Visuomotor Adaptation Brain Changes During a Spaceflight Analog With Elevated Carbon Dioxide (CO2): A Pilot Study

Abstract

Astronauts on board the International Space Station (ISS) must adapt to several environmental challenges including microgravity, elevated carbon dioxide (CO2), and isolation while performing highly controlled movements with complex equipment. Head down tilt bed rest (HDBR) is an analog used to study spaceflight factors including body unloading and headward fluid shifts. We recently reported how HDBR with elevated CO2 (HDBR+CO2) affects visuomotor adaptation. Here we expand upon this work and examine the effects of HDBR+CO2 on brain activity during visuomotor adaptation. Eleven participants (34 ± 8 years) completed six functional MRI (fMRI) sessions pre-, during, and post-HDBR+CO2. During fMRI, participants completed a visuomotor adaptation task, divided into baseline, early, late and de-adaptation. Additionally, we compare brain activity between this NASA campaign (30-day HDBR+CO2) and a different campaign with a separate set of participants (60-day HDBR with normal atmospheric CO2 levels, n = 8; 34.25 ± 7.9 years) to characterize the specific effects of CO2. Participants were included by convenience. During early adaptation across the HDBR+CO2 intervention, participants showed decreasing activation in temporal and subcortical brain regions, followed by post- HDBR+CO2 recovery. During late adaptation, participants showed increasing activation in the right fusiform gyrus and right caudate nucleus during HDBR+CO2; this activation normalized to baseline levels after bed rest. There were no correlations between brain changes and adaptation performance changes from pre- to post HDBR+CO2. Also, there were no statistically significant differences between the HDBR+CO2 group and the HDBR controls, suggesting that changes in brain activity were due primarily to bed rest rather than elevated CO2. Five HDBR+CO2 participants presented with optic disc edema, a sign of Spaceflight Associated Neuro-ocular Syndrome (SANS). An exploratory analysis of HDBR+CO2 participants with and without signs of SANS revealed no group differences in brain activity during any phase of the adaptation task. Overall, these findings have implications for spaceflight missions and training, as ISS missions require individuals to adapt to altered sensory inputs over long periods in space. Further, this is the first study to verify the HDBR and elevated CO2 effects on the neural correlates of visuomotor adaptation.

Acute Gravitational Stress Selectively Impairs Dynamic Cerebrovascular Reactivity in the Anterior Circulation Independent of Changes to the Central Respiratory Chemoreflex

“…Importantly, these findings provide the possibility that CO 2 homeostasis in the brain may be altered via modified CO 2 regulatory mechanisms in space. Indeed, it has been reported that long-term microgravity decreased cognitive function (Salazar et al, 2020(Salazar et al, , 2021 and that this is associated with impaired CVR (Kim et al, 2021).…”

Head-Down-Tilt Bed Rest With Elevated CO2: Effects of a Pilot Spaceflight Analog on Neural Function and Performance During a Cognitive-Motor Dual Task

“…We processed the dual task data from the HDBR and HDBR + CO 2 subjects using identical procedures to our past work ( Hupfeld et al, 2020a ; Salazar et al, 2020 , 2021 ) using the established Statistical Parametric Mapping software (SPM12, version 7219) ( Ashburner et al, 2016 ) and pipeline ( Penny et al, 2011 ; Ashburner et al, 2016 ) through MATLAB R2016a (version 9.0). We first corrected functional images for slice timing and realigned the images to correct for volume-to-volume head motion.…”

“…Montreal Neurological Institute template-based normalization does not accurately warp the cerebellum ( Diedrichsen, 2006 ; Diedrichsen et al, 2009 ). Instead, identical to our past work ( Hupfeld et al, 2020a ; Salazar et al, 2020 , 2021 ), we implemented a combination of two optimized cerebellar processing pipelines, CEREbellum Segmentation (CERES) ( Romero et al, 2017 ) and the Spatially Unbiased Infratentorial Template (SUIT) ( Diedrichsen, 2006 ; Diedrichsen et al, 2009 ). We used CERES to extract and segment the cerebellum, according to a cerebellum-specific tissue type probability map and the T1-weighted image from each subject and session.…”

“…To characterize the differential effects of HDBR with and without elevated CO 2 , we calculated baseline (i.e., intercept) and slope of change statistical images for each subject of both the HDBR + CO 2 and HDBR studies. To calculate these images, we used the brain activation maps for sessions 2–4, in an identical manner to our previous HDBR and HDBR+CO 2 analyses ( Yuan et al, 2016 , 2018 ; Hupfeld et al, 2020a ; Salazar et al, 2020 , 2021 ). We calculated regression intercepts and slopes by using weights for each image.…”

Sensory system-specific associations between brain structure and balance

“…Similar to our past work (Hupfeld et al, 2021b;Salazar et al, 2020Salazar et al, , 2021, we applied specialized preprocessing steps to the cerebellum to produce cerebellar volume maps, with improved normalization of the cerebellum (Diedrichsen, 2006;Diedrichsen et al, 2009). We entered each participant's whole-brain T 1 -weighted image into the CEREbellum Segmentation (CERES) pipeline (Romero et al, 2017).…”