time delays which accrued in visual scene production in the simulator, visual scene effects were not included in this study. The NASA Ames Vertical Motion Simulator was used in a simple, single-degree of freedom rotorcraft bob-up/down maneuver. Pilot/vehicle analysis and fuzzy-inference identification were employed to study the changes in fidelity which occurred as the characteristics of the motion system were varied over five configurations. The data from three of the five pilots that participated in the experimental study were analyzed in the fuzzy-inference identification. Results indicate that both the analytical pilot/vehicle analysis and the fuzzy-inference identification can be used to reflect changes in simulator fidelity for the task examined.

Zeyada, Y.↗

NASA NTRS1999

Horizontal vestibuloocular reflex evoked by high-acceleration rotations in the squirrel monkey. I. Normal responses

The horizontal angular vestibuloocular reflex (VOR) evoked by high-frequency, high-acceleration rotations was studied in five squirrel monkeys with intact vestibular function. The VOR evoked by steps of acceleration in darkness (3,000 degrees /s(2) reaching a velocity of 150 degrees /s) began after a latency of 7.3 +/- 1.5 ms (mean +/- SD). Gain of the reflex during the acceleration was 14.2 +/- 5.2% greater than that measured once the plateau head velocity had been reached. A polynomial regression was used to analyze the trajectory of the responses to steps of acceleration. A better representation of the data was obtained from a polynomial that included a cubic term in contrast to an exclusively linear fit. For sinusoidal rotations of 0.5-15 Hz with a peak velocity of 20 degrees /s, the VOR gain measured 0.83 +/- 0.06 and did not vary across frequencies or animals. The phase of these responses was close to compensatory except at 15 Hz where a lag of 5.0 +/- 0.9 degrees was noted. The VOR gain did not vary with head velocity at 0.5 Hz but increased with velocity for rotations at frequencies of >/=4 Hz (0. 85 +/- 0.04 at 4 Hz, 20 degrees /s; 1.01 +/- 0.05 at 100 degrees /s, P < 0.0001). No responses to these rotations were noted in two animals that had undergone bilateral labyrinthectomy indicating that inertia of the eye had a negligible effect for these stimuli. We developed a mathematical model of VOR dynamics to account for these findings. The inputs to the reflex come from linear and nonlinear pathways. The linear pathway is responsible for the constant gain across frequencies at peak head velocity of 20 degrees /s and also for the phase lag at higher frequencies being less than that expected based on the reflex delay. The frequency- and velocity-dependent nonlinearity in VOR gain is accounted for by the dynamics of the nonlinear pathway. A transfer function that increases the gain of this pathway with frequency and a term related to the third power of head velocity are used to represent the dynamics of this pathway. This model accounts for the experimental findings and provides a method for interpreting responses to these stimuli after vestibular lesions.

NASA Program Biomedical Research and Countermeasur↗

NASA NTRS1975

Visual reaction times during prolonged angular acceleration parallel the subjective perception of rotation

The effect of prolonged angular acceleration on choice reaction time to an accelerating visual stimulus was investigated, with 10 commercial airline pilots serving as subjects. The pattern of reaction times during and following acceleration was compared with the pattern of velocity estimates reported during identical trials. Both reaction times and velocity estimates increased at the onset of acceleration, declined prior to the termination of acceleration, and showed an aftereffect. These results are inconsistent with the torsion-pendulum theory of semicircular canal function and suggest that the vestibular adaptation is of central origin.

