43 research outputs found
Head Down Tilt Bed Rest Plus Elevated CO2 as a Spaceflight Analog: Effects on Cognitive and Sensorimotor Performance
Long duration head down tilt bed rest (HDBR) has been widely used as a spaceflight
analog environment to understand the effects of microgravity on human physiology
and performance. Reports have indicated that crewmembers onboard the International
Space Station (ISS) experience symptoms of elevated CO2 such as headaches at lower
levels of CO2 than levels at which symptoms begin to appear on Earth. This suggests
there may be combinatorial effects of elevated CO2 and the other physiological effects
of microgravity including headward fluid shifts and body unloading. The purpose of the
current study was to investigate these effects by evaluating the impact of 30 days of 6âŠ
HDBR and 0.5% CO2 (HDBR C CO2) on mission relevant cognitive and sensorimotor
performance. We found a facilitation of processing speed and a decrement in functional
mobility for subjects undergoing HDBR C CO2 relative to our previous study of HDBR
in ambient air. In addition, nearly half of the participants in this study developed signs
of Spaceflight Associated Neuro-ocular Syndrome (SANS), a constellation of ocular
structural and functional changes seen in approximately one third of long duration
astronauts. This allowed us the unique opportunity to compare the two subgroups. We
found that participants who exhibited signs of SANS became more visually dependent
and shifted their speed-accuracy tradeoff, such that they were slower but more
accurate than those that did not incur ocular changes. These small subgroup findings
suggest that SANS may have an impact on mission relevant performance inflight via
sensory reweighting.
NEW AND NOTEWORTHY
We examined the effects of long duration head down tilt bed rest coupled with
elevated CO2 as a spaceflight analog environment on human cognitive and sensorimotor
performance. We found enhancements in processing speed and declines in functional
Frontiers in Human Neuroscience | www.frontiersin.org 1 October 2019 | Volume 13 | Article 355Lee et al. Spaceflight Analog Effects on Behavior
mobility. A subset of participants exhibited signs of Spaceflight Associated Neuroocular Syndrome (SANS), which affects approximately one in three astronauts. These
individuals increased their visual reliance throughout the intervention in comparison to
participants who did not show signs of SAN
Enhancement of Otolith Specific Ocular Responses Using Vestibular Stochastic Resonance
Introduction: Astronauts experience disturbances in sensorimotor function after spaceflight during the initial introduction to a gravitational environment, especially after long-duration missions. Our goal is to develop a countermeasure based on vestibular stochastic resonance (SR) that could improve central interpretation of vestibular input and mitigate these risks. SR is a mechanism by which noise can assist and enhance the response of neural systems to relevant, imperceptible sensory signals. We have previously shown that imperceptible electrical stimulation of the vestibular system enhances balance performance while standing on an unstable surface. Methods: Eye movement data were collected from 10 subjects during variable radius centrifugation (VRC). Subjects performed 11 trials of VRC that provided equivalent tilt stimuli from otolith and other graviceptor input without the normal concordant canal cues. Bipolar stochastic electrical stimulation, in the range of 0-1500 microamperes, was applied to the vestibular system using a constant current stimulator through electrodes placed over the mastoid process behind the ears. In the VRC paradigm, subjects were accelerated to 216 deg./s. After the subjects no longer sensed rotation, the chair oscillated along a track at 0.1 Hz to provide tilt stimuli of 10 deg. Eye movements were recorded for 6 cycles while subjects fixated on a target in darkness. Ocular counter roll (OCR) movement was calculated from the eye movement data during periods of chair oscillations. Results: Preliminary analysis of the data revealed that 9 of 10 subjects showed an average increase of 28% in the magnitude of OCR responses to the equivalent tilt stimuli while experiencing vestibular SR. The signal amplitude at which performance was maximized was in the range of 100-900 microamperes. Discussion: These results indicate that stochastic electrical stimulation of the vestibular system can improve otolith specific responses. This will have a significant impact on development of vestibular SR delivery systems to aid recovery of function in astronauts after long-duration spaceflight or in people with balance disorders
Using low levels of stochastic vestibular stimulation to improve locomotor stability
Low levels of bipolar binaural white noise based imperceptible stochastic electrical stimulation to the vestibular system (stochastic vestibular stimulation, SVS) have been shown to improve stability during balance tasks in normal, healthy subjects by facilitating enhanced information transfer using stochastic resonance (SR) principles. We hypothesize that detection of time-critical sub-threshold sensory signals using low levels of bipolar binaural SVS based on SR principles will help improve stability of walking during support surface perturbations. In the current study 13 healthy subjects were exposed to short continuous support surface perturbations for 60 s while walking on a treadmill and simultaneously viewing perceptually matched linear optic flow. Low levels of bipolar binaural white noise based SVS were applied to the vestibular organs. Multiple trials of the treadmill locomotion test were performed with stimulation current levels varying in the range of 0â1500 ÎŒA, randomized across trials. The results show that subjects significantly improved their walking stability during support surface perturbations at stimulation levels with peak amplitude predominantly in the range of 100â500 ÎŒA consistent with the SR phenomenon. Additionally, objective perceptual motion thresholds were measured separately as estimates of internal noise while subjects sat on a chair with their eyes closed and received 1 Hz bipolar binaural sinusoidal electrical stimuli. The optimal improvement in walking stability was achieved on average with peak stimulation amplitudes of approximately 35% of perceptual motion threshold. This study shows the effectiveness of using low imperceptible levels of SVS to improve dynamic stability during walking on a laterally oscillating treadmill via the SR phenomenon
Study protocol to examine the effects of spaceflight and a spaceflight analog on neurocognitive performance: extent, longevity, and neural bases
Abstract
Background
Long duration spaceflight (i.e., 22Â 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 spaceflight also affects other central nervous system functions such as cognition is yet largely unknown, but of importance in consideration of the health and performance of crewmembers both in- and post-flight. We are therefore conducting a controlled prospective longitudinal study to investigate the effects of spaceflight on the extent, longevity and neural bases of sensorimotor and cognitive performance changes. Here we present the protocol of our study.
