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

• Published in: Scientific reports Vol. 7; no. 1; pp. 3154 - 12
• Main Authors: Koppelmans, Vincent, Pasternak, Ofer, Bloomberg, Jacob J., Dios, Yiri E. De, Wood, Scott J., Riascos, Roy, Reuter-Lorenz, Patricia A., Kofman, Igor S., Mulavara, Ajitkumar P., Seidler, Rachael D.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 09.06.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 59; 59/57; 631/378/2632/1663; 692/698/1688/64; Adaptation; Adaptation, Physiological; Adult; Astronauts; Balance; Brain Mapping; Cortex (parietal); Diffusion Magnetic Resonance Imaging; Extracellular Fluid - physiology; Frontal Lobe - anatomy & histology; Frontal Lobe - diagnostic imaging; Frontal Lobe - physiology; Functional plasticity; Gait; Head-Down Tilt - physiology; Humanities and Social Sciences; Humans; Immobilization; Investigations; Longitudinal studies; Male; Medical imaging; Microgravity; Middle Aged; multidisciplinary; Neuroimaging; Neuronal Plasticity; Neuroplasticity; Parietal Lobe - anatomy & histology; Parietal Lobe - diagnostic imaging; Parietal Lobe - physiology; Postural Balance - physiology; Science; Science (multidisciplinary); Sensorimotor system; Space Flight; Substantia alba; Substantia grisea; Temporal Lobe - anatomy & histology; Temporal Lobe - diagnostic imaging; Temporal Lobe - physiology; Unloading; Water - physiology; Weightlessness Simulation - methods; White Matter - anatomy & histology; White Matter - diagnostic imaging; White Matter - physiology
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-017-03311-w

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.