Long-duration spaceflight may lead to "significant changes" in the structure of astronauts' brains, a U.S. study said Wednesday.
Many astronauts have been known to have experienced altered vision and increased pressure inside their heads during spaceflight aboard the International Space Station, a phenomenon known as visual impairment and intracranial pressure syndrome, or VIIP syndrome for short.
Given safety concerns and the potential impact to human exploration goals, the U.S. space agency NASA has made determining the cause of VIIP syndrome and how to resolve its effects a top priority.
"We know these long-duration flights take a big toll on the astronauts and cosmonauts," Donna Roberts, a neuroradiologist at the Medical University of South Carolina, who led the study, said in a statement.
"However, we don't know if the adverse effects on the body continue to progress or if they stabilize after some time in space," Roberts said. "These are the questions that we are interested in addressing, especially what happens to the human brain and brain function?"
In the new study, Roberts and colleagues compared the brain images of 18 astronauts who had been in space for short periods of time aboard the U.S. Space Shuttle to those of 16 astronauts who had been in space for longer periods of time, typically three months, aboard the International Space Station.
They evaluated the cerebrospinal fluid (CSF) spaces at the top of the brain and CSF-filled structures, called ventricles, located at the center of the brain.
In addition, the researchers paired the preflight and postflight magnetic resonance imaging (MRI) cine clips from high-resolution 3-D imaging of 12 astronauts from long-duration flights and six astronauts from short-duration flights and looked for any displacement in brain structure.
Study results confirmed a narrowing of the brain's central sulcus, a groove in the cortex near the top of the brain that separates the parietal and frontal lobes, in 94 percent of the astronauts who participated in long-duration flights and 18.8 percent of the astronauts on short-duration flights.
Cine clips also showed an upward shift of the brain and narrowing of the CSF spaces at the top of the brain among the long-duration flight astronauts but not in the short-duration flight astronauts.
In ground-based experiments that required participants to stay in bed and keep their heads continuously tilted in a downward position to simulate the effects of microgravity for 90 days, the team also saw evidence of brain shifting and a narrowing of the space between the top of the brain and the inner table of the skull.
These results confirmed that "significant changes in brain structure occur during long-duration space flight," the researchers said.
"More importantly, the parts of the brain that are most affected -- the frontal and parietal lobes -- control movement of the body and higher executive function. The longer an astronaut stayed in space, the worse the symptoms of VIIP syndrome would be."
To further understand the results of the study, the team planned to compare repeated postflight imaging of the brains of astronauts to determine if the changes are permanent or if they will return to baseline following some time back on Earth.
"This study represents the most comprehensive assessment of the impact of prolonged space travel on the brain," study co-author Michael Antonucci of the Medical University of South Carolina said.
"The changes we have seen may explain unusual symptoms experienced by returning space station astronauts and help identify key issues in the planning of longer-duration space exploration, including missions to Mars."
The findings were published in the New England Journal of Medicine.