An astronauts brain will compress and expand during spaceflight, according to a new study from the University of Michigan.

Researchers found that the brain has increases and decreases in gray matter volume while in space, which is equivalent to someone on Earth practicing a new skill round-the-clock.

During the study, 13 astronauts who spent two weeks as shuttle crew members were given structural MRIs, as well as 14 astronauts who spent six months on the International Space Station. The astronauts ranged from zero days in space to 300 days in space.

According to the study, the astronauts experienced extensive volumetric gray matter decreases, including large areas covering the temporal and frontal poles and around the orbits, with a larger effect seen in the International Space Station astronauts in some regions.

One of the areas the researchers found increases in gray matter volume was in regions of the brain that control leg movement and process sensory information from the legs, which may reflect changes related to the brain learning how to move in microgravity.

These changes were greater in the astronauts from the space station because their brains were learning and adapting at all times while in space.  

Principal investigator Rachael Seidler, a professor of kinesiology and psychology at the University of Michigan, described the results of the study.

“We found large regions of gray matter volume decreases, which could be related to redistribution of cerebrospinal fluid in space,” Seidler said in a statement. “Gravity is not available to pull fluids down in the body, resulting in so-called puffy face in space.

“This may result in a shift of brain position or compression,” he added.

According to the study, humans undergo extensive sensorimotor adaptation during spaceflight due to altered vestibular inputs and body unloading.

The study was the first to examine structural changes that take place in astronauts’ brains during spaceflight.

While scientists have not yet pinpointed the exact nature of the changes, the findings may result in new ways to think about certain health conditions including people on long-duration bed rest or people who have normal pressure hydrocephalus—a condition in which cerebrospinal spinal fluid accumulates in ventricles in the brain and causes pressure.

According to Seidler, brain changes could reflect new connections between neurons. She’s leading another long-term study that will help determine the repercussions on cognition and physical performance, as well as how long the brain changes last.

For example, the brain may still recruit different pathways to compensate for the structural brain changes caused by spaceflight even after balance returns.

“The behavior may return to normal, but the way the brain controls the behavior may change,” she said.

The results largely parallel findings from another study Seidler is leading on long-term bed rest where volunteers spent up to three months in downward tilted position and brains shifted up.

The study was published in Nature Microgravity.