Astronauts’ brains shown to physically change after long periods in space
Image credit: NASA
Extended periods in space could have effects on the brains of astronauts, including a reduction in overall brain matter and deformation of pituitary glands, researchers have said.
Health problems among astronauts have been known for some time. More than half of the crew members on the International Space Station (ISS) have reported changes to their vision following long-duration exposure to the microgravity of space.
There is also evidence to suggest that low-gravity conditions can cause “leaky” gut problems, even after removal from a microgravity environment.
With this in mind, researchers in the US carried out MRI scans on 11 astronauts - 10 men and one woman - before they travelled to the ISS. This was followed by further MRI studies one day after the astronauts returned from space, then at several intervals throughout the following year.
“When you’re in microgravity, fluid such as your venous blood no longer pools toward your lower extremities, but redistributes headward,” said Larry A. Kramer, study lead author from the University of Texas Health Science Center at Houston. “That movement of fluid toward your head may be one of the mechanisms causing changes we are observing in the eye and intracranial compartment.”
The MRI results showed that the long-duration microgravity exposure caused expansions in the astronauts’ combined brain and cerebrospinal fluid (CSF) volumes.
CSF is the fluid that flows in and around the hollow spaces of the brain and spinal cord. The combined volumes remained elevated at one-year postflight, suggesting permanent alteration.
“What we identified that no one has really identified before is that there is a significant increase of volume in the brain’s white matter from preflight to postflight,” Kramer said. “White matter expansion in fact is responsible for the largest increase in combined brain and cerebrospinal fluid volumes postflight.”
The MRI scans also showed alterations to the pituitary gland, a pea-sized structure at the base of the skull often referred to as the “master gland” because it governs the function of many other glands in the body. Most of the astronauts had MRI evidence of pituitary gland deformation, suggesting elevated intracranial pressure during spaceflight.
“We found that the pituitary gland loses height and is smaller postflight than it was preflight,” Dr. Kramer said. “In addition, the dome of the pituitary gland is predominantly convex in astronauts without prior exposure to microgravity, but showed evidence of flattening or concavity postflight. This type of deformation is consistent with exposure to elevated intracranial pressures.”
The researchers also observed a postflight increase in volume, on average, in the astronauts’ lateral ventricles - the spaces in the brain that contain CSF.
However, the overall resulting volume would not be considered outside the range of healthy adults. The changes were similar to those that occur in people who have spent long periods of bed rest with their heads tilted slightly downward in research studies simulating headward fluid shift in microgravity.
Additionally, there was increased velocity of CSF flow through the cerebral aqueduct, a narrow channel that connects the ventricles in the brain. A similar phenomenon has been seen in normal pressure hydrocephalus, a condition in which the ventricles in the brain are abnormally enlarged. Symptoms of this condition include difficulty walking, bladder control problems and dementia. To date, these symptoms have not been reported in astronauts after space travel.
The researchers are studying ways to counter the effects of microgravity. One option under consideration is the creation of artificial gravity using a large centrifuge that can spin people in either a sitting or prone position. Also under investigation is the use of negative pressure on the lower extremities as a way to counteract the headward fluid shift due to microgravity.
Dr. Kramer said the research could also have applications for non-astronauts.
“If we can better understand the mechanisms that cause ventricles to enlarge in astronauts and develop suitable countermeasures, then maybe some of these discoveries could benefit patients with normal pressure hydrocephalus and other related conditions,” he said.
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