Cosmonaut brains show space travel causes lasting changes

A new study of Russian space travelers adds to evidence that life among the stars has many consequences.

Russian cosmonaut Alexander Skvortsov works on the International Space Station during a five-hour, 11-minute spacewalk.

Our fleshy forms evolved to work within the tug of gravity. Take that pull away, and the clockwork operation of bodily functions just doesn't keep ticking at the same steady beat. From fluids floating the wrong way to DNA expressing differently, space travel is tough on even the healthiest human body.

Now, a study of recently active cosmonauts adds to the concern for one particularly vital organ: the brain. The results suggest that deformations to brain tissue caused by weightless conditions can linger even after space travelers have had their boots back on Earth for seven months.

The research, published this week in the New England Journal of Medicine, documents the impacts of space travel on cosmonauts who each spent roughly 189 days on the International Space Station. Led by scientists at the University of Antwerp, the team captured images of 10 male cosmonauts' brains using magnetic resonance imaging before and after each mission. They repeated the scans seven months later for seven of these space adventurers.

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The blackness of space and Earth's horizon provide the backdrop for this image of the docked Soyuz 13 (foreground) and the Progress 22 resupply vehicle. Astronauts photographed the Soyuz from a window on the International Space Station while space shuttle Discovery was docked with the station.
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Astronaut Robert Curbeam works on the port overheard solar array wing on the International Space Station's P6 truss. Construction and repairs are an ongoing process on the ISS, which may be completed by 2010. When it's finished, the space station will be larger than a typical five-bedroom house.
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Discovery mission specialists Robert Curbeam (left) and Christer Fuglesang work on ISS construction during a spacewalk in 2006. Visiting astronauts typically live and work at the station for about six months before heading home.
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This view of the International Space Station over a blue-and-white Earth was taken shortly after the space shuttle Atlantis undocked from the orbital outpost on September 17, 2006. During its six days on the space station, the Atlantis crew installed a pair of 240-foot (73-meter) solar wings, attached to a 17.5-ton section of truss with batteries, electronics, and a giant rotating joint. The new solar arrays were designed to double the station's onboard power.
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A crew member aboard the space shuttle Endeavour snapped this image of the Pirs docking compartment of the International Space Station. The compartment has two primary functions: It serves as a docking port for transport and cargo vehicles and as an airlock for spacewalking astronauts.
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The turquoise waters of Miami, Florida, gleam underneath the International Space Station as it floats some 240 miles (390 kilometers) above the Earth's surface. The orbiting lab has hosted a rotating international crew since November 2000.
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The International Space Station has been under construction since November 1998. In that year the first piece of its structure, the Zarya Control Module, was launched into orbit with a Russian Proton rocket. Today the station features more space than the average three-bedroom house—and it's still growing.
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When renovations or repairs are needed on the International Space Station, it's up to astronauts to do the job. Before donning a special pressurized suit and heading out on a spacewalk, though, they must first spend over two hours decompressing in order to avoid the bends. Once their spacesuits are on, the astronauts must spend another hour breathing pure oxygen before they can step outside.
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As previous studies have demonstrated, spaceflight seemed to increase the noggin's cerebrospinal fluid, a clear liquid that acts as a cushion for your brain during motion or impacts and helps maintain the correct pressure.

“We were designed for standing in gravity on Earth, and once that force is released, all the bodily fluids move upward,” says study author Peter zu Eulenburg of the Ludwig Maximilian University of Munich. The latest study suggests that the excess cerebrospinal fluid seems to compress the brain's grey matter—the dark-colored neural tissue that contains nerve fibers and nerve-cell bodies. Though the brain largely bounced back after seven months on Earth, some effects seemed to linger.

The brain's white matter, which is primarily made of nerve fibers, initially appeared unchanged. Yet in the months after the cosmonauts' return to Earth, the volume seemed to shrink. The researchers speculate that the culprit is again cerebrospinal fluid. For the white matter, the increased pressure from the fluid may have forced some of the free water normally in the brain into the delicate white matter structure. Once the cosmonauts returned to Earth, the pressure lessened, water escaped, and white matter appeared to shrink.

Long stays in space seem to impact the brain, but it's unclear if any of these changes have cognitive consequences.

Additional research is needed to determine what, if anything, these physical changes mean for cognition or psychological health. But the latest study adds to mounting evidence that life among the stars can have enduring consequences on Earth-born adventurers. Here are some of the other biological changes people headed to orbit—and maybe one day deeper into space—will need to prepare for.

Floaty fluids flatten eyeballs

Changes in cerebrospinal fluid may have another concerning effect: blurred vision. This is a common complaint of astronauts returning to Earth, and scientists initially blamed the problem on fluids floating up through the body in low-gravity living. NASA estimates that during twin astronaut Scott Kelly's 340 days in space, a two-liter soda bottle's worth of fluid traveled from his legs to his head. This effect often gives space travelers a puffy face that scientists thought might account for the eye problems.

But in 2016, researchers pinned the problem on one particular culprit—extra cerebrospinal fluid can also put pressure on the back of the eyeball, flattening the bulbous organ and causing the optic nerve to bulge. For some space travelers, returning to Earth's familiar gravitational pull resharpens their vision. But as this latest study shows, not all the cerebrospinal fluid normalizes after landing. Because of this, it seems, not all astronauts are so lucky, and there are few known treatments for space-blurred sight.

DNA differences

Earlier this year, alarming headlines about Scott Kelly's mutated DNA began making the rounds, and even Kelly himself was surprised at the news. “What? My DNA changed by 7%! Who knew? I just learned about it in this article,” Kelly tweeted. “This could be good news! I no longer have to call [Mark Kelly] my identical twin brother anymore.”

While his DNA didn't actually mutate—and his identical-twin status certainly never wavered—space did seem to impact the expression of some of his genes.

The strings of letters that make up your genes are largely useless on their own. Instead they're like blueprints for the many proteins that make up your body. To actually build something, or be expressed, certain genes must be switched on. Spaceflight seems to impact the level of this expression for some genes—especially those that play a role in the immune system, DNA repair, and bone growth. Changes to seven percent of these genes persisted for six months after Kelly returned to his home planet, according to a NASA study.

Measly muscles and brittle bones

Gravity forces Earth-bound bodies to work a surprising amount, even when you're binging Netflix on the couch. But such forces no longer apply in space. This means muscles quickly grow measly and bones become more prone to breakages. Astronauts can lose roughly one to two percent of their bone mass each month, with the greatest losses in their lower backs and legs. This loss increases blood calcium and thus the risk of kidney stones.

What Did This Cosmonaut Miss About Earth After a Year in Space?

Scientists have been aware of these dire impacts for a while, and residents of the International Space Station vigorously exercise to counteract muscle and bone loss in low-gravity life. Diet changes, with emphasis on calcium- and vitamin D-rich foods, also help reduce the risk. (Learn about why glove design can also cause astronauts' fingernails to fall off.)

But there's only so many ways that space dwellers can work out—and there's still a readjustment period once they're grounded on Earth. “Just holding my head up is a bizarre new experience,” astronaut Chris Hadfield told CBC News after his 2013 stay on the ISS. “I haven’t had to hold my head on top of my neck for five months.”

Springy space sperm

Though there are many negative effects of space, there's one thing future space travers may not have to worry about: baby making. One 2017 study found that after nine months in orbit, freeze-dried mouse sperm could still produce healthy litters of baby mice.

Of course, having sex in space may still pose a problem. No one has yet admitted to testing this, but the low-gravity physics are not in our favor. Still, the results of the mouse study suggest that assistive reproductive technologies could help future generations populate other planets. 

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