Structural Brain Changes following Long-Term 6° Head-Down Tilt Bed Rest as an Analog for Spaceflight

Roberts, Donna R.; Zhu, Xiaolong; Tabesh, Ali; Duffy, E.W.; Ramsey, David; Brown, Truman R.

doi:10.3174/ajnr.a4406

Cited by 65 publications

(46 citation statements)

References 18 publications

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“…As previously mentioned, HDBR studies have reported that gait and balance declines with HDBR are related to brain structural changes 5, 7, 8 and functional connectivity changes 9 . Moreover, a case study of one astronaut reported spaceflight-induced changes in resting state functional connectivity between the motor cortex and the cerebellum 4 .…”

Section: Introductionmentioning

confidence: 92%

“…HDBR studies serve as a microgravity analog because they mimic the headward fluid shifts and body unloading of spaceflight 6 . Recent HDBR studies from our lab as well as others utilizing anatomical functional and diffusion MRI showed that HDBR leads to gray matter increases in posterior parietal areas and decreases in fronto-temporal brain areas 5, 7, 8 , changes in white matter microstructure 7 , changes in the functional connectivity of motor, somatosensory, and vestibular areas of the brain 9 , brain activation changes in motor regions under dual tasking conditions 10 , and functional deterioration of gait and balance 11 . Many of these changes appear to reflect neuroplasticity.…”

Section: Introductionmentioning

confidence: 95%

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Intracranial Fluid Redistribution But No White Matter Microstructural Changes During a Spaceflight Analog

Koppelmans

Pasternak

Bloomberg

et al. 2017

Sci Rep

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The neural correlates of spaceflight-induced sensorimotor impairments are unknown. Head down-tilt bed rest (HDBR) serves as a microgravity analog because it mimics the headward fluid shift and axial body unloading of spaceflight. We investigated focal brain white matter (WM) changes and fluid shifts during 70 days of 6° HDBR in 16 subjects who were assessed pre (2x), during (3x), and post-HDBR (2x). Changes over time were compared to those in control subjects (n = 12) assessed four times over 90 days. Diffusion MRI was used to assess WM microstructure and fluid shifts. Free-Water Imaging was used to quantify distribution of intracranial extracellular free water (FW). Additionally, we tested whether WM and FW changes correlated with changes in functional mobility and balance measures. HDBR resulted in FW increases in fronto-temporal regions and decreases in posterior-parietal regions that largely recovered by two weeks post-HDBR. WM microstructure was unaffected by HDBR. FW decreases in the post-central gyrus and precuneus correlated negatively with balance changes. We previously reported that gray matter increases in these regions were associated with less HDBR-induced balance impairment, suggesting adaptive structural neuroplasticity. Future studies are warranted to determine causality and underlying mechanisms.

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Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 95%

Intracranial Fluid Redistribution But No White Matter Microstructural Changes During a Spaceflight Analog

Koppelmans

Pasternak

Bloomberg

et al. 2017

Sci Rep

View full text Add to dashboard Cite

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“…69 They found several structural changes due to the simulated microgravity, with the most prominent one being the fact that the brain underwent an upward shift and posterior rotation relative to skull. Furthermore, they found a correlation between the posterior brain rotation and ventricular volume.…”

Section: Overview and Critical Appraisal Of The Current Literaturementioning

confidence: 99%

“…60 However, conclusions in regards to spaceflight need to be made carefully by both the indirect comparison of space analogs to actual spaceflight 56,61,63,65,66,68,71,72 and the small sample size in some of the current studies. 57,60,69 …”

Section: Overview and Critical Appraisal Of The Current Literaturementioning

confidence: 99%

“…57,69 Previous spaceflight studies have already shown that inter-subject variability in space travelers is quite high, also for other physiological processes such as sensorimotor adaptation 75,76 and vestibular and otolith deconditioning. 77,78 High inter-subject variability is therefore a feature that should be kept in mind when analyzing and interpreting spaceflight studies, in particular with regards to studies on spaceflight-induced neuroplasticity.…”

Section: General Difficulties and Limitations Of Space Researchmentioning

confidence: 99%

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Spaceflight-induced neuroplasticity in humans as measured by MRI: what do we know so far?

