We are already aware of many of the dangers that spaceflight can inflict on the human body. Loss of bone and muscle mass, distortions on eyeball size and function, and radiation are just a few in the long list of health consequences that can result from spending time in zero G. But one area of study that’s increasingly concerning is how space environments might damage the brain, and how microgravity itself can induce unique irregularities in brain shape and structure. A new study published in JAMA Neurology this week provides more concerning details on how spaceflight changes the brain. The findings inadvertently underscore just how little we know about the effects of space on brain health and safety, creating a worrisome specter that’s sure to grow larger as we start sending astronauts into space for years at a time.

“These brain changes were in the same direction as what you would see with aging, but they occurred at a faster speed,” says Rachael Seidler, a professor of applied physiology and kinesiology at the University of Florida, and a coauthor of the new JAMA paper. “They were greater with longer spaceflight mission durations, and larger brain changes were correlated with greater balance declines.”

The study’s findings center around the movement of intracranial fluids within the skull, as well as—for the first time —an examination of how spaceflight affects the brain’s white matter. As opposed to gray matter, which is composed largely of neuronal cell bodies and plays a significant role in muscle control and sensory perception, white matter is mostly made of fat-covered nerve fibers, passing along messages between different parts of the brain and the nervous system.

While gray matter development peaks in a person’s 20s, white matter continues to develop long after and won’t peak until middle age, creating larger concerns that spaceflight could effectively stunt or warp parts of the brain’s development in young astronauts normally thought to be fit for space missions.

It’s been well-documented that astronauts often come back to Earth feeling disoriented, experiencing and showing impairments in motor control, balance, and functional mobility and cognition. And it was already known that the brain shifts upward within the skull during spaceflight, and that the somatosensory cortex (which processes sensory information for the brain) also increases in gray matter volume. However, it’s never been completely clear how these various disturbances relate to one-another. More importantly, it’s never been understood what effect spaceflight has on white matter.

Seidler and her team developed a new technique that would allow them to quantify the fluid shifts occurring within astronaut brains using diffusion MRI (dMRI) scans that could track the movement of water molecules in the brain. Water molecule motion is limited by white matter fiber tracts in the brain, enabling the researchers to get a better sense of how white matter structure changes as a result of spaceflight.

NASA made available preflight and postflight dMRI scans of 15 astronauts taken from 2010 to 2015—seven of whom took part in a Space Shuttle mission lasting less than 30 days, and eight of whom completed a long-duration mission to the International Space Station lasting less than 200 days. The median age was 47.2, with 12 men and 3 women.

The findings weren’t all that surprising: Spaceflight decreased fluid around the top of the brain, and significantly increased fluid around the base of the brain, indicating that fluid distributions are altered by the upward shift of the brain within the skull. Moreover, the team found changes to white matter around pathways in the brain that process visual and spatial information, balance, vertical perception, and movement control. Astronauts with the most white matter changes experienced the most significant disturbances in these processes.

“It was compelling how well these results reflect the changes seen in rodents that have flown in space,” says Seidler.

There were a few encouraging signs that the human body can adapt. Astronauts who had simply gone on more missions—regardless of mission duration or cumulative days in space—experienced less drastic intracranial fluid movements. The researchers think it might be a sign the human body is capable of adapting to microgravity environments, but it requires multiple instances of transitions between environments to get there.

There’s no question NASA and other spaceflight parties want to avoid having their astronauts experience unsafe changes to their bodies in space, especially the brain. Unfortunately, the problem right now is that there is just too much of a lack of data to fully assess how bad or worrisome these changes really are. We’ve only launched a small percentage of people into space, and most have not spent more than a few months in orbit at a time.

“The consequences of these brain changes are unknown at this point,” says Seidler. “Long term follow up is important to understand how these brain changes might interact with aging and how or whether they recover over time.” Seidler and her team are in the process of collecting follow-up MRI scans that could illustrate what the recovery process looks like, but we won’t really learn anything until several months or years later.

Moreover, while fluid movements and white matter changes might be problematic for terrestrial living, an editorial published in JAMA along with the new study suggests it might actually be the brain’s way of adapting to space environments, representing “a beneficial neuroadaptive response to the spaceflight environment”, perhaps not unlike Stanley Kubrick’s 2001: A Space Odyssey.

Again, this area of research is unfortunately stuck in a catch-22. Understanding more about how the brain changes due to spaceflight requires much more extensive study of the astronauts prepared to go on these missions, even though longer and more frequent flights could prove to induce deleterious problems for these individuals down the road. NASA can’t do much more than assess the risks as the studies move forward and proceed with caution, but hopefully as the goals to expand humanity’s presence in space starts to ramp up, the research and resources allocated to these studies will increase as well.