The human brain shifts upward and backward, and undergoes deformation, following spaceflight, according to a new study analyzing the brain scans of astronauts. The extent of these changes correlates with the duration of time spent in space, raising questions about the long-term effects of space travel as missions become more ambitious.
Researchers analyzed magnetic resonance imaging (MRI) scans from 26 astronauts, examining scans taken both before and after their missions. The study, published in the journal PNAS, revealed a consistent pattern of brain movement. By aligning each astronaut’s skull across pre- and post-flight scans, the team was able to precisely measure the brain’s shift relative to the skull itself. Instead of treating the brain as a single unit, the researchers divided it into over 100 regions, tracking the movement of each area individually.
The findings indicate that the brain consistently moves upward and backward in space. For astronauts who spent approximately one year aboard the International Space Station, certain regions near the top of the brain shifted upward by more than 2 millimeters. Although seemingly slight, this distance is significant within the confines of the skull. Areas of the brain responsible for movement and sensation exhibited the most pronounced shifts. Structures on opposing sides of the brain moved toward the midline, a pattern that was previously obscured when analyzing the brain as a whole.
The shifts and deformations observed generally began to revert to normal within six months of the astronauts’ return to Earth. Yet, the backward shift showed less recovery, potentially due to the persistent downward pull of gravity on Earth. This suggests that some effects of spaceflight on brain positioning may be longer lasting.
The changes observed are attributed to the absence of gravity in space. On Earth, gravity constantly pulls fluids toward the center of the planet, including fluids within the body and brain. In microgravity, these fluids redistribute toward the head, causing the familiar “puffy face” seen in astronauts. This fluid shift alters the balance between the brain, cerebrospinal fluid, and surrounding tissues.
Previous research had indicated that the brain appeared higher in the skull after spaceflight, but these studies often relied on average measurements, masking the subtle shifts within specific brain regions. This new research provides a more detailed understanding of how different areas of the brain respond to the unique conditions of space.
NASA is currently planning longer duration missions through the Artemis program, and the findings have implications for assessing long-term risks and developing countermeasures. The agency similarly studies Spaceflight Associated Neuro-ocular Syndrome (SANS), a condition affecting astronauts’ vision, which may be related to the fluid shifts observed in this study.
Researchers emphasize that the findings do not necessarily indicate immediate health risks. While larger shifts in sensory-processing regions correlated with post-flight balance changes, astronauts in the study did not report experiencing symptoms such as headaches or brain fog. However, understanding how the brain adapts to spaceflight is crucial for ensuring the safety and well-being of future space travelers.
