For the first time, there have been accurate measures of volume changes in the brain tissues of long-term visitors to the International Space Station (ISS). An international group of neuroscientists, headed by Floris Wuyts at the University of Antwerp, quantified the changes after conducting MRI scans on Russian cosmonauts before, shortly after, and months after their journeys into space. Their results could help identify some previously-unknown risks of long-term spaceflight.
Astronauts who spend a long time aboard the ISS can have their bodies profoundly affected by microgravity. Most remarkably, their muscles and bones have a higher chance of atrophy once they come back to Earth as a result of microgravity. This leads space programmes to enforce strict exercise regimes on their astronauts.
However, the cognitive effects of long-term space travel are far less known. Without any significant measures to prevent damage to astronauts’ brains after they come back to Earth, it is presently unknown whether prolonged stays on the ISS could result in cognitive deterioration later in their lives.
Thus, to learn more about the risks involved, Wuyts’ team conducted MRI scans on the brains of 10 Russian cosmonauts, with an average space-mission duration of 189 days. For each person, the researchers conducted scans both before and shortly after their flight, in addition to a third scan several months later for seven of the candidates.
This method represents a major advance for neurological studies of astronauts. Peter zu Eulenburg, a co-author from the Ludwig Maximilian University of Munich, explained that this is the first study where it was possible to objectively quantify changes in brain structures after a space mission also including an extended follow-up period.
In particular, the team observed volume differences in each cosmonaut’s grey matter – made up of neuronal cell bodies, white matter – or nerve fibres, and cerebrospinal fluid (CSF) – which occupies the brain’s internal ventricles and the spaces between the brain and the skull.
Wuyts and his team discovered that, on average, the volume of the cosmonauts’ grey matter was reduced during their spaceflights, then partially came back after seven months – but not completely. In comparison, their white matter volumes were unchanged while in space but were significantly lowered after six months back on Earth.
Moreover, CSF volumes increased aboard the ISS, then continued to expand in the spaces outside the brain once the astronauts were back on Earth; but volumes returned almost back to normal inside the ventricles.
The neuroscientists suggest that the post-flight reduction in white matter that they witnessed could be explained by the combined recovery of grey matter and continued expansion of CSF lessening the space available for white matter. If this is true, the team’s findings suggest that the long-term changes to the brain after spaceflight could be far more unpredictable than presently thought.
zu Eulenburg explained that their results highlight prolonged changes in the pattern of cerebrospinal fluid circulation for at least seven months after the return to Earth. He added that whether or not the extensive alterations are shown in the grey and the white matter lead to any changes in cognition is still unclear so far.
As of now, the only known clinical condition affecting long-term ISS visitors long after they come back to Earth is reduced eyesight – an effect Wuyts’ team now think could be the result of an increased pressure exerted by expanded CSF on the retina. But, the researchers suspect that other, not-yet observed and potentially dangerous cognitive conditions could manifest long after an astronaut comes home.
Wuyts and colleagues also believe a wider range of diagnostic methods will be vital for identifying and lowering the risks of prolonged space travel.