Spending months in orbit doesn't just weaken astronauts' bones and muscles—it nudges their brains upward inside their skulls, a new study finds. In MRI scans of 26 astronauts taken before and after missions in microgravity, researchers saw the brain tilt and shift up and back, according to findings published in the Proceedings of the National Academy of Sciences. The regions most affected help process balance and motion, which may explain the disorientation, motion sickness, and balance problems many astronauts report during and after flights, per NBC News. "We need to understand these changes and their impacts to keep astronauts safe and healthy," said co-author Rachael Seidler of the University of Florida.
The shifts were "visible by eye" in astronauts who had stayed in space for at least six months, reaching "a couple of millimeters," Seidler said, and growing with mission length. Those who spent roughly a year on the International Space Station showed the biggest changes; even two-week shuttle fliers showed some movement, but duration appeared to be the main driver. Similar, though smaller, brain shifts showed up in 24 volunteers on Earth who spent up to 60 days on a tilted bed so that their heads were positioned below their feet, a common Earth-based stand-in for microgravity.
Despite the structural changes, the study did not find serious symptoms such as headaches or cognitive decline during or after missions, a result Seidler called unexpected. But many questions remain, including possible differences by sex and age and the long-term effects of repeated missions. Most changes appear to reverse after astronauts return to full gravity, yet it is unclear how brains will adapt to extended stays on the moon or Mars, where gravity is weaker. Researchers say that rather than arguing against human spaceflight, the findings highlight the medical puzzles that must be solved as space agencies push toward longer, deeper missions.
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