By Jamie Talan December 5, 2019

Brain MRI scans revealed cognitive and movement changes in astronauts who participated in long space flights. Researchers advise advanced neuroimaging protocols and long-term follow-up imaging in this population.

Astronauts who have participated in long space flights appear to have structural alterations in the brain that are associated with changes in measures of cognition and movement about a month after they return to Earth's atmosphere, suggests a study published online October 17 in the American Journal of Neuroradiology.

Our findings support the need for advanced neuroimaging protocols and long-term follow-up imaging of the astronaut population, the study authors wrote. Most important, understanding the influences of gravity on CSF homeostasis and brain health may provide insights into abnormalities of CSF homeostasis such as idiopathic normal pressure hydrocephalus.

In the retrospective study, Donna Roberts, MD, associate professor of radiology at the Medical University of South Carolina, and her colleagues looked at brain MRI scans from 19 NASA astronauts who had scans done before an International Space Station mission or a Space Shuttle flight and again after they returned. The scientists also had access to pre- and post-clinical assessments and tests conducted to identify cognitive and movement changes.

They found a significant 10.7 percent change in total ventricular volume in astronauts who returned from long-duration International Space Station (ISS) missions compared with no changes in ventricular volume in astronauts who returned from short-duration Space Shuttle missions.

Dr. Roberts met earlier in November with NASA scientists to discuss the findings. I believe NASA should make this a priority, she said. We need to understand what changes to brain structure and physiology are occurring during these long-duration spaceflights, whether or not these changes have any clinical consequences and, if so, then in what ways can we protect against these changes. We also don't know whether these brain changes persist after some time back in the gravity environment of Earth.

In a 2017 study in The New England Journal of Medicine, the South Carolina scientists looked at the MRI results from long-duration flights and found enlargement of the ventricles, an upshift in the brain, and a narrowing of the cerebrospinal fluid spaces at the top of the brain. The brain tissue seemed crowded, Dr. Roberts explained. With this observation in hand, she and her colleagues returned to the NASA files to obtain performance data that they could use to see if it matched with the MRI changes.

The scientists worked with data provided by the NASA Lifetime Surveillance of Astronaut Health office. They received pre-and-post flight MRI scans on 12 astronauts who spent time on the ISS and seven others who made shorter shuttle missions. Four of the astronauts on the ISS mission had spaceflight-associated neuro-ocular syndrome (SANS), which is characterized by changes to the retina that alter visual acuity and swelling of the optic nerve. These visual problems were first identified in 2005 and prompted NASA to add brain scans to a long list of tests to understand the health effects of space flight. The agency has been collecting MRI data for about a decade. Some of the astronauts had consented to a lumbar puncture, as well, that was used to measure intercranial pressure. When ISS astronauts touched down in Kazakhstan to begin their re-adaptation to the Earth's atmosphere, crew members put them through a series of tests to measure their motor skills. They assessed whether the astronauts could climb a ladder, open a hatch, get out of a seat and maneuver an easy obstacle course, and maintain their balance when carrying out these tasks.

Dr. Roberts and her team also had access to pre- and post-flight cognitive data that are now being collected on all astronauts who complete a mission. Both these post-flight functional and cognitive tests were done within a few days of re-entry. The MRI scans were also done within a few days of re-entry.

The scientists reported a 10.7 percent increase in the total ventricular volume post-flight compared with preflight in the ISS astronauts. There was no change in the shuttle astronauts. They reported that the younger astronauts were more likely to have enlarged ventricles on MRI, and the MRI findings were negatively correlated with the visual deficits of SANS, which tends to occur in older astronauts. The percentage of ventricle change was greater in those who participated in longer missions. There were no significant changes on pre- to postflight in the total volume of gray matter or white matter for either the Shuttle or ISS astronauts. The team also had access to cognitive testing data, primarily the Spaceflight Cognitive Assessment Tool for Windows (WinSCAT). This test was developed by NASA as a screening tool to monitor cognitive status during missions so flight surgeons could identify any performance issues. They analyzed data from sub-tests of the WinSCAT, including tests that measured speed and efficiency, memory, working memory, mathematical processing, and sustained attention.

