It’s easy to imagine a future where humans travel freely through space, visiting places like the Moon and Mars to carry out research or perhaps even set up colonies. There are many technological hurdles to scale before such a future is even remotely possible, but what about the biological impacts on our own bodies? Scientists aimed to answer some of those questions and a new paper published in Radiology reveals one very interesting effect of long-term spaceflight: Human brains get physically bigger.

The research has led to some very important questions about how well-suited humans are for space travel and what kind of long-term effects travelers to the Moon, Mars and beyond, may experience.

For the study, researchers performed MRI brain scans on 11 astronauts before they spent time on the International Space Station. After returning, the astronauts were once again scanned and the before-and-after images were compared.

The left image shows an astronaut’s brain before their mission to space and the right image shows their brain after returning from space.
The left image shows an astronaut’s brain before their mission to space and the right image shows their brain after returning from space.Larry A. Kramer et al.

Because the International Space Station is in orbit around Earth, the gravity acting on its inhabitants is minimal. Scientists have been studying the effects of microgravity on the human body for a long time and we know that blood flow is dramatically affected. Without gravity acting on a person’s body, organs experience changes too and that includes the brain.

Research has shown that areas of the brains of astronauts physically expand in space. The changes aren’t dramatic, but they are measurable and the lack of gravity is likely to blame.

“When you’re in microgravity, fluid such as your venous blood no longer pools toward your lower extremities but redistributes headward,” Dr. Larry A. Kramer, lead author of the study, said in a statement. “That movement of fluid toward your head may be one of the mechanisms causing changes we are observing in the eye and intracranial compartment.”

In this new round of research, scientists wanted to know how long this effect lasts after the astronauts returned to Earth. With the normal amount of gravity acting on their bodies, would the changes in the brain be reversed?

It doesn’t appear so. Even a full year after returning to Earth, the brains of the astronauts involved in the study remained at their postflight size, suggesting that the changes may be permanent.

It’s still unclear exactly what this means for the astronauts and future space travelers. The researchers noted changes in the shape of the pituitary gland which they attributed to the increased pressure in the brain cavity. Changes to the flow of cerebrospinal fluid were also noted, though the astronauts don’t report symptoms and would seem to be healthy.

NASA and other space agencies are working on ways to mitigate the physical effects of spaceflight on the human body and these new techniques will be increasingly important if we hope to send humans on long-distance missions in our solar system.