et al. 2017

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Space travel poses an enormous challenge on the human body; microgravity, ionizing radiation, absence of circadian rhythm, confinement and isolation are just some of the features associated with it. Obviously, all of the latter can have an impact on human physiology and even induce detrimental changes. Some organ systems have been studied thoroughly under space conditions, however, not much is known on the functional and morphological effects of spaceflight on the human central nervous system. Previous studies have already shown that central nervous system changes occur during and after spaceflight in the form of neurovestibular problems, alterations in cognitive function and sensory perception, cephalic fluid shifts and psychological disturbances. However, little is known about the underlying neural substrates. In this review, we discuss the current limited knowledge on neuroplastic changes in the human central nervous system associated with spaceflight (actual or simulated) as measured by magnetic resonance imaging-based techniques. Furthermore, we discuss these findings as well as their future perspectives, since this can encourage future research into this delicate and intriguing aspect of spaceflight. Currently, the literature suffers from heterogeneous experimental set-ups and therefore, the lack of comparability of findings among studies. However, the cerebellum, cortical sensorimotor and somatosensory areas and vestibular-related pathways seem to be involved across different studies, suggesting that these brain regions are most affected by (simulated) spaceflight. Extending this knowledge is crucial, especially with the eye on long-duration interplanetary missions (e.g. Mars) and space tourism.

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Spaceflight-Associated Brain White Matter Microstructural Changes and Intracranial Fluid Redistribution

et al. 2019

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IMPORTANCE Spaceflight results in transient balance declines and brain morphologic changes; to our knowledge, the effect on brain white matter as measured by diffusion magnetic resonance imaging (dMRI), after correcting for extracellular fluid shifts, has not been examined. OBJECTIVE To map spaceflight-induced intracranial extracellular free water (FW) shifts and to evaluate changes in brain white matter diffusion measures in astronauts. DESIGN, SETTING AND PARTICIPANTS We performed retrospective, longitudinal analyses on dMRI data collected between 2010 and 2015. Of the 26 astronauts' dMRI scans released by the National Aeronautics and Space Administration Lifetime Surveillance of Astronaut Health, 15 had both preflight and postflight dMRI scans and were included in the final analyses. Data were analyzed between 2015 and 2018. INTERVENTIONS OR EXPOSURES Seven astronauts completed a space shuttle mission (Յ30 days) and 8 completed a long-duration International Space Station mission (Յ200 days). MAIN OUTCOMES AND MEASURES The dMRI scans were acquired for clinical monitoring; in this retrospective analysis, we analyzed brain FW and white matter diffusion metrics corrected for FW. We also obtained scores from computerized dynamic posturography tests of balance to assess brain-behavior associations. RESULTS Of the 15 astronauts included, the median (SD) age was 47.2 (1.5) years; 12 were men, and 3 were women. We found a significant, widespread increase in FW volume in the frontal, temporal, and occipital lobes from before spaceflight to after spaceflight. There was also a significant decrease in FW in the posterior aspect of the vertex. All FW changes were significant and ranged from approximately 2.5% to 4.0% across brain regions. We observed white matter changes in the right superior and inferior longitudinal fasciculi, the corticospinal tract, and cerebellar peduncles. All white matter changes were significant and ranged from approximately 0.75% to 1.25%. Spaceflight mission duration was associated with cerebellar white matter change, and white matter changes in the superior longitudinal fasciculus were associated with the balance changes seen in the astronauts from before spaceflight to after spaceflight. CONCLUSIONS AND RELEVANCE Free water redistribution with spaceflight likely reflects headward fluid shifts occurring in microgravity as well as an upward shift of the brain within the skull. White matter changes were of a greater magnitude than those typically seen during the same period with healthy aging. Future, prospective assessments are required to better understand the recovery time and behavioral consequences of these brain changes.

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Structural Brain Changes following Long-Term 6° Head-Down Tilt Bed Rest as an Analog for Spaceflight

Cited by 65 publications

References 18 publications

Intracranial Fluid Redistribution But No White Matter Microstructural Changes During a Spaceflight Analog

Intracranial Fluid Redistribution But No White Matter Microstructural Changes During a Spaceflight Analog

Spaceflight-induced neuroplasticity in humans as measured by MRI: what do we know so far?

Spaceflight-Associated Brain White Matter Microstructural Changes and Intracranial Fluid Redistribution

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