By David Kim, The Appleton Times
GAINESVILLE, Fla. — Astronauts returning from space missions experience subtle but significant shifts in their brain structure, with the organ tilting upward and repositioning within the skull, according to a new study that could influence NASA's ambitious plans for extended voyages to the moon and Mars.
The research, published Monday in the journal Proceedings of the National Academy of Sciences, examined MRI scans from 26 astronauts before and after their time in orbit. The participants had spent anywhere from a few weeks on space shuttle flights to about six months on the International Space Station, with a handful enduring yearlong missions. Researchers found that the brains of these astronauts shifted upward and backward relative to their Earth-bound positions, particularly affecting sensory regions associated with motion sickness, disorientation, and balance.
"The people who went for a year showed the largest changes," said Rachael Seidler, a professor in the department of applied physiology and kinesiology at the University of Florida and a co-author of the study. "There were still some changes evident in people who went for two weeks, but duration seems to be the driving factor."
Seidler noted that for astronauts on missions lasting six months or longer, the upward movement was especially pronounced in structures at the top of the brain. "It's on the order of a couple of millimeters," she explained, "which doesn't sound like a big number, but when you're talking about brain movement, it really is. That kind of change is visible by eye."
These alterations, while not linked to severe symptoms like headaches or cognitive impairment in the study, can lead to temporary challenges. In space, they sometimes cause "sensory conflicts" resulting in disorientation or motion sickness. Upon returning to Earth, the shifts contribute to balance issues as astronauts readjust to gravity. "That was surprising to me," Seidler said of the absence of more serious effects.
To contextualize the findings, the research team compared the astronauts' scans to those of 24 civilians on Earth who underwent simulated microgravity conditions. These participants were placed on bed rest for up to 60 days, tilted back so their heads were 6 degrees below their feet. Similar brain position and shape changes occurred, though the astronauts' brains showed greater upward shifts.
The study builds on a burgeoning field of aerospace medicine, which investigates how microgravity impacts the human body. Such effects are well-documented in areas like bone density loss and muscle weakening, but neurological changes have received less attention until recently. As NASA prepares for its Artemis program, which aims to establish a lunar base and eventually send humans to Mars, understanding these adaptations is essential.
"We need to understand these changes and their impacts to keep astronauts safe and healthy and protect their longevity," Seidler emphasized. The space agency's astronaut corps, historically male-dominated, launches only about a dozen individuals to the International Space Station annually, limiting sample sizes for such research.
Dr. Mark Rosenberg, an assistant professor of neurology at the Medical University of South Carolina and director of its aerospace and performance neurology program, who was not involved in the study, praised its contributions. Scientists have long known that spaceflight affects the brain, but linking those shifts to functional impacts is newer territory. "We knew the brain shifts upward, but does it actually have any kind of operational impact?" Rosenberg said. "This study is able to make some of those associations."
Rosenberg highlighted open questions raised by the research, including potential differences based on gender or age among astronauts. With NASA's corps skewing toward men, these variables remain underexplored. The study did not delve into long-term effects, but preliminary evidence suggests the changes are reversible. Like other space-induced bodily adjustments—such as fluid redistribution—brains appear to return to normal once acclimated to Earth's gravity.
However, the implications for partial gravity environments, like the moon's one-sixth or Mars's one-third of Earth's pull, introduce uncertainties. "If you've been on Mars with one-third Earth's gravity, or on the moon with one-sixth Earth's gravity, will it take three or six times as long to get back to normal?" Rosenberg wondered.
Neither Seidler nor Rosenberg views the findings as a deterrent to human space exploration. Instead, they underscore the need for further investigation to mitigate risks. "Whether we care to admit it or not, we are eventually going to become a space-faring species," Rosenberg said. "It's only a matter of time. And these are just some of the unanswered questions that we need to sort out."
The research arrives amid NASA's push toward deeper space travel. The Artemis I mission, an uncrewed test flight around the moon, launched successfully in November 2022, paving the way for crewed landings targeted for 2025 or later. Meanwhile, the International Space Station continues to host rotating crews, providing a vital laboratory for studies like this one.
Experts agree that while the brain shifts observed are measurable, they do not appear to cause permanent damage based on current data. Follow-up studies could track astronauts over years to confirm this, potentially incorporating larger, more diverse samples as NASA's programs diversify. For now, the work highlights the body's remarkable adaptability—and its vulnerabilities—in the void of space.
As humanity eyes the stars, from lunar outposts to Martian frontiers, safeguarding neurological health will be key to sustainable exploration. The University of Florida team's findings offer a foundational step, reminding us that even the most routine aspects of human physiology, like brain positioning, demand reevaluation in extraterrestrial settings.