Methods/design
This study includes three groups (astronauts, bed rest subjects, ground-based control subjects) for which each the design is single group with repeated measures. The effects of spaceflight on the brain will be investigated in astronauts who will be assessed at two time points pre-, at three time points during-, and at four time points following a spaceflight mission of six months. To parse out the effect of microgravity from the overall effects of spaceflight, we investigate the effects of seventy days head-down tilted bed rest. Bed rest subjects will be assessed at two time points before-, two time points during-, and three time points post-bed rest. A third group of ground based controls will be measured at four time points to assess reliability of our measures over time. For all participants and at all time points, except in flight, measures of neurocognitive performance, fine motor control, gait, balance, structural MRI (T1, DTI), task fMRI, and functional connectivity MRI will be obtained. In flight, astronauts will complete some of the tasks that they complete pre- and post flight, including tasks measuring spatial working memory, sensorimotor adaptation, and fine motor performance. Potential changes over time and associations between cognition, motor-behavior, and brain structure and function will be analyzed.
Discussion
This study explores how spaceflight induced brain changes impact functional performance. This understanding could aid in the design of targeted countermeasures to mitigate the negative effects of long-duration spaceflight.http://deepblue.lib.umich.edu/bitstream/2027.42/112560/1/12883_2013_Article_922.pd
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
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 Earthâs 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 COâ
(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 + COâ 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
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
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<p>Astronauts exposed to microgravity face sensorimotor challenges affecting balance control when readapting to Earth's gravity upon return from spaceflight. Small amounts of electrical noise applied to the vestibular system have been shown to improve balance control during standing and walking under discordant sensory conditions in healthy subjects, likely by enhancing information transfer through the phenomenon of stochastic resonance. The purpose of this study was to test the hypothesis that imperceptible levels of stochastic vestibular stimulation (SVS) could improve short-term adaptation to a locomotor task in a novel sensory discordant environment. Healthy subjects (14 males, 10 females, age = 28.7 ± 5.3 years, height = 167.2 ± 9.6 cm, weight = 71.0 ± 12.8 kg) were tested for perceptual thresholds to sinusoidal currents applied across the mastoids. Subjects were then randomly and blindly assigned to an SVS group receiving a 0â30 Hz Gaussian white noise electrical stimulus at 50% of their perceptual threshold (stim) or a control group receiving zero stimulation during Functional Mobility Tests (FMTs), nine trials of which were done under conditions of visual discordance (wearing up/down vision reversing goggles). Time to complete the course (TCC) was used to test the effect of SVS between the two groups across the trials. Adaptation rates from the normalized TCCs were also compared utilizing exponent values of power fit trendline equations. A one-tailed independent-samples t-test indicated these adaptation rates were significantly faster in the stim group (n = 12) than the control (n = 12) group [t<sub>(16.18)</sub> = 2.00, p = 0.031]. When a secondary analysis was performed comparing ârespondersâ (subjects who showed faster adaptation rates) of the stim (n = 7) group to the control group (n = 12), independent-samples t-tests revealed significantly faster trial times for the last five trials with goggles in the stim group ârespondersâ than the controls. The data suggests that SVS may be capable of improving short-term adaptation to a locomotion task done under sensory discordance in a group of responsive subjects.</p
Vestibular brain changes within 70 days of head down bed rest
HeadĂą downĂą tilt bed rest (HDBR) is frequently utilized as a spaceflight analog research environment to study the effects of axial body unloading and fluid shifts that are associated with spaceflight in the absence of gravitational modifications. HDBR has been shown to result in balance changes, presumably due to sensory reweighting and adaptation processes. Here, we examined whether HDBR results in changes in the neural correlates of vestibular processing. Thirteen men participated in a 70Ăą day HDBR intervention; we measured balance, functional mobility, and functional brain activity in response to vestibular stimulation at 7 time points before, during, and after HDBR. Vestibular stimulation was administered by means of skull taps, resulting in activation of the vestibular cortex and deactivation of the cerebellar, motor, and somatosensory cortices. Activation in the bilateral insular cortex, part of the vestibular network, gradually increased across the course of HDBR, suggesting an upregulation of vestibular inputs in response to the reduced somatosensory inputs experienced during bed rest. Furthermore, greater increase of activation in multiple frontal, parietal, and occipital regions in response to vestibular stimulation during HDBR was associated with greater decrements in balance and mobility from before to after HDBR, suggesting reduced neural efficiency. These findings shed light on neuroplastic changes occurring with conditions of altered sensory inputs, and reveal the potential for central vestibularĂą somatosensory convergence and reweighting with bed rest.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/144707/1/hbm24037_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/144707/2/hbm24037.pd