By Jamie Talan
April 6, 2017
ARTICLE IN BRIEF
In magnetic resonance imaging taken before and after flights to outer space, astronauts were found to have extensive volumetric gray matter decreases in the temporal and frontal poles and around the orbits, as well as bilateral focal gray matter increases in the medial primary somatosensory and motor cortices.
A team of scientists conducted the first retrospective study on the effects of space flight on the structure of the human brain and found significant post-flight volume loss and small regions of volume gain.
In the landmark study in Nature's Microgravity published in December, researchers at the University of Michigan collaborated with NASA scientists to compare and analyze pre- and post-flight MRI data on 27 astronauts who had orbited outside of Earth's atmosphere ranging from two weeks to six months. They found extensive volumetric gray matter decreases in the temporal and frontal poles and around the orbits, as well as bilateral focal gray matter increases in the medial primary somatosensory and motor cortices.
“This was the first study to look at brain structure in flight,” said the study's senior author Rachael Seidler, PhD, professor of movement science and director of the neuromotor behavior laboratory in the School of Kinesiology at the University of Michigan. “I was surprised by the scope and magnitude of the changes. We had a stringent statistical threshold and we still saw a wide range of changes.”
Now, this same team is three years into a prospective study that they hope will help them understand the brain changes that take place in a microgravity environment and whether the changes are acute or long-lasting. Dr. Seidler said this new study will also enable them to address the mechanisms that underlie the brain changes and whether there are any worrisome or positive functional changes that they can identify.
METHODS AND FINDINGS
For the current study, the Michigan and NASA team collected T2-weighted MRI scans from the 27 astronauts, although the images were not always collected using the same protocol. They also had extensive neurosensory data on each astronaut.
Thirteen of the 27 astronauts in the retrospective study spent about two weeks on a space shuttle mission and 14 others clocked in about six months on the International Space Station mission. The ages of the astronauts ranged from 40 to 60 years old, and their time spent in space ranged between 12 and 200 days. Two of the astronauts had each spent more than 300 days on previous missions.
The researchers conducted pre- and post-flight assessments on 21 astronauts, collecting neurosensory data that included measurements of balance control. Complete data were not available on the other six. The post-flight assessments, which were conducted within the astronaut's first two days of landing, were designed to test a person's vestibular system to see how well they maintain their post-flight balance.
The resolution on the MRI scans was variable: 10 astronauts had low-resolution scans and 17 had high-resolution scans. The pre-flight scans were collected anywhere from 18 to 627 days before the launch, and post-flight scans were collected between one and 20 days of landing.
The researchers also collected pre- and post-flight data on gray matter volume from the sensorimotor regions of interest. They analyzed volumes of the precentral, postcentral, and paracentral gyrus. They also compared changes in global tissue volume of gray matter, white matter, and cerebrospinal fluid, and looked for any significant changes in regional gray matter volume that were correlated with changes on the balance measurements taken pre- and post-flight.
According to Dr. Seidler, there were extensive volumetric gray matter decreases — between 5 and 10 percent — in the prefrontal and insula regions in the astronauts. She believes that the volume loss, which was even larger in those on the International Space Station, were due to fluid shifts during microgravity. There were also bilateral focal gray matter increases within the medial primary somatosensory and motor cortices, the areas that control movement and the processing of sensory feedback of the legs.
“Astronauts have to work to learn how to use their body in a microgravity environment,” said Dr. Seidler. “Every time we stand on Earth our leg muscles contract to counteract gravity. Obviously, this does not happen in space and the body has to learn new ways to respond.”
It is possible that the “small but localized gray matter increases we observed in sensorimotor brain regions parallel what has been reported in studies of neuroplasticity occurring with extended practice,” the scientists wrote in the paper. “Sensorimotor novelty and practice have been associated with positive brain plasticity and protection of neural tissue, particularly in sensorimotor brain regions in relation to spaceflight.”
The researchers did not observe significant pre- and post-flight changes in the precentral gyrus, postcentral gyrus, or vestibular cortex, a portion of the cerebrum which responds to input from the vestibular system (the location is not well defined, but some research indicates a right hemisphere dominance).
They also did not find significant changes in global gray matter, white matter, CSF, and total intracranial volume. The brain changes were also not correlated with the balance measurements.
The extensive information from the longitudinal astronaut study does not have any strong and reliable cognitive measures. Dr. Seidler's team is now collecting this data in the prospective study, which is designed to test the astronauts within three to five days of their return to Earth.
Understanding brain changes is critically important in the planning of future longer-term missions, said Dr. Seidler.
EXPERTS WEIGH IN
“This is a central paper, for sure,” said Jonathan 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. “The brain is one of the most rapidly adaptive systems. That we see anatomical changes and adaption comes as no surprise.”
There is a collection of symptoms called Earth Re-adaptation Syndrome, he explained. Astronauts are unsteady on their feet and uncoordinated, and they are not permitted to drive for a few weeks after landing because they look very much like a drunk driver. Dr. Clark said that they would fail a field sobriety test.
He noted that the changes in visual acuity and signs of intracranial hypertension have been a hot topic in space science since 2005. There have been 24 reports of astronauts with these symptoms. Some of these symptoms began years after their missions.
He said that findings from retrospective studies in general should not be over-interpreted. The prospective study underway will help answer important questions.
“It would be important to conduct functional imaging to see if physiological changes correlate with the anatomical changes,” said Dr. Clark. “If the anatomical changes don't correlate with anything than we really don't know what the changes mean.”
He said that many astronauts know about space stupids. They lose their intuition. They try to do something they have always done and their motor memory doesn't seem to work right.
Of course, the big question is how long do these brain effects last? “The nervous system is highly adaptive,” Dr. Clark explained. He and his colleagues have conducted a lot of animal studies in space. “Plasticity implies changes in synaptic function. We do see synaptic changes in certain parts of the brain. Animals have to relearn how to function in microgravity.”
“It's hard to draw conclusions about the brain changes in a retrospective study because astronauts undergo a lot of rigorous training before they are exposed to space flight,” said Stephen McGuire, MD, senior researcher for the United States Air Force, who studies the effects of high altitude on U2 pilots and runs the Hyperbaric Brain Injury Project for the Air Force.
“NASA shared MRI data with us and we see subcortical white matter changes that are similar with the findings in our U2 pilots. The caveat is that we don't know what the etiology is. Is it the experience, the radiation, or the hypobaric exposure?” Dr. McGuire asked.
The Air Force and NASA are now designing a study to answer some of these questions, he said.
EXPERTS: ON BRAIN CHANGES IN SPACE