Tallahassee: Living in microgravity conditions during spaceflight can cause the human brain to shift upward and backward and undergo subtle deformation inside the skull, according to new research.

The study, based on MRI scans of 26 astronauts who spent varying durations in space, found that the extent of brain movement increased with longer missions. Astronauts who stayed aboard the International Space Station for about a year showed more pronounced shifts in specific brain regions compared to those on shorter missions.

Researchers said the changes occur because the absence of gravity in space alters the normal balance of fluids in the body, causing them to move toward the head. This disrupts the usual equilibrium between the brain, cerebrospinal fluid and surrounding tissues.

The study noted that regions involved in movement and sensation experienced the largest shifts, with some areas near the top of the brain moving upward by more than two millimetres. Most changes gradually reversed within six months of return to Earth, though some backward shifts persisted longer.

The findings, researchers said, are important as space agencies plan longer missions and expand human space travel.