As astronauts adapt to the weightlessness of space, their brains change in a process that mimics aging but happens at a much faster pace, new research shows. The changes were seen in the brain’s white matter, the mass of nerve cells that are allow communication within the brain by sending and receiving signals between brain cells. The researchers also found that astronauts’ brains shifted within their skulls, consistent with shifts of fluids found more generally within the body. The magnitude of these shifts increased with the number of missions astronauts were on, regardless of the total time they spent in space. The study was published January 23, 2019 in JAMA Neurology .
“The white matter changes were primarily in regions that control movement and process sensory inputs,” said Rachael Seidler, a professor of applied physiology and kinesiology at the University of Florida, and a coauthor of the study. When the human body is weightless in Earth orbit, the usual cues of gravity are missing, which could alter the typical inputs from senses. For example, the vestibular system provides people with a sense of balance and an awareness of how they are oriented in space. “A portion of the vestibular system also depends upon gravity for its signaling, so these inputs are also altered,” Seidler told Psychology Today .
“The white matter changes were in the same direction as what you would see with aging, and largely reflected deterioration,” said Seidler. Moreover, these changes in microgravity happened more quickly than changes associated with the normal aging process on Earth. Astronauts with greater changes in white matter also showed more impaired balance after the mission was over.
Seidler and her colleagues studied these changes using diffusion magnetic resonance imaging (dMRI), analyzing data collected by NASA between 2010 and 2015. Of the 26 astronauts whose dMRI scans were released by NASA’s Lifetime Surveillance of Astronaut Health, 15 had scans taken both before and after their missions, and these paired preflight and postflight scans were compared in the recent study. Seven of these 15 astronauts had completed a space shuttle mission lasting a month or less, and 8 had finished a long-duration mission on the International Space Station lasting 200 days or less. Three of the astronauts were women and 12 were men.
Dr. Rachael Seidler, professor of applied physiology and kinesiology at the University of Florida. Source: Courtesy of Heather McGregor
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The Shifting Brain
In addition to showing changes to the white matter, the dMRI scans also revealed movement of free water within the skull. “The brain sits higher in the skull following spaceflight due to the headward fluid shift that occurs in the microgravity environment," Seidler explained. “There is also more ‘room’ for free water around the base of the brain, where we observed the free water accumulation.”
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This change of the distribution of free water around the brain is consistent with the overall shift of fluids in the body in microgravity, which is evident simply looking at astronauts. “There is increased fluid in the upper half of the body resulting in visible ‘puffy face’ and thinner legs of crewmembers inflight,” Seidler said.
Greater fluid shifts within the skull were seen in more experienced astronauts. But it wasn’t simply a matter of how long they had been in space, but instead how many times they had been on space missions. “We have found some associations with the number of times that individuals have previously been to space, regardless of the number of days that they have spent,” Seidler said. “This suggests that the number of gravitational transitions may be important.”
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Once astronauts have returned to Earth and regained their sense of balance, do they still show changes to their brains? It’s too early to say. Seidler and her team are collecting additional data to look for changes in astronauts’ brains six months after they return to Earth, which will help assess the long-term impact of weightlessness.
In an additional follow-up, researchers will study space missions lasting longer than 200 days. “Since we found some associations between brain changes and mission duration, it will be important to study how longer flights, up to one year and greater, impact the brain,” Seidler noted.
Astrocytes and the Plastic Brain
Ultimately, Seidler hopes this research can help develop treatments back on Earth. “There are several conditions on Earth that impact vestibular and somatosensory processing, including healthy aging,” she said. “A better understanding of how the brain responds to altered sensory signaling may lead to new interventions.”