Swollen chambers in astronauts’ brains may take 3 years to recover

The chambers collect extra fluid in the microgravity of space

A photo of a woman putting a spacesuit helmet on astronaut Akihiko Hoshide.

Japanese astronaut Akihiko Hoshide suits up for a photo shoot ahead of his 2021 launch to the International Space Station. That mission lasted around six months. That’s about how long it takes for fluid-filled chambers in the brain to adapt to the microgravity of space.

Norah Moran/NASA

Spacing out spaceflights may be better for astronauts’ brains.

Fluid-filled chambers in the human brain expand while in space. It’s one way they adapt to lower gravity. But after a space mission, these structures don’t shrink back right away. It might take three years to return to normal. Researchers reported this June 8 in Scientific Reports.

This suggests astronauts might need at least that long between flights before their brain is ready to be in space again.

With little gravity in space, fluids build up in an astronaut’s head. Sometimes their faces even look puffy when space travelers first arrive at the International Space Station, says Rachael Seidler. She studies how the human body adapts to space. She works at the University of Florida in Gainesville.

Extra fluid also collects in four chambers in the brain, called ventricles. Astronauts often return to Earth with enlarged ventricles. These chambers are filled with liquid that cushions the brain and clears out cellular wastes. In space, the ventricles expand as they take in more fluid, Seidler says.

She and her colleagues wanted to see how time spent in space affected the brain.

They examined MRI scans of the brains of 30 astronauts. Ones taken before each astronaut’s missions were compared to those taken after time in space. The longer the mission, the more that three of the four ventricles seemed to expand. (The fourth ventricle is very small, Seidler notes. So any changes in it may have been too tiny to see.)

Two-week spaceflights didn’t have much effect. Both six- and 12-month missions, though, resulted in larger ventricles. The amount was similar after these longer trips, suggesting the swelling slows after six months in space.

Eighteen of the astronauts had flown in space before. The time since their last mission seemed to affect how much their brains changed during the new mission that the researchers were studying. In those whose last trip to space was three or more years earlier, three of their ventricles got bigger — on average, by roughly 10 to 25 percent. Other astronauts had been to space less than three years prior. Their ventricles didn’t swell much if at all. That suggests their brains may not have had enough time between missions to fully recover, the scientists say. 

“I’m glad that the [study] authors took the first step and are looking at this question,” says Donna Roberts. She’s a brain-imaging specialist at Medical University of South Carolina in Charleston. “There are so many variables that could play into the brain changes that we’re seeing,” Roberts says. “It’s hard to sort them out.”

Spaceflight’s effects on the brain are even more pressing now, she notes. NASA aims to send people to Mars, which could be a two-year round trip. “Everybody talks about the rocket technology to get to Mars,” Roberts says. But “the humans — that’s the real challenge.”

McKenzie Prillaman is the Spring 2023 science writing intern at Science News. She holds a bachelor’s degree in neuroscience with a minor in bioethics from the University of Virginia and a master’s degree in science communication from the University of California, Santa Cruz.

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