Spaceflight may shift an astronaut's brain position and shape

A PNAS study using MRI data found that the brain tends to shift upward and backward and rotate after spaceflight, with larger changes after longer missions; most movement recovered over about six months though some differences persisted.

Researchers published findings in the Proceedings of the National Academy of Sciences reporting that time in space is associated with small shifts in average brain position and shape. The team analyzed MRI scans from 26 astronauts and 24 participants in a long-duration head-down tilt bed rest study. They aligned skull position across timepoints and used rigid body registration to quantify how the brain moved from before to after spaceflight or bed rest. The paper noted that sensory and motor regions showed the largest shifts, and that changes tended to correlate with how long a person was in microgravity. Key findings: - The brain shifted upward and backward and rotated backward in the pitch direction after spaceflight and bed rest, according to the study. - Changes correlated with exposure duration, with yearlong missions showing the largest shifts and shorter missions showing smaller effects. - The measured movement was on the order of a few millimeters in some regions, which the authors described as visible on inspection. - Most deformation recovered across three dimensions, especially the up–down direction, over about six months after return, but some differences remained for some individuals. - Reported functional effects included temporary sensory conflicts in flight and balance issues after return; the study did not find widespread serious cognitive impairment or persistent headaches in the sample. Summary: The study links microgravity exposure to measurable shifts in brain position and shape that grow with mission length and largely diminish within six months, though some residual changes persisted in a subset of participants. Undetermined at this time are the longer-term clinical implications and how recovery timelines might differ for other planetary gravity environments.