At the dawn of human spaceflight, we weren’t even sure people would be able to eat in space. Today, we’ve moved on to bigger questions like, “what happens to your brain in space?” This is what researchers at the University of Michigan wanted to know when they scanned the brains of a few dozen astronauts. They found some interesting, consistent changes to the shape of the brain.

The study used MRI scans of a total of 26 astronauts. 12 of them were in space for just two weeks on shuttle missions back before that program was cancelled. The remaining 14 were on the International Space Station for as long as six months. Interestingly, all the subjects experienced the same additions and losses of gray matter (the outer layer of brain tissue), but the extent of the effect varied based on how long they were in a weightless environment.

The team saw in the MRI images a consistent loss of gray matter across all subjects. This was chalked up to the way microgravity affects the body itself. Without the pull of gravity, cerebrospinal is not pulled down the spinal cord. This leads to a “puffy” appearance that astronauts tend to get. It may also cause a shift in brain density from compression.

The University of Michigan team believes the expansions of gray matter in certain regions is due to actual activities in space and how the brain copes with them. Parts of the brain that control and process sensory input from the lower extremities had marked growth in all study participants, even those who were in space for only a short time. The researchers believe this is due to the brain essentially re-learning how to move the legs in freefall, and astronauts are experiencing this every moment they are in space.

The study does not indicate whether the changes in the brain actually result in different functionality. For that, cognitive and motor tests would need to be administered before and after spaceflight. That’s on the agenda for future studies. U of M researchers also want to determine if these brain changes are permanent or if they’ll be reduced over time once back on Earth. This is currently an open question, as most of those in the shorter exposure group were in space back in the Space Shuttle days.

A better understanding of astronaut brains could help scientists figure out how neuroplasticity works. That may have a profound effect on treating neurological disease here on Earth.