Mattson, D. L.↗

NASA NTRS2014

Improving Early Adaptation Following Long Duration Spaceflight by Enhancing Vestibular Information

Crewmember adapted to the microgravity state may need to egress the vehicle within a few minutes for safety and operational reasons after g-transitions. The transition from one sensorimotor state to another consists of two main mechanisms: strategic and plastic-adaptive and have been demonstrated in astronauts returning after long duration space flight. Strategic modifications represent "early adaptation" -immediate and transitory changes in control that are employed to deal with short-term changes in the environment. If these modifications are prolonged then plastic-adaptive changes are evoked that modify central nervous system function, automating new behavioral responses. More importantly, this longer term adaptive recovery mechanism was significantly associated with their strategic ability to recover on the first day after return to Earth G. We are developing a method based on stochastic resonance (SR) to enhance information transfer by improving the brain's ability to detect vestibular signals especially when combined with balance training exercises for rapid improvement in functional skill, for standing and mobility. The countermeasure to improve post-flight balance and locomotor disturbances is a stimulus delivery system that is wearable/portable providing low imperceptible levels of white noise based binaural bipolar electrical stimulation of the vestibular system (stochastic vestibular stimulation, SVS). The techniques for improving signal detection using SVS may thus provide additional information to improve such strategic abilities and thus help in significantly reducing the number of days required to recover functional performance to preflight levels after long duration space flight. We have conducted a series of studies to document the efficacy of SVS stimulation on balance/locomotion tasks on unstable surfaces and motion tracking tasks during intra-vestibular system conflicts. In an initial study, we showed that SVS improved overall balance performance while standing on an unstable surface indicating that SVS may be sufficient to provide a comprehensive countermeasure approach for improving postural stability. In a second study, we showed that SVS improved locomotor performance on a treadmill mounted on an oscillating platform indicating that SVS may also be used to maximize locomotor performance during walking in unstable environments. In a third study, SVS was evaluated during an otolith-canal conflict scenario in a variable radius centrifuge at low frequency of oscillation (0.1 Hz) on both eye movements and perceptual responses (using a joystick) to track imposed oscillations. The variable radius centrifuge provides a selective tilting sensation that is detectable only by the otolith organs providing conflicting information from the canal organs of the vestibular system (intra-vestibular conflict). Results show that SVS significantly reduced the timing difference between both the eye movement responses as well as the perceptual tracking responses with respect to the imposed tilt sensations. These results indicate that SVS can improve performance in sensory conflict scenarios like that experienced during space flight. Such a SR countermeasure will act synergistically along with the pre-and in-flight adaptability training protocols providing an integrated, multi-disciplinary countermeasure capable of fulfilling multiple requirements making it a comprehensive and cost effective countermeasure approach to enhance sensorimotor capabilities following long-duration space flight.

Mulavara, Ajitkumar↗

NASA NTRS2015

The Effects of Long Duration Bed Rest as a Spaceflight Analogue on Resting State Sensorimotor Network Functional Connectivity and Neurocognitive Performance

Long duration spaceflight has been associated with detrimental alterations in human sensorimotor systems and neurocognitive performance. Prolonged exposure to a head-down tilt position during long duration bed rest can resemble several effects of the microgravity environment such as reduced sensory inputs, body unloading and increased cephalic fluid distribution. The question of whether microgravity affects other central nervous system functions such as brain functional connectivity and its relationship with neurocognitive performance is largely unknown, but of potential importance to the health and performance of astronauts both during and post-flight. The aims of the present study are 1) to identify changes in sensorimotor resting state functional connectivity that occur with extended bed rest exposure, and to characterize their recovery time course; 2) to evaluate how these neural changes correlate with neurocognitive performance. Resting-state functional magnetic resonance imaging (rsfMRI) data were collected from 17 male participants. The data were acquired through the NASA bed rest facility, located at the University of Texas Medical Branch (Galveston, TX). Participants remained in bed with their heads tilted down six degrees below their feet for 70 consecutive days. RsfMRI data were obtained at seven time points: 7 and 12 days before bed rest; 7, 50, and 65 days during bed rest; and 7 and 12 days after bed rest. Functional connectivity magnetic resonance imaging (fcMRI) analysis was performed to measure the connectivity of sensorimotor networks in the brain before, during, and post-bed rest. We found a decrease in left putamen connectivity with the pre- and post-central gyri from pre bed rest to the last day in bed rest. In addition, vestibular cortex connectivity with the posterior cingulate cortex decreased from pre to post bed rest. Furthermore, connectivity between cerebellar right superior posterior fissure and other cerebellar regions decreased from pre bed rest to the last day in bed rest. In contrast, connectivity within the default mode network remained stable over the course of bed rest. We also utilized a battery of behavioral measures including spatial working memory tasks and measures of functional mobility and balance. These behavioral measurements were collected before, during, and after bed rest. We will report the preliminary findings of correlations observed between brain functional connectivity and behavioral performance changes. Our results suggest that sensorimotor brain networks exhibit decoupling with extended periods of reduced usage. The findings from this study could aid in the understanding and future design of targeted countermeasures to alleviate the detrimental health and neurocognitive effects of long-duration spaceflight.

