The first humans traveled to space over 60 years ago. And, for over 20 years, humans have been living and working in space aboard the International Space Station. Now, we are making plans to send humans to Mars. However, to get people safely to Mars, scientists still need to understand more about how space travel impacts the human brain and body. Our lab has spent the last 10 years studying how spaceflight affects astronauts’ brains and their walking, balance, and coordination.

What Is Different in Space?

Astronauts face many challenges in space [1]. They must figure out how to live and move without Earth’s gravity. Imagine taking a shower or doing a science experiment while floating! In addition, the balance system in the inner ear, which is also known as the vestibular system, relies on Earth’s gravity to tell us which way is “up” (Figure 1). Astronauts often confuse “up” and “down” in space because the vestibular system does not work the same way without gravity!

An astronaut’s job is also stressful. For example, astronauts living in space spend months away from their families and friends. Astronauts also do not get the best sleep. We think that all of these things cause changes to the brain that would not normally happen on Earth. So, this was our big research goal—to understand what happens to the brain when people go to space.

What Did We Do?

We asked 15 astronauts to be in our study. They traveled to the International Space Station and lived there for 6 months to a year. We took pictures of each astronaut’s brain two times before they went to space and four times after they returned home (Figure 2A). We took these pictures using a magnetic resonance imaging (MRI) scanner (Figure 2B). The MRI scanner recorded two things: the size and shape of the astronauts’ brains, and which parts of their brains were working during various activities.

We also tested astronauts’ walking, balance, and coordination by having them perform activities like a timed obstacle course (Figure 2C), standing and balancing on a platform that tilts (Figure 2D), and putting pegs into rows of tiny holes (Figure 2E). We wanted to compare how well the astronauts did on these tests before vs. after spaceflight.

Does Spaceflight Change How Astronauts Move?

What did our research find? First, when astronauts got back to Earth, they were worse at walking, balancing, and using their hands to insert small pegs into holes than they were before they went to space [2]. We think this is because astronauts got used to moving around in a totally different environment in space—one without gravity. Because the vestibular system did not work properly without gravity, the brain “turned down the volume” of information from this system while in space. The astronauts also did not need to use their leg muscles very much to move in space—they could just float around the space station for months! These changes made it hard for them to walk normally when they got back to Earth. The astronauts’ brains had to turn the vestibular signals back up and relearn how to move in gravity.

Does Spaceflight Change How the Brain Looks?

Our next goal was to study how the brain looks after astronauts go to space (Figure 3A). We found multiple changes. First, the brain shifts up inside of the skull during spaceflight [3]. This shift squishes the top of the brain against the inside of the skull. We think that this squishing might play a role in some of the walking, balance, and coordination problems that astronauts have when they get back to Earth because brain areas involved in movement are the ones getting squished.

Second, we looked at how water in and around the brain is shifted after spaceflight. Inside the skull, the brain is surrounded by water. There are also pockets of water inside of the brain, which are called ventricles. We found that the ventricles got larger after spaceflight [3, 4]. In space, there is no gravity to “pull” water toward the feet. We think the lack of gravity causes extra water to stay inside the skull and makes it difficult for the extra water to drain out. The ventricles get bigger to help store this extra water. Right now, we are not sure if it is a bad thing that extra water stays in the brain during spaceflight, and we also do not yet know how long it takes for the ventricles to return to their normal size (if at all) when astronauts come home to Earth. So, this is definitely something that we want to study more.

Lastly, we found that astronauts who spent more time in space (like a full year) had bigger brain changes than astronauts who took shorter trips [3]. This is important because we want to plan longer space missions—but we need to make sure that people’s brains will stay healthy. For instance, a Mars mission could take almost 3 years, which is longer than any human has ever spent in space!

Does Spaceflight Change How the Brain Works?

Our last goal was to study whether spaceflight changes how the brain works. As we mentioned, when living in space, astronauts lose their sense of “up” and “down.” Since astronauts can float, this means they do not have to stand on the floor to brush their teeth, for example. They could brush their teeth while bouncing off the ceiling if they feel like it—they would not even feel like they were upside down!

