Scientists studying the brains of 30 astronauts who spent from two weeks to one year on ISS have found that the longer a person stayed in weightlessness the greater the changes caused in the brain, and the longer it takes to recover.
Their findings, reported today in Scientific Reports, reveal that the brain’s ventricles expand significantly in those who completed longer missions of at least six months, and that less than three years may not provide enough time for the ventricles to fully recover.
Ventricles are cavities in the brain filled with cerebrospinal fluid, which provides protection, nourishment and waste removal to the brain. Mechanisms in the human body effectively distribute fluids throughout the body, but in the absence of gravity, the fluid shifts upward, pushing the brain higher within the skull and causing the ventricles to expand.
“We found that the more time people spent in space, the larger their ventricles became,” said Rachael Seidler, a professor of applied physiology and kinesiology at the University of Florida and an author of the study. “Many astronauts travel to space more than one time, and our study shows it takes about three years between flights for the ventricles to fully recover.”
You can read the paper here. The expansion of ventricles is a normal process due to aging, but I could not find any description in the paper noting its impact, for good or ill. Long periods of weightlessness brings it about quickly, but only temporarily.