Hanging Out in Space Deforms Brain Tissue, New Cosmonaut Study Suggests

While gray matter shrinks, cerebrospinal fluid increases. What’s more: These changes do not completely resolve once back on Earth.

Russian cosmonaut Fyodor Yurchikhin on a spacewalk in 2013, completing maintenance on International Space Station. NASA

Researchers are increasingly finding that spending extended periods in space has complicated effects on the human body. Exposure to space radiation is a big concern for long-term astronauts. Life in zero-G could lead to cardiovascular issues and bone loss. Living in enclosed spaces or habitats could also lead to weakened immune systems and the spread of disease. Space can even affect which genes are expressed. Now, reports Maya Wei-Haas at National Geographic, we can add another symptom to the list: deformed brain tissue.

In a new study published in the New England Journal of Medicine, an international team of researchers examined MRI images of the brains of 10 Russian cosmonauts before and after they spent extended periods on the International Space Station and then again seven months later for seven of the men. On average, the cosmonauts—all men in their mid-forties—each spent 189 days in the station, experiencing microgravity.

According to the study, what they found is that changes took place in three different brain tissues. After the space flight, the amount of gray matter—which makes up much of the cortex, or surface of the brain—was reduced, with an area called the right middle temporal gyrus seeing the most shrinkage at 3.3 percent. The amount of cerebrospinal fluid, which fills up cavities inside and outside the brain, had increased in volume, maxing out with a 12.9 percent increase in the third ventricle. The white matter—which is primarily bundles of nerves that send signals around the brain and to the spinal cord—appeared unchanged.

The follow up images months later showed that the amount of gray matter rebounded, but was still less than baseline measurements. The amount of cerebrospinal fluid continued to increase, indicating that the cerebrospinal fluid circulation system in the cosmonauts was impacted long after they returned to Earth. The white matter appeared to decrease in volume over the same time. The researchers hypothesize that this is also because of the cerebrospinal fluid. As the fluid swelled inside the brain during space flight, it forced water into the white matter, increasing the volume of white matter. Once back under normal gravity conditions, the water in the white matter was released, appearing to shrink.

It’s possible the changes may be permanent, or given enough time if the brain would return to normal. But the study indicates that space brain is a real phenomenon.

“Taken together, our results point to prolonged changes in the pattern of cerebrospinal fluid circulation over a period of at least seven months following the return to Earth,” co-author Peter zu Eulenburg, a neurologist at Ludwig-Maximilians-Universität München, says in a press release. “However, whether or not the extensive alterations shown in the grey and the white matter lead to any changes in cognition remains unclear at present.”

Cerebrospinal fluid has been on the astro-medicine radar screen for a while. One complaint long-term astronauts often have after their time in orbit is blurred vision, which sometimes resolves itself but is sometimes permanent. Mark Strauss at National Geographic reports that in 2016 researchers also looked at the cerebrospinal fluid volumes of seven astronauts who had spent time in orbit, finding that the volume of fluid—which helps keep a steady pressure in the brain—increased as a result of the microgravity. All that extra fluid pushed against the back of the eyes, flatting them and inflaming the optic nerve.

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