The microgravity of space appears to shift the location of astronauts’ brains, with no obvious effect on their health
By Rachel Seidler, Tianyi (Erik) Wang & The conversation in the United States
Gong, Chen
The following essay is reproduced with permission from 
The conversationan online publication covering the latest research.
Go to space is hard on the human bodyAnd like a new study Since our research team findthe brain moves up and back and becomes deformed inside the skull after spaceflight.
The magnitude of these changes was greater for those who spent more time in space. As NASA plans longer space missions and space travel expands beyond professional astronauts, these findings will become more relevant.
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Why it matters
On Earth, gravity constantly pulls fluids from your body and brain toward the center of the Earth. In space, this force disappears. Body fluids move toward the head, giving astronauts a swollen face. Under normal gravity, the brain, spinal fluid, and surrounding tissues reach a stable equilibrium. In microgravity, this balance changes.
Without gravity pulling downward, the brain floats within the skull and experiences various forces from surrounding soft tissues and the skull itself. Previous studies have shown that the brain appears higher in the skull after spaceflight. But most of these studies focused on average or whole brain measurements, which may mask important effects in different areas of the brain.
Our goal was to take a closer look.
How we do our work
We analyzed Brain MRI of 26 astronauts who spent varying lengths of time in space, from a few weeks to more than a year. To focus on brain movements, we aligned each person’s skull with scans taken before and after spaceflight.
This comparison allowed us to measure how the brain moved 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 the evolution of each one. This approach allowed us to detect patterns that were missed on average when looking at the whole brain.
We found that the brain consistently moved up and back when comparing post-flight to pre-flight. The longer a person stays in space, the greater the shift. One of the most striking findings came from examining individual regions of the brain.
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. This distance may seem small, but within the restricted space of the skull it makes sense.
Areas involved in movement and sensation showed the greatest changes. Structures on both sides of the brain shifted toward the midline, meaning they moved in the opposite direction for each cerebral hemisphere. These opposing patterns cancel out in whole-brain averages, which explains why previous studies have not detected them.
Most displacements and deformations gradually returned to normal six months after returning to Earth. The backward shift showed less recovery, likely because gravity pulls downward rather than forward, so some effects of spaceflight on brain position may last longer than others.
What’s next
from NASA Artemis Program will mark a new era of space exploration. Understanding how the brain reacts will help scientists assess long-term risks and develop countermeasures.
Our findings don’t mean people shouldn’t travel to space. Although we found that larger shifts of a sensory processing brain region correlated with balance changes after the flight, crew members did not experience overt symptoms – such as headaches or brain fog – related to the changes in brain position.
Our results do not reveal any immediate health risks. Knowing how the brain moves during spaceflight and then recovers allows researchers to understand the effects of microgravity on human physiology. This can help space agencies design safer missions.
THE Research summary is a brief overview of interesting academic work.
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