Who wouldn’t want to experience, even for a few seconds, what zero gravity feels like? The very force that anchors us to Earth is actually influential to our own biology—and that of all flora and fauna on the planet.
However, astronauts, as lucky as they may seem, are one of the skilled workers with more illnesses and conditions associated with their line of work. Floating in zero gravity messes with the human body in big ways, but experts just found a new change that might clear up why re-acclimating to Earth is so difficult for some space travellers.
The damage doesn’t happen in long-term missions; just spending a couple of weeks in orbit can physically reshape an astronaut’s brain in a way we can measure. If they end up staying up there for months (just like astronauts Sunita Williams and Butch Wilmore have had to endure for 9 months after initially embarking for an 8-day-long mission), those distortions can stick around for half a year or more.
Being in outer space might be cool, but many crew members end up having a hard time finding their footing again once they are once in gravity’s grasp.
A floating brain in gravity zero
A team headed by University of Florida physiologist Rachael Seidler states that they have clear evidence the brain shifts position inside the skull after space travel or similar simulations.
According to the researchers, these results are essential for figuring out how spaceflight impacts human behavior and brain function. When people go to space, their internal tissues tend to move around a good deal. With gravity out of the picture, the liquids in the body begin to spread out more evenly.
That isn’t necessarily a huge issue, but it does change the way the brain fits inside the cranium. Past studies have already pointed out that the brain’s center of mass floats higher up in the head after a trip to space than it did before launch.
The neural and cardiovascular consequences of staying in space too long
There are other signs that the situation inside the skull gets a bit weird. Back in 2015, a study looked at people stuck in tilted beds with their heads down—a technique used on Earth to simulate how fluids move in zero-g—and found that specific parts of the brain actually changed in size, rather than just shifting position.
Seidler and her team wanted to build on those clues to put hard numbers on what exactly happens to the brains of space travelers. The group examined 26 astronauts: 15 underwent brain scans before and after their missions specifically for this project, while the data for the other 11 came from existing records.
They also reviewed measurements from 24 people who participated in a two-month bed-rest experiment organized by the European Space Agency. The precise measurements showed that the brain slides up and back inside the cranium during space travel, while also tilting backward just a bit—a tiny rolling motion that matches what earlier studies saw.
However, the movement wasn’t uniform; different areas shifted in different directions, which means this isn’t simply a case of the entire brain moving as one unit. This indicates that the brain’s actual shape is being altered. For astronauts in orbit for a year, the changes were of two or three milimeters.
Balance and recovery once back on Earth
None of these structural adjustments appeared to impact the astronauts’ personalities, intelligence, or thinking skills. Instead, the most significant alterations occurred in the specific areas that manage how the brain tracks body position and movement.
The most dramatic changes occurred in the posterior insula, the specific brain area responsible for processing balance. The team found that the more this area shifted, the worse the astronaut’s balance was upon returning to Earth. Crew members frequently mention having trouble staying steady for days or even weeks after touchdown, while finer sensorimotor recovery can drag on for months.
What this entails for future long-distance space travels
If physical warping of the brain affects recovery, this insight could help scientists create better plans to help astronauts readjust to life on Earth.
The researchers note that this study—fully published in the Proceedings of the National Academy of Sciences—improves our grasp of how zero gravity alters brain anatomy, giving us solid numbers to aim for when creating treatments and recovery plans to keep future space explorers healthy.
They add that we need to look closer at how these brain shifts and distortions affect health and performance to ensure human space exploration becomes safer.