By Amy Norton
WEDNESDAY, Nov. 1, 2017 (HealthDay News) -- The brains of astronauts who spend months in space appear to shift upward inside their skulls by the time they return to Earth, a new study finds.
The repercussions, if any, are uncertain for now, researchers said.
It's not clear how quickly the brain might settle back into its rightful place once Earth's gravity has taken hold, said lead researcher Dr. Donna Roberts.
And in fact, it's already known that some astronauts have returned from the International Space Station with vision problems. NASA has dubbed the phenomenon "visual impairment and intracranial pressure" syndrome, or VIIP.
Roberts said her team suspects the brain's upward shift can help explain VIIP -- though it's too early to say for sure.
The findings raise other questions, according to Roberts, an associate professor at the Medical University of South Carolina in Charleston.
Specifically, what might happen to the human brain during deeper space travel? That's a possibility in the not-too-distant future, as NASA has laid out plans for getting humans to Mars by the 2030s.
"If we see these brain changes after a few months on [the space station]," Roberts said, "what might happen on a mission to Mars?"
A journey to Mars can take three to six months. Then, to reduce travel time between the Earth and Mars, the two planets need to be aligned favorably, which occurs approximately every two years, Roberts explained.
The study findings, published Nov. 2 in the New England Journal of Medicine, are based on MRI brain scans of 34 astronauts. Eighteen had been on space station missions, averaging 165 days; the rest had been on shuttle missions, averaging 14 days.
All the astronauts had brain scans taken before the mission, then again about a week after they'd returned.
The researchers were able to look for certain structural changes in a subgroup of 18 astronauts. It turned out that all 12 space station astronauts showed an upward shift in the brain, versus none of the six who'd returned from a short-term mission.
Similarly, the space station astronauts were much more likely to show a narrowing in the cerebrospinal fluid spaces at the top of the brain.
Rachael Seidler, a professor at the University of Florida in Gainesville, is leading a NASA-sponsored study looking into the effects of prolonged spaceflight on movement, thinking and behavior.
She described the dynamics of what the latest study showed in basic terms: The Earth's gravitational pull normally draws fluids downward in the body. But in the microgravity of space, more cerebrospinal fluid can build up around the brain -- which pushes it up.
"In a sense, the brain is getting a little squished," Seidler said.
More work is needed to know what it all could mean.
"How long do the [brain] changes last?" Seidler said. "Are there effects on behavior or physical performance?"
Astronauts have, of course, been traveling to and from space for decades. And scientists have long studied the effects on the heart, bones and other body systems, Roberts said.
The brain, however, has gotten little attention.
That started changing in recent years, Roberts said, with the emergence of VIIP -- which has cropped up almost exclusively after long-term missions.
But the questions go beyond VIIP, according to Seidler.
For example, she said, what happens when the brain is no longer getting normal sensory information from the legs for months? What are the effects of having the vestibular (balance) system thrown off by being in microgravity 24/7?
Studying those questions, Seidler said, could help in better understanding earthly conditions, too -- such as cases where people are on prolonged bed rest.