The brains of astronauts compress and expand in space, a study by a research team from the University of Michigan found. Using astronaut MRIs taken before and after previous NASA space missions, the researchers were able to show that the brains underwent stress.

Why this matters: The findings could have implications for future space travel, and for treating other health conditions that affect brain function.

The study, published in Nature Microgravity, is the first of its kind to look at structural changes to the human brain during spaceflight. It shows that the volume of gray matter increases or decreases slightly in space. The extent of those changes depends on the amount of time a human spends in space.

To be clear, the changes are slight and likely wouldn't affect an astronaut during travel to Mars or beyond. But they are changes in the human brain, so experts will need to determine what it means before humans spend considerable time in space.

Why does this happen? The short answer may be that the fluid in your brain shifts around while you're in space and not subject to the pull of gravity, causing the brain's size to increase or decrease slightly. Essentially, gray matter volume decreases slightly as fluid is redistributed. It later returns as gravity pulls that fluid down in the body.

Though they haven't pinpointed the exact nature of the changes, the findings may lead to new ways of thinking about potentially debilitating health condition — for instance, people on long-duration bed rest or people who have a condition where fluid accumulates in ventricles in the brain and causes pain and pressure.

What's next: Researchers are going to study possible repercussions on cognition and physical performance, as well as how long the brain changes last.

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