We wanted to know if going to space changes the way the vestibular system works. To do this, astronauts laid in the MRI scanner, and we recorded their brain activity to see if their vestibular systems worked differently after spaceflight [5]. When astronauts returned to Earth, we found that more sensory parts of the brain got involved to help the vestibular system process information (Figure 3B). So, after spaceflight, brain areas responsible for understanding vision and touch still got involved to help the vestibular system work! We think this happens because the brain spends months in space getting used to not having Earth’s gravity. Then, when astronauts get home, they need more “brain power” to function in Earth’s gravity again.

Why is this important? These brain changes related to how well astronauts could balance after they returned home. Specifically, the astronauts who showed more brain changes could balance better post-flight. We think it is really important to understand why some astronauts adapt better than others to living in space and returning home. This could help us figure out which astronauts might need extra training before going to space or which might need the most help getting back to normal after returning home.

How Can We Study This on Earth?

Not very many people go to space, so this limits who can participate in our research studies. It took us many years to study just 15 astronauts!

So, scientists have come up with other ways to study spaceflight here on Earth. For instance, we have tested what happens to the bodies and brains of healthy people when they lay in bed—without standing up at all—for 2 months! These bed rest experiments let us study some effects of spaceflight, like how astronauts in space do not need to use their legs and feet to support their own body weight while standing and walking.

Other researchers study what happens when people fly on special airplanes that “fall” through the air for about 20 seconds at a time. This lets people on the airplane float for 20-second periods. But the problem is that 20 seconds is a really short time for researchers to study what happens without Earth’s normal gravity! So, these tests are different from tests on people who spend months in space.

Other scientists have studied what happens to people who spend the winter in Antarctica. These people cannot leave their research stations because of the unbearable temperatures outside. These studies help us understand how being very isolated and confined inside might affect people’s mental health and how their brains work.

Each of these situations can provide us with some information about how the human body might respond to spaceflight. However, nothing is as informative as actually going to space. Therefore, over the next years, scientists will need to continue studying more and more astronauts. This will give us an even better understanding of what happens to astronauts’ brains and bodies when they spend time in space.

What Is the Takeaway Message?

Overall, traveling to space seems to be generally safe for humans. When astronauts return from space, they should expect to have some temporary problems moving around, like trouble walking and balancing. With an MRI scanner, we can see that certain brain changes happen when astronauts go to space. The brain shifts up, the ventricles (water pockets) get bigger, and more “brain power” is needed to process certain information. Some of these changes take a few months or more to get back to normal after astronauts return to Earth.

Together, all our results will be really important for planning future space missions. Studying what happens to the brain in space will help us understand how humans can safely live in space. This information can also help us to develop better training and better treatments to keep astronauts healthy as we send people on longer and longer missions.

What Is Next?

There is still a lot of work to be done before we fully understand what happens to people’s brains when they go to space. But do not worry—there are a lot of people on the job! Many scientists around the world are studying how to make space travel safer.

For example, our team’s next research will follow astronauts for 5 years after they get home, to see just how long it takes for certain brain changes to recover. Overall, we hope that this work will help us better understand how to keep astronauts safe when they explore new frontiers—like Mars, or beyond!

Glossary

International Space Station: ↑ A space laboratory orbiting about 250 miles above Earth, where astronauts from various countries live and work in space.

Coordination: ↑ The ability to move parts of the body together smoothly while doing one task. The eyes and hands have trouble working together after spaceflight, but this gets better pretty quickly!

Vestibular System: ↑ The balance system, located in the inner ear, that sends information to the brain to help us balance and keep track of which way is “up” and which way is “down”.

Magnetic Resonance Imaging (MRI): ↑ A machine that uses a powerful magnet and cellphone-like waves to take pictures of specific body parts. We use MRI to take pictures of the brain.

Ventricles: ↑ Pockets inside of the brain that are filled mostly with water.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Acknowledgments

We would like to thank all of the astronauts who participated in our research. We would also like to thank the many scientists who helped with our work, including Dr. Jacob Bloomberg, Dr. Ajitkumar Mulavara, Dr. Patricia Reuter-Lorenz, Dr. Roy Riascos, Dr. Ofer Pasternak, Dr. Scott Wood, Dr. Vincent Koppelmans, Nichole Beltran, Yiri De Dios, and Igor Kofman.