Cassady, K.↗

NASA NTRS1993

Contribution of irregular semicircular canal afferents to the horizontal vestibuloocular response during constant velocity rotation

1. The effects of constant anodal currents (100 microA) delivered bilaterally to both labyrinths on the horizontal vestibuloocular response (VOR) were studied in squirrel monkeys during steps of angular velocity in the dark. We report that bilateral anodal currents decreased eye velocity approximately 30-50% during the period of galvanic stimulation without a change in the time constant of VOR. The decrease in eye velocity, present during steps of angular velocity, was not observed during sinusoidal head rotation at 0.2, 0.5, and 1 Hz. The results suggest that responses from irregular vestibular afferents influence VOR amplitude during constant velocity rotation.

NASA Discipline Neuroscience↗

NASA NTRS1987

Results of the Life Sciences DSOs Conducted Aboard the Space Shuttle 1981-1986

Results are presented for a number of life sciences investigations sponsored by the Space Biomedical Research Institute at the NASA Lyndon B. Johnson Space Center and conducted as Detailed Supplementary Objectives (DSOs) on Space Shuttle flights between 1981 and 1986. An introduction and a description of the DSO program are followed by summary reports on the investigations. Reports are grouped into the following disciplines: Biochemistry and Pharmacology, Cardiovascular Effects and Fluid Shifts, Equipment Testing and Experiment Verification, Microbiology, Space Motion Sickness, and Vision. In the appendix, the status of every medical/life science DSO is presented in graphical form, which enables the flight history, the number of subjects tested, and the experiment results to be reviewed at a glance.

Vestibular Research↗

NASA NTRS2003

Visual and Vestibular Determinants of Perceived Eye-Level

Both gravitational and optical sources of stimulation combine to determine the perceived elevations of visual targets. The ways in which these sources of stimulation combine with one another in operational aeronautical environments are critical for pilots to make accurate judgments of the relative altitudes of other aircraft and of their own altitude relative to the terrain. In a recent study, my colleagues and I required eighteen observers to set visual targets at their apparent horizon while they experienced various levels of G(sub z) in the human centrifuge at NASA-Ames Research Center. The targets were viewed in darkness and also against specific background optical arrays that were oriented at various angles with respect to the vertical; target settings were lowered as Gz was increased; this effect was reduced when the background optical array was visible. Also, target settings were displaced in the direction that the background optical array was pitched. Our results were attributed to the combined influences of otolith-oculomotor mechanisms that underlie the elevator illusion and visual-oculomotor mechanisms (optostatic responses) that underlie the perceptual effects of viewing pitched optical arrays that comprise the background. In this paper, I present a mathematical model that describes the independent and combined effects of G(sub z) intensity and the orientation and structure of background optical arrays; the model predicts quantitative deviations from normal accurate perceptions of target localization under a variety of conditions. Our earlier experimental results and the mathematical model are described in some detail, and the effects of viewing specific optical arrays under various gravitational-inertial conditions encountered in aeronautical environments are discussed.