They did not see a change in pre- and post-flight scores or an association between performance on the test and the length of the mission. They did find that astronauts showed a decrement in accuracy on processing speed and learning tests but showed faster reaction times on a subset of tests on sustained attention. They were also able to link it to changes in volume in three white matter regions on the scans.

The researchers found that the structural changes in the left caudate nucleus correlated with a worsening on tests of balance control. That does not mean that these volume changes caused these problems, Dr. Roberts said, and no one knows whether the structural changes persist over time.

We are trying to raise awareness so that NASA can better understand what happens to the brain in space, Dr. Roberts added. We have no idea whether these changes are a positive adaptive response to space flight, or a maladaptive consequence. As we send more astronauts into space and with the rising interest in space tourism we want to make sure we understand what is happening to the human brain in space. We will be able to develop countermeasures but we first need to understand what is happening.

There is a lot we don't know about what is happening to the brain in space, said Stephen A. McGuire, MD, FAAN, adjunct professor of neurology at the University of Texas Health Sciences Center San Antonio. It is not surprising that whatever is causing fluid shifts in the brain would be associated with changes in cognition. But you have to be careful. How much is learned behavior and remodeling of the brain and how much is environmentally-induced structural change? The ataxia that astronauts experience may just be a part of readjusting to gravity. Are these permanent changes? Astronauts are very high performers, which makes it difficult to appreciate any long-term effects. We just don't know.

Dr. McGuire has studied the effects of high altitude on U2 pilots and identified long-term deficits in cognition (following a five to 15-year period of extreme hypobaric exposure) that were correlated with white matter changes compared to Air Force pilot controls. But, he said, the effects were not clinically significant.

There are lots of unanswered questions, Dr. McGuire said. How significant are these problems in the astronauts and is this something we really need to be concerned about?

Jonathan B. Clark MD, MPH, associate professor of neurology and space medicine in the department of neurology in the Center for Space Medicine at Baylor College of Medicine, said that one of the problems in studying long-term effects of space flight on the brain is getting access to astronauts. They had small numbers but it bears further consideration and evaluation. The fact that they correlated these ventricular changes with cognitive and motor behaviors tells us that we need to keep an eye on this.

Also, he said, part of the problem with the data is that the MRI scans were generally done in the first three weeks after landing and the functional tests are done within the first few days. And during those first few days, they are landing in Kazakhstan and immediately flown to Russia and then to the United States. They are back in the US within 48-hours and you can imagine that they have the weight of gravity to contend with and the multiple flights.

It is a fascinating finding, he said. Space changes all organ systems so it would not be surprising that the brain would be affected, cautioning that they may still be in an adaptive phase. The scientists did not find any gray or white matter changes and that would be when you worry. The functional effects will generally recover after a week or two. The anatomy is arguably what will change slower.

He said that NASA is now evaluating 24 cases of SANS. This study only captured four of these cases.

Jennifer Fogarty, PhD, is the chief scientist for NASA's human research program, and oversees a portfolio of studies on astronauts during space: How their bodies change and adapt and whether the changes could create a health or performance risk. The key is interpreting the change on brain imaging scans, she said of the Medical University of South Carolina study. They identified a correlation but that doesn't tell us if it is causality.

The ataxia that astronauts experience may just be a part of readjusting to gravity. Are these permanent changes? Astronauts are very high performers, which makes it difficult to appreciate any long-term effects. We just don't know.

DR. STEPHEN MCGUIRE

She said that the agency has been trying to understand SANS and design ways to protect against it during long-term spaceflight. NASA has neurologists, neuroscientists, and neuro-ophthalmologists assessing the SANS data we collect. So far, nothing has reached a clear clinical threshold.

Dr. Fogarty said that NASA engineers are designing devices to use lower body negative pressure to pull blood volume and CSF back down. The device will be tested in 2021. There are also ongoing studies to see whether elevated CO2 levels on the Space Station help contribute to changes in the eye.

Using data like this, she said, referring to the Medical University of South Carolina study, helps us to go in different directions.

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Prolonged Space Flight Affects Human Brain Structure and... : Neurology Today - LWW Journals