A new study has found that long stays in microgravity cause measurable shifts and deformations in the human brain, changes that in some cases persist months after astronauts return to Earth — findings with potential implications for future missions to the moon, Mars and beyond.
The research, published Jan. 12 in the journal Proceedings of the National Academy of Sciences, examined brain scans of astronauts before and after spaceflight and found that the brain moves upward and backward inside the skull during time in space. The extent of the shift increases with the length of the mission and affects sensory and motor regions linked to balance, orientation and movement.
What happens to the brain in space?
The study analyzed MRI data from 26 astronauts whose missions ranged from short shuttle flights to six-month stays aboard the International Space Station, with some astronauts spending close to a year in orbit. For comparison, researchers also examined brain scans from 24 participants in a long-duration bed rest experiment on Earth designed to simulate some effects of microgravity.
“When humans return from space, their average brain position is higher within the cranial compartment,” the authors wrote.
The research team, led by Tianyi Wang and Dr. Rachael Seidler of the University of Florida, found that the brain not only shifts upward and backward but also undergoes more complex, nonlinear deformations that were not captured in earlier studies. These changes varied between different regions of the brain and were sometimes symmetrical from left to right, meaning they were previously hidden when only average movement was measured.
Among astronauts who spent about a year in space, the largest upward displacement — about 2.5 millimeters — was observed in the supplementary motor cortex, a region involved in planning and coordinating movement.
The study also found a functional link between brain movement and physical performance. Larger shifts in a multisensory brain region known as the posterior insula were associated with greater declines in balance after astronauts returned to Earth. Researchers said this suggests the structural changes may contribute to the disorientation and balance problems often reported after spaceflight.
Although much of the brain’s movement reversed within six months of return to Earth, some changes persisted, particularly in astronauts who had spent the longest time in space.
“Understanding how spaceflight impacts the human brain is crucial as space exploration and tourism expand,” the authors wrote in the study’s significance statement, noting that the long-term health and performance effects of these changes are not yet fully understood.
Israeli space medicine physician Dr. Eran Shankar said the findings reinforce concerns that the effects of microgravity on the brain are not limited to temporary fluid shifts.
“It was already known that in microgravity, body fluids move toward the head,” Shankar said. “What this study shows is that the brain itself changes position and shape, and that these effects don’t disappear immediately after landing.”
According to Shankar, such changes could help explain symptoms including space motion sickness, dizziness, fatigue and balance problems, some of which can persist for months after astronauts return.
The researchers emphasized that the findings should not be viewed as a warning against long-term human spaceflight. Similar to bone loss and muscle weakening, the brain changes appear to be largely reversible. Still, they said more research is needed to determine whether different gravity environments — such as the moon, where gravity is about one-sixth of Earth’s, or Mars, where it is about one-third — could alter recovery time or long-term outcomes.
The authors said understanding these brain shifts will be essential for developing countermeasures to protect astronaut health as missions grow longer and human activity in space expands.