The Brain in Space: Investigating the Effects of Long Spaceflights on Space Travellers

Roscosmos/ Vkontakte

As part of an international project conducted with the participation of Roscosmos and the European Space Agency, a team of researchers used differential tractography to analyse dMRI scans of cosmonauts’ brains and found significant changes in brain connectivity, with some of the changes persisting after seven months back on Earth. The paper is published in Frontiers in Neural Circuits.

Long-duration orbital flights are a serious test for the human body. The absence of Earth's gravity (a.k.a. microgravity) affects space travellers’ muscle contraction, vestibular system, vision and other senses. There is limited knowledge, however, on the effect of microgravity on the human brain. With space exploration progressing rapidly and missions to Mars becoming a not-so-distant reality, space travellers may soon be spending even more time—perhaps years—in space. Scientists have been working to gain a better understanding of the impact of microgravity on the human body to find ways to keep space travellers healthy and fit during long flights.

In a recent study, researchers from Russia, Belgium, Germany, the US, and Australia analysed changes in white matter pathways (tracts) in cosmonauts’ brains. White matter (WM) consists of bundles of nerve fibres connecting areas of grey matter (GM) which is made up of neuronal cell bodies. GM processes information, while the WM is the ‘wiring’ that enables communication between different parts of the brain and between the brain and the body.

The participants of the study underwent diffusion magnetic resonance imaging (dMRI) to observe changes in their WM tracts, and the data was then analysed using differential tractography. The dMRI method has only recently been applied to space travellers, and this study was the first to apply differential tractography to their dMRI scans. This method is unique because it makes it possible to produce accurate 3D images of the tracts and examine them on the microstructural level. In addition, dMRI is sensitive to free-water changes in WM. This finding is important, as earlier studies have demonstrated fluid redistribution in the skull in a microgravity environment.  

To observe brain changes over time, the participants—twelve Russian cosmonauts who spent an average of 172 days aboard the International Space Station (ISS)—underwent dMRI before the flight, with follow-up scans ten days and seven months after returning to Earth.

The researchers found changes in multiple WM tracts associated with motor and sensory functions such as vision and speech. While prior research has reported certain changes, eg in cortical motor areas, this study is the first to demonstrate that changes also occur at the level of deep-brain WM tracts.

The brain's ability to change and rewire its connections in response to experience is called neuroplasticity. It helps humans adapt, at least partly, to extreme environments. However, no reliable data is available on how such adaptive changes may affect human health and cognitive abilities.

Yet according to the study’ authors, not all changes in the brain can be attributed to neuroplasticity. Some may be due to anatomical shape alterations of the brain and fluid redistribution in the skull caused by microgravity. For example, changes in the corpus callosum (a WM tract that connects the cerebral hemispheres) can be caused by pressure from the adjacent ventricles–cerebrospinal fluid-filled cavities that expand during spaceflight.

Interestingly, some of the spaceflight-induced changes in the brain were still visible on dMRI scans performed during the seven-month postflight follow-up.

Ekaterina Pechenkova, study co-author and leading research fellow at the HSE University Laboratory for Cognitive Research

'Our study is an important step towards a better understanding of the effects of spaceflight on the brain. We still have a lot to learn, specifically: which of the observed phenomena are due to neuroplasticity and which can be attributed to CSF redistribution and related anatomical changes in the brain during spaceflight; why some changes disappear quickly while others persist; and finally, what these changes have to do with successful adaptation to a spaceflight environment. These are promising areas for further research.'

This research can offer insights into what kinds of training and conditioning can help space travellers maintain their brain fitness alongside exercises and equipment designed to keep their muscles and bones strong.