At a Glance
- Astronaut brains shift upward and tilt back in the skull after spaceflight
- Changes are largest after year-long missions, still visible after two weeks
- Sensory-linked areas linked to motion sickness and disorientation affected
- Why it matters: Findings shape safety plans for NASA’s moon base and Mars trips
Spaceflight physically moves the brain inside the skull, new MRI data show, raising safety questions for NASA’s push toward months-long lunar and Martian missions.
The study, published Monday in Proceedings of the National Academy of Sciences, compared scans from 26 astronauts before and after their missions. Time aloft ranged from shuttle flights of a few weeks to standard six-month International Space Station tours; a handful stayed nearly a full year.
Brain Movement Detected
Researchers found the brain shifted up and back, with the topmost structures rising a couple of millimeters.
- 2 mm may sound tiny, but it is visible to the naked eye on a scan
- Duration drives the effect: longer missions produce larger shifts
- People who spent a year in orbit showed the greatest displacement
“The people who went for a year showed the largest changes,” said Rachael Seidler, University of Florida professor and co-author. “There were still some changes evident in people who went for two weeks, but duration seems to be the driving factor.”
What Changes Inside the Skull
The upward tilt affects regions tied to balance and spatial orientation.
Affected areas:
- Parietal and frontal lobes that integrate sensory input
- Structures linked to motion sickness and disorientation
- Tissue near the top of the cranial cavity
These shifts can create “sensory conflicts,” leading to temporary motion sickness in orbit and balance problems once crews return to Earth. The study recorded no headaches or cognitive decline, a result Seidler called surprising.
Earth-Based Comparison
To separate space-specific effects from simple head-down tilt, scientists placed 24 civilians on bed rest for 60 days with their heads 6° below their feet, mimicking fluid shifts caused by microgravity. Similar brain repositioning appeared, but astronauts still showed a greater upward slide.
Implications for Deep-Space Travel
NASA’s Artemis program envisions a sustained lunar base and eventual human trips to Mars. Understanding how living in fractional gravity alters the brain will shape countermeasures and habitat design.
Dr. Mark Rosenberg, Medical University of South Carolina neurologist, said the work operationalizes prior observations. “We knew the brain shifts upward, but does it actually have any kind of operational impact? This study is able to make some of those associations.”
Open questions include:
- Whether male and female astronauts differ in response
- Whether age changes vulnerability
- How long recovery takes on Mars (⅓ Earth gravity) or the moon (⅙ Earth gravity)
Sample-size limits slow answers; only about a dozen astronauts launch each year and most have been men.
Recovery and Outlook
Like bone loss and muscle atrophy, the brain shifts appear reversible once gravity resumes. Scans show structures drifting back toward pre-flight positions over time, though timelines for partial-gravity worlds remain unknown.
“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 asked.
Both researchers say the findings should not deter exploration, but they underscore the need for monitoring and mitigation as humanity becomes, in Rosenberg’s words, “a space-faring species.”
Key Takeaways
- MRI scans reveal measurable upward brain displacement after space missions
- Longer flights produce larger, more persistent changes
- No major cognitive symptoms detected so far
- Data will guide health safeguards for future moon and Mars crews
