Astronaut Brain Changes: How Space Travel Impacts Brain Structure & Function

Astronauts returning from extended stays on the International Space Station (ISS) are experiencing measurable and lasting changes to their brain structure, according to research published this week in the journal PNAS. The findings, based on magnetic resonance imaging (MRI) of 26 astronauts, have prompted NASA to reassess the potential risks of long-duration spaceflight as it plans missions to the Moon and beyond.

The study, conducted by researchers Rachael Seidler and Tianyi Wang at the University of Florida, reveals that the brain does not remain stationary within the skull in the absence of Earth’s gravity. Data indicates a systematic upward and backward shift in brain position, with the magnitude of the displacement increasing with the length of time spent in orbit. This “floating” effect occurs as bodily fluids redistribute towards the head in microgravity, altering internal pressures within the cranium, researchers explained.

For decades, it was assumed the brain was relatively immune to the mechanical changes of space, but the MRI analysis challenges that understanding. “When humans return from space, their average brain position is higher within the cranial compartment,” stated Wang and Seidler in their published work. “The brain shifted backward, upward, and rotated backward in the direction of tilt between pre- and post-spaceflight.”

Researchers divided the brain into over 100 distinct anatomical regions to precisely measure these movements, comparing pre-flight and post-flight scans. In astronauts who spent nearly a year on the ISS, some brain regions shifted more than two millimeters. Even as seemingly small, this displacement is considered significant given the limited space within the skull and its potential biomechanical impact.

The areas of the brain most affected by these shifts are those linked to movement and sensory perception. The study also found that structures in both hemispheres tended to move closer to the midline, a phenomenon that could have been overlooked in analyses focusing on overall averages.

A recent incident where NASA was forced to bring an astronaut back from the ISS early due to a medical issue underscores the growing concern over the physiological effects of space travel. While the specific health problem of that astronaut has not been disclosed, the timing coincides with the release of this new research.

Whereas most of these alterations tend to reverse within six months of returning to Earth, the backward shift appears to show less recovery. Understanding how microgravity impacts the human brain is now considered essential for NASA as it develops strategies for safer, longer-duration missions. According to the researchers, these findings do “not imply that people should not travel to space,” but rather highlight the need for further investigation and mitigation strategies.

The research comes as NASA continues to study the genetic makeup of astronauts, exploring ways to enhance their resilience, even looking at the extraordinary hardiness of tardigrades – microscopic animals known for surviving extreme conditions – as a potential model.