Astronauts on spaceflights of long duration experience structural changes in critical regions of the brain that can be clearly seen on MRI, a new study shows.
The most interesting observation was the “upward brain shift and expansion of tissue along the top of the brain,” lead author Donna Roberts, MD, from the Department of Neurosciences and Neuroscience Research, Medical University of South Carolina in Charleston, told Medscape Medical News.
“We hypothesize that upward brain shift and expansion of tissue along the top of the brain may result in compression of adjacent venous structures along the top of the head,” she said. “While we cannot prove it yet, we suspect that this may ultimately result in a decrease in the outflow of CSF [cerebrospinal fluid] and blood from the head.”
The findings may help explain a constellation of neuro-ocular symptoms reported by some astronauts, which the National Aeronautics and Space Administration (NASA) has dubbed, visual impairment and intracranial pressure (VIIP) syndrome.
The study, with a video depicting the brain changes observed in an astronaut after a long-duration flight, was published online November 1 in the New England Journal of Medicine.
The investigators compared MRI brain scans of 18 astronauts before and after long-duration missions (mean flight time, 164.8 days) to the International Space Station and of 16 astronauts before and after short-duration missions (mean flight time, 13.6 days). The images were interpreted by readers unaware of flight duration.
Results showed a narrowing of the central sulcus in 17 of 18 (94%) astronauts after long-duration flights and in 3 of 16 (19%) astronauts after short-duration flights (P < .001).
Among 12 astronauts in the long-duration group and six in the short-duration group for whom there were MRI cine clips, upward shift of the brain occurred in all 12 of those in the long-duration group and in none of those in the short-duration group.
Narrowing of CSF spaces at the vertex occurred in all 12 of those in the long-duration group and in 1 of 6 (17%) of those in the short-duration group. These findings occurred independently of the previous flight experience of the astronauts, the authors report.
In addition, three astronauts in the long-duration group had optic-disk edema, and all three experienced narrowing of the central sulcus. A cine clip available for one of these astronauts showed upward shift of the brain.
Consequences Unclear but Concerning
“The area at the top of the brain, including the central sulcus, is a critical area of the brain,” said Dr Roberts. “In fact, it separates the region responsible for much of our motor function (the motor strip of the frontal lobe) from the region that regulates input of sensory stimuli (the sensory strip of the parietal lobe). In neuroscience, this region is considered an ‘eloquent’ area, given the critical function it plays in coordinating how we sense and interact with our environment,” she explained.
“The consequences of the structural changes in this region in microgravity is unknown, but any change to a region of the brain that controls the way we sense our environment and our ability to interact with it raises concerns,” Dr Roberts said.
“This area of the brain is particularly important during adaptation to the space environment, not only because of the critical functions that are needed during the mission but also because the brain must adapt continuously, given the extreme environment in which astronauts must function.
“For example, moving around the space station requires less effort from the legs than moving an equal distance on Earth. Thus, the brain has to learn new strategies for body movement. Disturbances in the ability to carry out specific motor tasks have been found during spaceflight, particularly while simultaneously engaging in a secondary cognitive task.
“Given that the changes we see are in the region that controls all of these efforts, it may impact not just current function but the ability of astronauts to adapt to their unique environment,” said Dr Roberts.
“Our findings support the need for repeated longitudinal imaging over a longer period after spaceflight and the incorporation of advanced MRI techniques into NASA imaging protocols to determine the persistence of these changes and their relationship to the VIIP syndrome,” the investigators conclude.
The study was supported by NASA. Dr Roberts received grants from NASA during the conduct of this study.
N Engl J Med. Published online November 1, 2017. Abstract
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