Cohen, Malcolm Martin↗

NASA NTRS1987

The influence of gravitoinertial force level on oculomotor and perceptual responses to sudden stop stimulation

The goal of this investigation was to determine whether the vestibular response to vertical, z-axis body rotation in the dark is influenced by the magnitude of gravitoinertial force. The parameters measured were the nystagmus and the duration of illusory self-motion elicited in blindfolded subjects by cessation of such rotation during the free-fall, high, and terrestrial force phases of parabolic flight maneuvers. The pattern of findings is consistent with the responses that were observed earlier to constant levels of Coriolis cross-coupled stimulation during parabolic flight maneuvers both in terms of the mode of nystagmus suppression and the effect of G-level.

Dizio, Paul↗

NASA NTRS1998

Swimming kinematics and respiratory behaviour of Xenopus laevis larvae raised in altered gravity

We examined the respiratory behaviours and swimming kinematics of Xenopus laevis tadpoles hatched in microgravity (Space Shuttle), simulated microgravity (clinostat) and hypergravity (3 g centrifuge). All observations were made in the normal 1 g environment. Previous research has shown that X. laevis raised in microgravity exhibit abnormalities in their lungs and vestibular system upon return to 1 g. The tadpoles raised in true microgravity exhibited a significantly lower tailbeat frequency than onboard 1 g centrifuge controls on the day of landing (day0), but this behaviour normalized within 9 days. The two groups did not differ significantly in buccal pumping rates. Altered buoyancy in the space-flight microgravity tadpoles was indicated by an increased swimming angle on the day after landing (day1). Tadpoles raised in simulated microgravity differed to a greater extent in swimming behaviours from their 1 g controls. The tadpoles raised in hypergravity showed no substantive effects on the development of swimming or respiratory behaviours, except swimming angle. Together, these results show that microgravity has a transient effect on the development of locomotion in X. laevis tadpoles, most notably on swimming angle, indicative of stunted lung development. On the basis of the behaviours we studied, there is no indication of neuromuscular retardation in amphibians associated with embryogenesis in microgravity.

Flight Experiment↗

NASA NTRS1994

Evidence against a hypothesis of vestibular efferent function

Efferent stimulation and nicotinic agonists can either decrease or increase the frequency of occurrence of EPSPs recorded from VIIIth nerve afferents in the frog. It has been hypothesized that the distribution of hair cell resting membrane potentials overlaps the equilibrium potential dictated by the nicotinic-gated channels on the hair cells. Nicotinic mediated increases in EPSP frequency would then be due to depolarization of hair cells that were more hyperpolarized at rest, while decreases in EPSP frequency would be due to hyperpolarization of hair cells more depolarized at rest. In order to test this hypothesis, while recording from afferents which showed an increase in EPSP frequency due to bath application of the nicotinic agonist DMPP (1,1-dimethyl-4-phenylpiperizinium iodide), hair cells were depolarized with 10 mM K+ in the bath, and then the effects of DMPP on EPSP frequency were assessed. In this situation, DMPP still increased EPSP frequency, suggesting that the equilibrium potential for the nicotinic-gated channel was much more positive than the resting potentials of the hair cells. An alternative hypothesis then seems likely, that the nicotinic receptors on hair cells are able to activate different iontophores that result in either hair cell depolarization or hyperpolarization, dependent upon which iontophore predominates in the hair cells innervating a particular afferent.

NASA Discipline Neuroscience↗

NASA NTRS1979

Optokinetic motion sickness - Attenuation of visually-induced apparent self-rotation by passive head movements

An experimental study was conducted on seven normal subjects to evaluate the effectiveness of passive head movements in suppressing the optokinetically-induced illusory self-rotation. Visual simulation was provided by a servo-controlled optokinetic drum. Each subject participated in two experimental sessions. In one condition, the subject's head remained stationary while he gazed passively at a moving stripe pattern. In the other, he gazed passively and relaxed his neck muscles while his head was rotated from side to side. It appears that suppression of optokinetically-induced illusory self-rotation with passive head movements results from the operation of a spatial constancy mechanism interrelating visual, vestibular, and kinesthetic information on ongoing body orientation. The results support the view that optokinetic 'motion sickness' is related, at least in part, to an oculomotor disturbance rather than a visually triggered disturbance of specifically vestibular etiology.

