Prolonged microgravity induces reversible and persistent changes on human cerebral connectivity

Abstract

The prospect of continued manned space missions warrants an in-depth understanding of how prolonged microgravity affects the human brain. Functional magnetic resonance imaging (fMRI) can pinpoint changes reflecting adaptive neuroplasticity across time. We acquired resting-state fMRI data of cosmonauts before, shortly after, and eight months after spaceflight as a follow-up to assess global connectivity changes over time. Our results show persisting connectivity decreases in posterior cingulate cortex and thalamus and persisting increases in the right angular gyrus. Connectivity in the bilateral insular cortex decreased after spaceflight, which reversed at follow-up. No significant connectivity changes across eight months were found in a matched control group. Overall, we show that altered gravitational environments influence functional connectivity longitudinally in multimodal brain hubs, reflecting adaptations to unfamiliar and conflicting sensory input in microgravity. These results provide insights into brain functional modifications occurring during spaceflight, and their further development when back on Earth.

Influence of microgravity on spontaneous calcium activity of primary hippocampal neurons grown in microfluidic chips

“…There have been relatively few studies on the effects of weightlessness on the brain, and yet, decades of observations on space-flown animal models and human astronauts have confirmed that physiology is profoundly impacted by spaceflight 32 – 34 . Growing evidences show that prolonged exposure to spaceflight and microgravity environment leads to alteration of brain function and structure, as suggested by recent analyses of astronauts’ brain fMRI 10 . Even at a smaller scale, microgravity is known to have a direct effect on cells, such as the modification of their cytoskeleton or changes in their physical properties 3 , 35 .…”

“…In the same manner that microgravity modifies blood pressure, it also causes vestibular and ocular structural dysfunction as the fluid shift increases the intracranial and intraocular pressure leading to SANS (Spaceflight-Associated Neuro-ocular Syndrome) 8 , 9 . Extensive studies of astronauts alterations of brain structure has recently been substantiated by fMRI analysis of astronauts evidencing subtle yet significant modification of brain connectome 10 . These phenomena are either linked to microgravity itself, via mechanical unloading, or to the intracranial fluid redistribution, or to space radiation.…”

Influence of Microgravity on Spontaneous Calcium Activity of Primary Hippocampal Neurons.

“…There have been relatively few studies on the effects of weightlessness on the brain, and yet decades of observations on space-flown animal models and human astronauts have confirmed that physiology is profoundly impacted by spaceflight [17][18][19]. Growing evidences show that prolonged exposure to spaceflight and microgravity environment leads to alteration of brain function and structure, as suggested by recent analyses of astronauts' brain fMRI [5]. Even at a smaller scale, microgravity is known to have a direct effect on cells, such as themodification of their cytoskeleton or changes in their physical properties [20,21].…”

“…From a neurological point of view, medical studies on astronauts also showed that space flights have effects on the brain both on the short term (motion sickness, vestibular dysfunction and Spaceflight-associated neuroocular SANS syndrome) and on the long term (increased risk of brain malignancies, premature ageing, accelerated neurodegeneration) [3,4]. Alteration of brain structure has recently been substantiated by fMRI analysis of astronauts evidencing subtle yet significant modification of brain connectome [5]. These phenomena are either linked to microgravity itself, via mechanical unloading, or to the intracranial fluid redistribution, or to space radiation.…”

Physical exercise restores adult neurogenesis deficits induced by simulated microgravity

“…During spaceflights, astronauts report mental fatigue, disruptions of neurovestibular system, sleep and circadian rhythms, and difficulty concentrating and maintaining a high level of cognitive performance (Arshad and Ferré, 2023; Gupta et al, 2023; Mhatre et al, 2022; Oluwafemi et al, 2021). MRI investigations have revealed that the brain of astronauts undergoes a variety of changes as a consequence of spaceflight missions including changes in tissue volume and microstructure, cerebrospinal fluid distribution and dynamics, and functional connectivity (Gupta et al, 2023; Jillings et al, 2023; Roy-O’Reilly et al, 2021). Understanding how long-term exposure to reduced-gravity environments may influence the neuro-physiological processes and neuroplasticity, i.e.…”