Plastic floating in the skull
We all know the story: up there, without gravity, muscles waste away, bones become fragile, and blood rushes to the head. But now imagine what happens inside your skull. This is the fascinating finding made by researchers at MIT and NASA: in weightlessness, your brain does not stay put. It moves, and not just a little.
In a study published in the journal PNAS in January 2026, scientists examined the MRIs of 26 astronauts, some of whom had spent up to a year in orbit. The verdict? The brain does not act like a rigid block, but like a plastic material. Freed from gravity, it recedes, rises, and pivots slightly backward. To be precise, the researchers divided the brain into 130 distinct regions to track these movements. The result: the upper areas, particularly the motor cortex, move up to 2.5 millimeters in those who stay in space for a long time. More worryingly, the deeper regions undergo lateral displacement, creating a kind of internal shearing. Basically, the brain reconfigures itself because the skull was never designed for the vacuum of space.
Why astronauts lose their balance when they return
To measure this, the scientists used the SOT-5M test. The principle is simple: the subject is asked to move their head back and forth, with their eyes closed, on a moving platform. The astronauts whose brains had changed the most—particularly in the posterior insula—were also the ones who had the most difficulty standing up. According to Space.com, these balance problems can ruin the lives of returnees for a good week. But while the dizziness passes, the traces in the brain are more persistent.
After-effects visible six months later
This is where the study becomes truly compelling for the future of space exploration. MRIs performed six months after the astronauts’ return show that not everything has returned to normal. While some areas have returned to their original state, others have not. Recovery is partial and uneven. This proves that adaptation to microgravity is not just a temporary phenomenon, but a profound remodeling that could affect other functions, such as the elimination of brain waste via drainage. The researchers attempted to compare these results with 24 volunteers who remained bedridden on Earth with their heads tilted (the standard protocol for simulating weightlessness). Surprise: it doesn’t really work. On Earth, the brain mainly recedes, whereas in space, it actually rises. Furthermore, attempts at countermeasures, such as creating artificial gravity on a daily basis, did not change the deformations observed. As we set our sights on the Moon and Mars for much longer journeys, understanding how to protect our most precious organ is becoming an absolute priority. The human body is resilient, of course, but space seems determined to push it to its limits. According to the source: science-et-vie.com Created by humans, assisted by AI.