Long stays in orbit do more than test endurance and technology. New research suggests that spaceflight physically alters how the human brain sits inside the skull, with effects that can linger months after astronauts return to Earth.

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Scientists say the findings add to growing evidence that microgravity reshapes the human body in unexpected ways.

Brains on the move

A team led by Rachel Seidler at the Massachusetts Institute of Technology examined how extended exposure to microgravity affects the brain’s position.

The researchers studied 26 astronauts, along with 24 people drawn from other studies and participants in an Earth-based experiment designed to simulate weightlessness, reports WPTech.

Using MRI scans taken before and after space missions, the scientists detected measurable shifts in brain position. The brain moved both upward and backward inside the skull, affecting multiple regions rather than a single area.

The researchers described these changes as widespread and consistent among people who spent significant time in space.

Changes that last

According to the study, astronauts who spent between two weeks and a year aboard the International Space Station experienced brain shifts of up to 2.52 millimetres. Some of these changes were still visible as long as six months after they returned to Earth.

The persistence of the shifts suggests that the brain does not immediately return to its original alignment once gravity is restored.

The study found that the longer the exposure to microgravity, the more pronounced the changes tended to be.

Earth simulations compared

To better understand the role of gravity, scientists compared astronauts with participants who took part in a “bed rest” experiment on Earth, lying upside down to mimic some effects of weightlessness.

The results showed clear differences. Astronauts experienced a stronger upward shift of the brain, while bed-rest participants showed more backward movement.

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Only some of the space-related changes could be reproduced under Earth-based conditions, highlighting the limits of simulations.

Effects on movement

The authors noted that altered brain alignment may help explain balance and orientation problems astronauts often face after landing. These issues are linked to the inner ear and motor control.

While most astronauts regain normal balance within about a week, the anatomical brain changes last far longer.

Limits and next steps

The researchers cautioned that the study involved a relatively small number of participants and a limited observation period.

They are now planning further studies with larger astronaut groups to better understand why these shifts occur and how they affect recovery after spaceflight.