New neuroimaging research indicates that long-duration spaceflight results in structural brain changes, which could be the result of increased intracranial pressure while exposed to low levels of gravity. The findings have been published in the journal Radiology.
“I have been working with NASA since around 2009,” explained Larry Kramer, the corresponding author of the study and a professor of diagnostic and interventional imaging at McGovern Medical School at UTHealth in Houston.
“There was an astronaut that had just returned from a mission who developed visual problems during spaceflight. NASA flight surgeons wanted more information beyond what they could see on clinical examination. They asked me to perform a high-resolution magnetic resonance imaging study of this astronaut’s eye at the MRI research magnet at UTHSC-Houston.”
“This is how my involvement started. I was able to describe a number of abnormalities which then resulted in another 26 astronauts being scanned over several years. I have been involved in trying to understand the mechanism of injury to astronaut’s eyes since then. The current study is the evolution of original work published in 2012.”
In the current study, Kramer and his colleagues examined the brain structure of 11 astronauts, including 10 men and one woman, before they traveled to the International Space Station. The researchers followed up with MRI studies 1, 30, 90, 180, and 360 days after the astronauts returned. The astronauts spent 171 days in space on average.
The researchers observed expansions in the astronauts’ combined brain and cerebrospinal fluid (CSF) volumes. There was also increased velocity of CSF flow through the cerebral aqueduct, a narrow channel that connects the ventricles in the brain.
“Microgravity causes alteration of both the eye and brain. In the brain, this is predominantly in the form of expansion of the volume of the white matter compartment and to a lesser degree enlargement of the fluid file spaces in the center of the brain (ventricles). Our current study showed that these changes persist up to one year postflight and therefore may be permanent,” Kramer told PsyPost.
However, the researchers noted that “the changes are small in magnitude and remain within the range for healthy adults of similar age.”
The brain scans also showed alterations to the pituitary gland, with most of the astronauts showing evidence of pituitary gland deformation, which suggests elevated intracranial pressure during spaceflight.
“We found that the pituitary gland loses height and is smaller postflight than it was preflight,” 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 study — like all research — includes some limitations.
“The major caveat is that we are not able to obtain MRI data in orbit to know the true extent of changes that are occuring in the brain while in the microgravity environment. All MRI studies are performed preflight and postflight only. This void is partially filled by optical coherence tomography and ultrasound,” Kramer explained.
It is also unclear what causes the brain and ventricles to swell.
“The predominant theory is that redistribution of fluid from the lower extremities headward is the precipitating cause. We are working with creating negative pressure in the lower extremity and full body artificial gravity through centrifugation to see if these interventions will prevent changes in the brain and orbit from occurring. These interventions are currently being evaluated in microgravity analogue studies performed on earth,” Kramer said.
The study, “Intracranial Effects of Microgravity: A Prospective Longitudinal MRI Study“, was authored by Larry A. Kramer , Khader M. Hasan, Michael B. Stenger, Ashot Sargsyan, Steven S. Laurie, Christian Otto, Robert J. Ploutz-Snyder, Karina Marshall-Goebel, Roy F. Riascos, and Brandon R. Macias.