Spaceflight takes a physical toll on astronauts, causing muscles to atrophy, bones to thin and bodily fluids to shift. According to a new study published in the journal PNAS, we can now add another major change to that list. Being in microgravity causes the brain to change shape.
Here on Earth, gravity helps to keep the brain anchored in place while the cerebrospinal fluid that surrounds it acts as a cushion. Scientists already knew that, without gravity’s steady pull, the brain moves upward, but this new research showed that it is also stretched and compressed in several areas.
Brains on the move
Researchers led by Rachel Seidler at the University of Florida reached this conclusion after studying MRI scans of 26 astronauts taken before and after their missions to the International Space Station. These were compared with scans from 24 volunteers who participated in a head-down tilt bed rest experiment. They spent 60 days lying at a six-degree downward angle to mimic how weightlessness causes bodily fluids and organs to move toward the head.
The study authors found significant differences between the brains of astronauts and those of the volunteers. While both groups experienced a shift, the astronauts’ brains moved further upward. And the longer they stayed in space, the more pronounced these changes became. The supplementary motor cortex (which helps to control movement) moved upward by about 2.5 millimeters in astronauts on one-year missions.
The brain movement isn’t uniform. The team discovered that as the brain moves, it becomes compressed at the top and the back while other areas stretch. This has a noticeable effect on balance and coordination. In tests, astronauts who experienced the largest brain shifts struggled the most to stay steady on their feet after returning to Earth.
Safer missions
For the future of space missions, it is vital to understand these changes, as the researchers note in their paper. “We demonstrate comprehensive brain position changes within the cranial compartment following spaceflight and an analog environment. These findings are critical for understanding the effects of spaceflight on the human brain and behavior.”
While the brain mostly returns to its normal position after several months back on Earth, scientists still need to know more to ensure safer conditions for longer missions, such as those to Mars.
“The health and human performance implications of these spaceflight-associated brain displacements and deformations require further study to pave the way for safer human space exploration.” https://phys.org/news/2026-01-spaceflight-astronauts-brains-shift-compress.html
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