Scientists are still learning how spending prolonged periods of time in the microgravity of space can affect astronauts’ health. The environment has been shown to accelerate bone density loss and the destruction of blood cells, put pressure on the eyes that can cause vision problems, andcause many more health conditions — an especially pertinent topic as NASA is in the process of evacuating an astronaut from the International Space Station due to an unspecified health crisis.
The human brain, which is suspended in clear cerebrospinal fluid inside the skull, can also be impacted by the effects of microgravity — in a surprisingly tangible way. As detailed in a new study published by an international team of researchers in the journal PNAS, the brain “shifts upward and backward within the skull following spaceflight, with sensory and motor regions exhibiting the largest shifts.”
They also found that the brain’s shape deforms in measurable ways, changes that only sometimes revert within six months after returning back to Earth.
It’s a notable new finding, once again highlighting the long-term health risks of spending prolonged time in space. Astronauts conventionally have to go through a thorough post-flight recovery program to readjust to the Earth’s gravity; staying oriented and even walking in a straight line can be difficult as the brain is forced to relearn how to interpret information from the inner ear.
While we are only beginning to understand these health effects, this evidence of brain deformation and displacement could complicate future efforts to explore the cosmos.
“The health and human performance implications of these spaceflight-associated brain displacements and deformations require further study to pave the way for safer human space exploration,” the researchers wrote.
The team analyzed MRI data from 26 astronauts and compared them to a control, MRI data collected during a “long-duration head-down tilt bed rest study.” The study involved 24 non-astronauts, who were instructed to lie down at a six-degree incline with their heads below their feet for up to 60 days.
They found that spaceflight caused the brains of the astronauts to shift both up and backward “in a fashion that correlated with exposure duration.” The brains of the bed rest study participants were found to shift backwards but not nearly as much upwards as the astronauts’ brains, indicating that spaceflight had a more pronounced effect on the brain.
The researchers found that astronauts who spent longer periods in space had more difficulties regaining their balance upon their return compared to those who embarked on shorter missions.
“The people who went for a year showed the largest changes,” coauthor and University of Florida physiology and kinesiology professor Rachael Seidler told NBC News. “There were still some changes evident in people who went for two weeks, but duration seems to be the driving factor.”
Particularly for those who spent upwards of six months in space, the changes were considerable.
“It’s on the order of a couple of millimeters,” Seidler explained, “which doesn’t sound like a big number, but when you’re talking about brain movement, it really is.”
“That kind of change is visible by eye,” she added.
While “widespread recovery occurred in all three dimensions over six months following spaceflight,” some of these deformations persisted beyond that point for some of the astronauts.
However, what surprised Seidler was the lack of any serious symptoms, including headaches or cognitive impairment, both during or after spaceflight.
Plenty of questions remain. For one, we don’t know how exactly spaceflight affects individual brain regions. We also don’t know what the exact short- and long-term health consequences of brain deformation and displacement are, either, beyond a lack of orientation.
The researchers also admitted that the sample sizes of their study were limited, meaning their findings may not be generalizable.
In short, we’re only beginning to understand how microgravity affects our brains, research that could prove invaluable once we’re ready to venture even deeper into space.
“If you’ve been on Mars with one-third Earth’s gravity, or on the moon with one-sixth Earth’s gravity, will it take three or six times as long to get back to normal?” Medical University of South Carolina assistant professor of neurology Mark Rosenberg, who was not involved in the study, asked NBC.
“Whether we care to admit it or not, we are eventually going to become a space-faring species,” he added. “It’s only a matter of time. And these are just some of the unanswered questions that we need to sort out.”
More on astronaut health: Something Is Malfunctioning With Astronauts’ Brains