Abstract
Humans undergo extreme physiological changes when subjected to long periods of weightlessness, and as we continue to become a space-faring species, it is imperative that we fully understand the physiological changes that occur in the human body, including the brain. In this study, we present findings of brain structural changes associated with long-duration spaceflight based on diffusion magnetic resonance imaging (dMRI) data. Twelve cosmonauts who spent an average of six months aboard the International Space Station (ISS) were scanned in an MRI scanner pre-flight, ten days after flight, and at a follow-up time point seven months after flight. We performed differential tractography, a technique that confines white matter fiber tracking to voxels showing microstructural changes. We found significant microstructural changes in several large white matter tracts, such as the corpus callosum, arcuate fasciculus, corticospinal, corticostriatal, and cerebellar tracts. This is the first paper to use fiber tractography to investigate which specific tracts exhibit structural changes after long-duration spaceflight and may direct future research to investigate brain functional and behavioral changes associated with these white matter pathways.
Highlights
The human brain retains a high degree of neuroplasticity into adulthood
For decreasing quantitative anisotropy (QA) there were changes located in the Corpus Callosum Forceps Major, Left Thalamic Radiation Posterior, Corpus Callosum Tapetum, Corpus Callosum Body, Left Corticostriatal Tract Posterior, Right Inferior Longitudinal Fasciculus, Right Thalamic Radiation Posterior, Right Cingulum Parahippocampal Parietal, Right Corticostriatal Tract Posterior showing decreased QA (FDR = 0.0014) (Figure 3 and Table 2)
Our findings demonstrate widespread microstructural changes associated with long-duration space flight within the sensorimotor tracts including many tracts connecting the cerebellum, as well as within the corpus callosum, inferior fronto occipital fasciculus (IFOF) and arcuate fasciculus
Summary
The human brain retains a high degree of neuroplasticity into adulthood. Dependent neuroplastic responses are maintained through the same mechanisms that allow for profound developmental and learning-dependent changes (Pascual-Leone et al, 2005). The adult brain may be subject to mechanical forces that exert mass effects—changing the shape and microstructural organization of the brain (Laitinen et al, 2015). Spaceflight has the potential to profoundly alter both the function and shape of the adult brain. While the physiological effects of spaceflight have been studied for many decades, research into the effects of spaceflight on the brain is still in its infancy. The human desire to increase our exploration of space exacerbates the need to understand the effects of spaceflight on the human brain
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