How the lack of gravity in space impacts astronauts' brains

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What happens to the brain when you take gravity away? According to a new study looking at astronauts both before and after space travel, that experience causes physical changes that researchers believe requires at least three years between longer missions to recover from.

The study looked at the brains of 30 astronauts and found that cavities within the brain had expanded during their time away from Earth.

Astronauts who went up into space for six months had the clearest change in their brains, while shorter trips of two weeks or less came with very little physical change in comparison.

“We found that the more time people spent in space, the larger their ventricles became,” Rachael Seidler, a professor of applied physiology and kinesiology at the University of Florida and an author of the study, said in a press release. “Many astronauts travel to space more than one time, and our study shows it takes about three years between flights for the ventricles to fully recover.”

It’s not actually a new idea that space travel changes our bodies. It’s long been documented that the lack of gravity affects the muscles and bone mass, and previous studies have also looked at how space impacts the brain’s morphology.

What happens when you spend time in space is that the lack of gravity allows the brain to essentially float up to the top of the skull, a physical shift seen in displacements of cerebrospinal fluid, which surrounds the brain. Previous research has tracked how astronauts returning home to Earth have then experienced decreases in the fluid at the top of the brain and increases in the volume at the base of the brain — fluid draining back down as gravity reasserts itself.

Within the brain itself, structures shift too. Gray matter, which is the tissue in the brain containing neurons and connections which enable much of our daily functioning, increases in volume at the top of the brain due to space travel, while decreasing in the base of the brain.

But while this phenomenon has been studied before, scientists still don’t know what the implications are for more long-term space travel.

HOW THE BRAIN CHANGES THE LONGER YOU SPEND TIME IN SPACE

What this new study, published Thursday in the peer-reviewed journal Scientific Reports, wanted to investigate was whether the impact on your brain grows more significant the longer you spend in space.

They found that the answer was yes — but that this effect didn’t start right away, or continue in perpetuity. Instead, there was a window of time in which the most changes took place.

“The biggest jump comes when you go from two weeks to six months in space,” Seidler said. “There is no measurable change in the ventricles’ volume after only two weeks.”

Ventricles are cavities in the blood that contain cerebrospinal fluid, a substance which helps to cushion the brain and spinal fluid and to deliver waste products from the brain. As the fluid is shifted upwards in the body due to the lack of gravity, it expands the ventricles in the brain.

Expanding ventricles is something that happens naturally as we age, but the expansion seen in the astronauts was larger than what happens during aging.

Researchers looked at both ventricle expansion and gray matter volume over time, and found that short space travel trips of two weeks or under either resulted in smaller ventricle increases, or even decreases, compared to longer trips.

Longer trips meant more ventricle enlargement and gray matter displacement, but at six months, this effect slowed down — a good sign, researchers say, that this effect won’t get exponentially worse as space trips get longer and longer.

“Crewmembers who completed 6-month and 1-year-long missions showed a similar degree of expansion of these ventricles following flight, providing preliminary evidence that changes begin to taper off during 6-month-long missions,” authors wrote in the study.

Half of the data was taken from an earlier study on the effects of spaceflight conducted between 2014 and 2020, which utilized astronauts who had spent either six months or a full year on the International Space Station. The other 15 astronauts came from the NASA Lifetime Surveillance of Astronaut Health Repository.

WHAT DOES THIS MEAN FOR ASTRONAUT RECOVERY?

If the brain is affected so much by one trip to space, what about multiple ones?

Researchers looked at the duration of time that astronauts had between spaceflights in order to see if this impacted their brain changes on their next trip.

They found that when astronauts had less than three years of time to recover after their previous space mission before heading up to space again, their ventricles expanded less on the second trip — because they hadn’t fully healed and returned to their normal state.

Scientists theorize that the expansion of the ventricles in the brain during spaceflight might help humans compensate for other impacts on the brain, meaning that a weakened ability to expand and contract could be an issue down the line.

If the ventricles are already enlarged from a previous long-term space trip when an astronaut returns to space, they may not be able to expand properly and will have less storage space for cerebrospinal fluid, meaning less protection for the brain.

Researchers say this study could help establish baselines for trip durations and recovery times for astronauts and space travellers as space tourism picks up and human beings increasingly reach out into the stars.

“We don’t yet know for sure what the long-term consequences of this is on the health and behavioural health of space travelers,” Seidler said, “so allowing the brain time to recover seems like a good idea.”

Only a handful of the astronauts included in the study had been on a year-long mission, meaning there’s still a lot of questions left regarding long-term space travel.

The study has a few other limitations, one of them being the lack of MRI scans for all participants, as well as differing MRI scan parameters between the two groups. Researchers obtained MRI brain scans of 28 of the astronauts, but only had full scans for 15 of them in total. The post-space-travel MRI scans were also obtained around six days on average after astronauts had landed back on Earth, meaning the brain may have already begun recovering from the space effects before the scan.