This article was originally published on The conversation.
Going to space is hard on the human bodyand as a new study from our research team findsthe brain shifts upwards and backwards and is deformed inside the skull after space travel.
Why it matters
On Earth, gravity constantly pulls fluids in your body and brain toward the center of the Earth. In space, that power disappears. Body fluids shift toward the head, giving astronauts a swollen face. Under normal gravity, the brain, cerebrospinal fluid and surrounding tissues reach a stable balance. In microgravity, that balance changes.
Without gravity pulling down, the brain floats in the skull and experiences various forces from the surrounding soft tissue and the skull itself. Previous studies showed that the brain appears higher in the skull after space travel. But most of these studies focused on average or whole-brain measures, which may obscure important effects within different areas of the brain.
Our goal was to take a closer look.
How we do our work
We analyzed MRI scans of the brain from 26 astronauts who spent varying lengths of time in space, from a few weeks to over a year. To focus on brain movement, we aligned each person’s skull across scans taken before and after spaceflight.
That comparison allowed us to measure how the brain shifted in relation to the skull itself. Instead of treating the brain as a single object, we divided it into more than 100 regions and tracked how each had shifted. This approach allowed us to see, on average, patterns that were missed when looking at the whole brain.
We found that the brain consistently moved upwards and backwards when we compared postflight to preflight. The longer someone stayed in space, the greater the shift. One of the more striking findings came from examining individual brain regions.
In astronauts who spent about a year aboard the International Space Station, some areas near the top of the brain moved upward by more than 2 millimeters, while the rest of the brain barely moved. That distance may sound small, but inside the tightly packed space in the skull it is meaningful.
Areas involved in movement and sensation showed the largest shifts. Structures on the two sides of the brain moved toward the midline, meaning they moved in opposite directions for each hemisphere. These opposing patterns cancel each other out in whole-brain averages, which explains why previous studies missed them.
Most displacements and deformations gradually returned to normal within six months of return to Earth. The backward shift showed less recovery, probably because gravity pulls downward rather than forward, so some effects of spaceflight on brain position may last longer than others.
What’s next
NASA’s The Artemis program will mark a new era of space exploration. Understanding how the brain reacts will help researchers assess long-term risks and develop countermeasures.
Our findings do not mean that people should not travel to space. While we found that larger shifts in the location of a sensory-processing brain region correlated with balance changes after the flight, the crew members did not experience obvious symptoms—such as headaches or brain fog—related to changes in brain position.
Our findings do not reveal immediate health risks. Knowing how the brain moves in space and then recovers allows scientists to understand the effects of microgravity on human physiology. It can help space agencies design safer missions.
