As we enter a new era in space travel, a study examining how the human brain responds to being pulled out of Earth’s gravity shows that astronauts must wait three years after long missions for physiological changes in their brains to recover. Researchers examined brain scans of 30 astronauts before and after space travel. The findings, published Scientific Reportsshows that the ventricles of the brain enlarge significantly over longer tasks of at least six months, and that less than three years may not allow sufficient time for the ventricles to fully heal.

The ventricles are cavities filled with cerebrospinal fluid that protects, nourishes and removes waste from the brain. Mechanisms in the human body efficiently distribute fluids throughout the body, but in the absence of gravity, the fluid slides upward, pushing the brain into the skull and causing the ventricles to expand.

“We found that the more time humans spend in space, the more enlarged their ventricles,” said Rachel Seidler, professor of applied physiology and kinesiology at the University of Florida and author of the study. “Many astronauts travel to space more than once, and our study shows that it takes about three years for the ventricles to fully recover between flights.”

Based on the research, ventricular enlargement is the most permanent change seen in the brain as a result of space flight, said Seidler, a fellow of UF Health’s Norman Fixel Institute for Neurological Diseases.

“We don’t yet know for sure what the long-term health and behavioral health implications of this will be for space travelers,” he said, “so it seems like a good idea to give the brain time to recover.”

Of the 30 astronauts studied, eight were on two-week missions, 18 were on six-month missions, and four were in space for about a year. The enlargement of the ventricles subsided after six months, according to the study authors.

“The biggest jump is when you’re in space for two weeks to six months,” Seidler said. Said. “No measurable change in ventricular volume after just two weeks.”

With the growing interest in space tourism in recent years, this is good news because shorter space travels seem to cause subtle physiological changes in the brain, he said. While researchers haven’t been able to study astronauts in space for more than a year yet, the good news is that the expansion of the brain’s ventricles stopped after about six months, Seidler said.

“Given that we will eventually have humans in space for a longer period of time, we are pleased to see that the changes are not exponential,” he said. According to Seidler, the results of the study could influence future decisions about crew travel and mission planning.