The hippocampus is a particularly plastic and vulnerable brain structure. Given the modulatory role of the vestibular system on hippocampal function, we hypothesized that altered vestibular stimulation associated with prolonged spaceflight could lead to similar hippocampal volume changes in astronauts after long-duration spaceflight and in individuals with bilateral vestibulopathy (BV), as a ground analog of spaceflight. We quantified hippocampal volumes using magnetic resonance imaging (MRI) in astronauts before and after spaceflight and in BV patients relative to matched healthy controls.
MRI analyses revealed a significant decrease in the left hippocampal volume (-2%) and an increase in the total volume of the ventricles (+11%) postflight in astronauts. The variations in volume of right and left hippocampus and ventricles were not correlated with each other, suggesting that the cerebrospinal fluid redistribution that occurs with spaceflight does not contribute to hippocampal volume changes. BV patients exhibited reduced hippocampal volumes compared to matched controls (-6% left and -4% right), suggesting that reduction of vestibular inputs, due either to microgravity or a disease, may contribute to hippocampal atrophy.
Furthermore, in both astronauts and BV patients, hippocampal volume correlated negatively with age, suggesting increased vulnerability of older individuals to vestibular-related neurodegeneration. Overall, our findings suggest that hippocampal atrophy in astronauts is not driven by mechanical compression, due to CSF redistribution but it may be affected by reduced vestibular input, aligning with observations in terrestrial vestibular loss. This work was supported by National Aeronautics and Space Administration grant # NNX11AR02G and Conseil Régional de Normandie grant # 00115524-210E06581.
The authors thank the members of the Association Française de Vestibulopathie Bilatérale who volunteered to participate in this study. These authors contributed equally: Olga Kuldavletova, Paola Kola. Department of Applied Physiology and Kinesiology, University of Florida, Gainesville, FL, USA Olga Kuldavletova, Tianyi Wang & Rachael D.
Seidler INSERM, COMETE, CHU Caen, Normandie Univ, Université de Caen Normandie, Caen, France Paola Kola, Thomas Caille, Gaëlle Quarck, Pierre Denise & Olivier Etard Normandie Univ, CNRS, INSERM, GIP Cyceron, UAR3408 US50, Université de Caen Normandie, Caen, France Center for Space Medicine and Extreme Environments Berlin, Institute of Physiology, University Medical Center Berlin, Berlin, Germany Neuroscience Laboratory, NASA Johnson Space Center, Houston, TX, USA The authors declare no competing interests. Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Open Access This article is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License, which permits any non-commercial use, sharing, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if you modified the licensed material.
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