Researchers report that even short stays in microgravity produce measurable changes in brain shape and position, with the largest and longest-lasting effects appearing in regions tied to balance and sensorimotor control. The study analysed 26 astronauts and 24 volunteers in a 60-day head-down tilt analogue, finding upward and backward brain shifts and region-specific deformations. Year-long missions produced the biggest changes (about 2–3 mm), and larger displacements in the posterior insula were linked to worse balance after return. No evidence linked these structural shifts to declines in personality, intelligence, or general cognition.
Spaceflight Reshapes Astronaut Brains: Small Lasting Shifts Tied to Postflight Balance Problems
Astronauts Return to Earth With Lasting Brain Changes
Spending time in weightlessness doesn't only affect muscles and bones — new research shows it can subtly change the shape and position of the human brain. Scientists now report that missions as short as a few weeks produce measurable brain shifts, and longer missions can leave alterations detectable for at least six months.
What the study found
The team, led by physiologist Rachael Seidler of the University of Florida, analysed brain scans from 26 astronauts (15 newly scanned before and after flight and 11 from earlier reports) and compared these with scans from 24 volunteers who completed a 60-day head-down tilt bed-rest study run by the European Space Agency. Their fine-grained measurements revealed that during spaceflight the brain tends to shift upward and backward inside the skull and tilts slightly rearward. Different regions moved in different directions, indicating real deformation of brain shape — not just the whole brain sliding within the skull.
Shifts were small — generally a few millimetres — but larger effects were tied to longer missions. Astronauts who spent roughly a year in space showed deformations of about 2–3 mm in some regions. The bed-tilt analogue reinforced the role of fluid redistribution: the brain's ventricles (fluid-filled cavities) also shifted upward in both microgravity and the head-down tilt condition.
Functional links and safety implications
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The largest anatomical changes were concentrated in areas involved in balance and sensorimotor control, especially the posterior insula, a region that helps process vestibular and bodily-position signals. The study found that larger displacements in the posterior insula were associated with poorer balance performance after returning to Earth — a likely contributor to the days-to-weeks of instability many astronauts report after landing. Importantly, researchers did not find evidence that these structural changes were linked to alterations in personality, general intelligence, or broad cognitive ability.
Why this matters
Fluid redistribution in microgravity appears to be a key driver of these anatomical effects. Understanding the precise nature and time course of brain displacement and deformation gives mission planners quantitative targets for rehabilitation and countermeasures. As the authors note: "We demonstrate comprehensive brain position changes within the cranial compartment following spaceflight and an analog environment," and that the results are critical for protecting health and performance during future deep-space missions.
Published in Proceedings of the National Academy of Sciences, this work highlights a potentially reversible, measurable phenomenon with direct implications for postflight recovery programs.
Next steps
Researchers call for further study to determine how long deformations persist, whether repeated flights compound effects, and which interventions (preflight conditioning, inflight countermeasures, or focused postflight rehab) best restore Earth-adapted balance and sensorimotor function.
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