Scientists document how space travel messes with the human brain
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[June 09, 2023]
By Will Dunham
WASHINGTON (Reuters) - Space can be an unfriendly place for the human
body, with microgravity conditions and other factors tampering with our
physiology, from head to toe - head, of course, being a primary concern.
A new NASA-funded study provides a deeper understanding of the issue.
Researchers said on Thursday that astronauts who traveled on the
International Space Station (ISS) or NASA space shuttles on missions
lasting at least six months experienced significant expansion of the
cerebral ventricles - spaces in the middle of the brain containing
cerebrospinal fluid.
This colorless and watery fluid flows in and around the brain and spinal
cord. It cushions the brain to help protect against sudden impact and
removes waste products.
Based on brain scans of 30 astronauts, the researchers found that it
took three years for the ventricles to fully recover after such
journeys, suggesting that an interval of at least that duration would be
advisable between longer space missions.
"If the ventricles don't have sufficient time to recover between
back-to-back missions, this may impact the brain's ability to cope with
fluid shifts in microgravity. For example, if the ventricles are already
enlarged from a previous mission, they may be less compliant and/or have
less space to expand and accommodate fluid shifts during the next
mission," said University of Florida neuroscientist Heather McGregor,
lead author of the study published in the journal Scientific Reports.
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Age-related ventricular enlargement - caused not by microgravity but by
brain atrophy - can be associated with cognitive decline.
"The impact of ventricular expansion in space travelers is not currently
known. More long-term health follow-up is needed. This ventricular
expansion likely compresses the surrounding brain tissue," University of
Florida applied physiology and kinesiology professor and study senior
author Rachael Seidler said.
The absence of Earth's gravity modifies the brain.
"This seems to be a mechanical effect," Seidler said. "On Earth, our
vascular systems have valves that prevent all of our fluids from pooling
at our feet due to gravity. In microgravity, the opposite occurs -
fluids shift toward the head. This headward fluid shift likely results
in ventricular expansion, and the brain sits higher within the skull."
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Hurricane Genevieve is seen from the
International Space Station (ISS) orbiting Earth in an image taken
by NASA astronaut Christopher J. Cassidy August 19, 2020.
NASA/Christopher J. Cassidy/Handout via REUTERS/File Photo
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The study involved 23 male and seven female astronauts - average age
around 47 - from the U.S., Canadian and European space agencies.
Eight traveled on space shuttle missions of about two weeks.
Eighteen were on ISS missions of about six months and four on ISS
missions of about a year.
Little to no ventricular volume change occurred in astronauts after
short missions. Enlargement occurred in astronauts after missions of
six months or longer, though there was no difference in those who
flew for six months compared to those who did so for a year.
"This suggests that the majority of ventricle enlargement happens
during the first six months in space, then begins to taper off
around the one-year mark," McGregor said.
The fact that enlargement did not worsen after six months could be
good news for future Mars missions on which astronauts may spend two
years in microgravity during the journey.
"This preliminary finding is promising for astronaut brain health
during long-duration missions, but it's still important that we
examine MRI data from a larger group of astronauts and following
even longer missions," McGregor said.
The absence of enlargement following short flights was good news for
people who may consider short space tourism jaunts, Seidler added,
as that industry develops.
Microgravity conditions also cause other physiological effects due
to the reduced physical load on the human body. These include bone
and muscle atrophy, cardiovascular changes, issues with the balance
system in the inner ear and a syndrome involving the eyes. Elevated
cancer risk from the greater exposure to solar radiation that
astronauts may encounter the further they travel from Earth is
another concern.
(Reporting by Will Dunham, Editing by Rosalba O'Brien)
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