4 research outputs found
Neural Working Memory Changes During a Spaceflight Analog With Elevated Carbon Dioxide: A Pilot Study
Spaceflight missions to the International Space Station (ISS) expose astronauts to
microgravity, radiation, isolation, and elevated carbon dioxide (COâ‚‚), among other
factors. Head down tilt bed rest (HDBR) is an Earth-based analog for spaceflight used to
study body unloading, fluid shifts, and other factors unrelated to gravitational changes.
While in space, astronauts need to use mental rotation strategies to facilitate their
adaptation to the ISS environment. Therefore, spatial working memory is essential for
crewmember performance. Although the effects of HDBR on spatial working memory
have recently been studied, the results are still inconclusive. Here, we expand upon
past work and examine the effects of HDBR with elevated COâ‚‚ (HDBR + COâ‚‚) on
brain activation patterns during spatial working memory performance. In addition,
we compare brain activation between 30 days of HDBR + COâ‚‚ and 70 days of
HDBR to test the isolated effect of COâ‚‚. Eleven subjects (6 males, 5 females; mean
age = 34 ± 8 years) underwent six functional magnetic resonance imaging (fMRI)
sessions pre-, during, and post-HDBR + COâ‚‚. During the HDBR + COâ‚‚ intervention,
we observed decreasing activation in the right middle frontal gyrus and left regions of
the cerebellum, followed by post-intervention recovery. We detected several correlations
between brain and behavioral slopes of change with the HDBR + COâ‚‚ intervention.
For example, greater increases in activation in frontal, temporal and parietal regions
were associated with larger spatial working memory improvements. Comparing the
HDBR + COâ‚‚ group to data from our previous 70-day HDBR study, we found greater
decreases in activation in the right hippocampus and left inferior temporal gyrus for
the HDBR + COâ‚‚ group over the course of the intervention. Together, these findings
increase our understanding of the neural mechanisms of HDBR, elevated levels of COâ‚‚
and spaceflight-related changes in spatial working memory performance
The Impact of 6 and 12 Months in Space on Human Brain Structure and Intracranial Fluid Shifts
As plans develop for Mars missions, it is important to understand how long-duration spaceflight impacts brain health. Here
we report how 12-month (n = 2 astronauts) versus 6-month (n = 10 astronauts) missions impact brain structure and fluid
shifts. We collected MRI scans once before flight and four times after flight. Astronauts served as their own controls; we
evaluated pre- to postflight changes and return toward preflight levels across the 4 postflight points. We also provide data to
illustrate typical brain changes over 7 years in a reference dataset. Twelve months in space generally resulted in larger
changes across multiple brain areas compared with 6-month missions and aging, particularly for fluid shifts. The majority of
changes returned to preflight levels by 6 months after flight. Ventricular volume substantially increased for 1 of the
12-month astronauts (left: +25%, right: +23%) and the 6-month astronauts (left: 17 ± 12%, right: 24 ± 6%) and exhibited little
recovery at 6 months. Several changes correlated with past flight experience; those with less time between subsequent missions had larger preflight ventricles and smaller ventricular volume increases with flight. This suggests that spaceflight-induced
ventricular changes may endure for long periods after flight. These results provide insight into brain changes that occur with longduration spaceflight and demonstrate the need for closer study of fluid shift
Neural Correlates of Vestibular Processing During a Spaceflight Analog With Elevated Carbon Dioxide (COâ‚‚): A Pilot Study
Astronauts return to Earth from spaceflight missions with impaired mobility and balance;
recovery can last weeks postflight. This is due in large part to the altered vestibular
signaling and sensory reweighting that occurs in microgravity. The neural mechanisms
of spaceflight-induced vestibular changes are not well understood. Head-down-tilt bed
rest (HDBR) is a common spaceflight analog environment that allows for study of
body unloading, fluid shifts, and other consequences of spaceflight. Subjects in this
context still show vestibular changes despite being in Earth’s gravitational environment,
potentially due to sensory reweighting. Previously, we found evidence of sensory
reweighting and reduced neural efficiency for vestibular processing in subjects who
underwent a 70-day HDBR intervention. Here we extend this work by evaluating the
impact of HDBR paired with elevated carbon dioxide (COâ‚‚) to mimic International
Space Station conditions on vestibular neural processing. Eleven participants (6 males,
34 ± 8 years) completed 30 days of HDBR combined with 0.5% atmospheric CO₂
(HDBR + COâ‚‚). Participants underwent six functional magnetic resonance imaging
(fMRI) sessions pre-, during, and post- HDBR + COâ‚‚ while we measured brain activity
in response to pneumatic skull taps (a validated method of vestibular stimulation). We
also measured mobility and balance performance several times before and after the
intervention. We found support for adaptive neural changes within the vestibular system
during bed rest that subsequently recovered in several cortical and cerebellar regions.
Further, there were multiple brain regions where greater pre- to post- deactivation was
associated with reduced pre- to post- balance declines. That is, increased deactivation
of certain brain regions associated with better balance post-HDBR + COâ‚‚. We also
found that, compared to HDBR alone (n = 13 males; 29 ± 3 years) HDBR + CO₂ is
associated with greater increases in activation of multiple frontal, parietal, and temporal
regions during vestibular stimulation. This suggests interactive or additive effects of bed
rest and elevated COâ‚‚. Finally, we found stronger correlations between pre- to postHDBR + COâ‚‚ brain changes and dependence on the visual system during balance
for subjects who developed signs of Spaceflight-Associated Neuro-ocular Syndrome
Frontiers in Systems Neuroscience | www.frontiersin.org 1 January 2020 | Volume 13 | Article 80Hupfeld et al. Neural Vestibular Processing With HDBR + COâ‚‚
(SANS). Together, these findings have clear implications for understanding the neural
mechanisms of bed rest and spaceflight-related changes in vestibular processing, as
well as adaptation to altered sensory inputs
Impacts of spaceflight experience on human brain structure
Abstract Spaceflight induces widespread changes in human brain morphology. It is unclear if these brain changes differ with varying mission duration or spaceflight experience history (i.e., novice or experienced, number of prior missions, time between missions). Here we addressed this issue by quantifying regional voxelwise changes in brain gray matter volume, white matter microstructure, extracellular free water (FW) distribution, and ventricular volume from pre- to post-flight in a sample of 30 astronauts. We found that longer missions were associated with greater expansion of the right lateral and third ventricles, with the majority of expansion occurring during the first 6Â months in space then appearing to taper off for longer missions. Longer inter-mission intervals were associated with greater expansion of the ventricles following flight; crew with less than 3Â years of time to recover between successive flights showed little to no enlargement of the lateral and third ventricles. These findings demonstrate that ventricle expansion continues with spaceflight with increasing mission duration, and inter-mission intervals less than 3Â years may not allow sufficient time for the ventricles to fully recover their compensatory capacity. These findings illustrate some potential plateaus in and boundaries of human brain changes with spaceflight