Teixeira, R. A.↗

NASA NTRS2014

Focal Gray Matter Plasticity as a Function of Long Duration Head Down Tilted Bed Rest: Preliminary Results

Long duration spaceflight (i.e., 22 days or longer) has been associated with changes in sensorimotor systems, resulting in difficulties that astronauts experience with posture control, locomotion, and manual control. The microgravity environment is an important causal factor for spaceflight induced sensorimotor changes. Whether these sensorimotor changes are solely related to peripheral changes from reduced vestibular stimulation, body unloading, body fluid shifts or that they may be related to structural and functional brain changes is yet unknown. However, a recent study reported associations between microgravity and flattening of the posterior eye globe and protrusion of the optic nerve [1] possibly as the result of increased intracranial pressure due to microgravity induced bodily fluid shifts [3]. Moreover, elevated intracranial pressure has been related to white matter microstructural damage [2]. Thus, it is possible that spaceflight may affect brain structure and thereby cognitive functioning. Long duration head down tilt bed rest has been suggested as an exclusionary analog to study microgravity effects on the sensorimotor system [4]. Bed rest mimics microgravity in body unloading and bodily fluid shifts. In consideration of the health and performance of crewmembers both in- and post-flight, we are conducting a prospective longitudinal 70-day bed rest study as an analog to investigate the effects of microgravity on brain structure [5]. Here we present results of the first six subjects. Six subjects were assessed at 12 and 7 days before-, at 7, 30, and ~70 days in-, and at 8 and 12 days post 70 days of bed rest at the NASA bed rest facility in UTMB, Galveston, TX, USA. At each time point structural MRI scans (i.e., high resolution T1-weighted imaging and Diffusion Tensor Imaging (DTI)) were obtained using a 3T Siemens scanner. Focal changes over time in gray matter density were assessed using the voxel based morphometry 8 (VBM8) toolbox under SPM. Longitudinal processing in VBM8 includes linear registration of each scan to the mean of the subject and subsequently transforming all scans in to MNI space by applying the warp from the mean subject to MNI to the individual gray matter segmentations. Modulation was applied so that all images represented the volume of the original structure in native space. Voxel wise analysis was carried out on the gray matter images after smoothing, using a flexible factorial design with family wise error correction. Focal changes in white matter microstructural integrity were assessed using tract based spatial statistics (TBSS) as part of FMRIB software library (FSL). TBSS registers all DTI scans to standard space. It subsequently creates a study specific white matter skeleton of the major white matter tracts. For each subject, for each DTI metric (i.e. fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), and radial diffusivity (RD)), the maximum value in a line perpendicular to the skeleton tract is projected to the skeleton. Non-parametric permutation based t-tests and ANOVA's were used for voxel-wise comparison of the skeletons. For both VBM and TBSS, comparison of pre bed rest measurements did not show significant differences. VBM analysis revealed decreased gray matter density in bilateral areas including the frontal medial cortex, the insular cortex and the caudate (see Figure) from 'pre to in bed rest'. Over the same time period, there was an increase in gray matter density in the cerebellum, occipital-, and parietal cortex, including the precuneus (see Figure). The majority of these changes did not recover from 'during to post bed rest'. TBSS analysis did not reveal significant changes in white matter microstructural integrity after correction for multiple comparisons. Uncorrected analyses (p<.015) revealed an increase in RD in the cerebellum and brainstem from pre bed rest to the first week in bed rest that did not recover post bed rest. Extended bed rest, which is an analog for microgravity, can result in gray matter changes and potentially in microstructural white matter changes in areas that are important for neuro motor behavior and cognition. These changes did not recover at two weeks post bed rest. Whether the effects of bed rest wear off at longer times post bed rest, and if they are associated with behavior are important questions that warrant further research.

Koppelmans, V.↗