Scientists document how space travel messes with the human brain

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Many people are excited when they hear about the accomplishments of astronauts. Some envy their short-term missions aboard the space shuttle or the long-term missions aboard the International Space Station (ISS). But it's not all fun and excitement. Living in an environment of reduced gravity (microgravity) conditions can put a strain on the human body, including the brain. A recent study by NASA showed that fluid inside the brain expands during long missions, and that can be a problem.

The brain is an organ weighing about 3 pounds (1.3-1.4 kg) in adults. It is protected by the skull bones, but it is also cushioned by liquid inside and outside. This fluid also travels down the spinal cord, so it is known as cerebrospinal fluid. You can see it in blue in the picture below.

Cross-section images of brain with cerebrospinal fluid

(from Wikipedia and thoughtco.com)

Like blood, this fluid actually moves (see the black arrows on the left image above) from the center of the brain, where it is made, to a lining around the brain, down the spinal cord, and back again. There is no pump like the heart. Cells in the center cavity have little hair outside them that paddle the liquid. The cavities in the center of the brain that have the greatest volume are called ventricles (just like the 2 ventricles in the heart). There's about half to two-thirds of a cup (125-150 mL) in your body at any moment, and it gets absorbed by the body, so the brain makes about 2 cups (500 mL) per day.

You can see the beating pulses of the fluid in this MRI. 

Video courtesy of © Nevit Dilmen, CC BY-SA 3.0

https://commons.wikimedia.org/w/index.php?curid=9388427

One of the main functions of this fluid is to be a cushion against the brain shaking inside the skull. There is also a barrier layer of cells (membrane) between the fluid and blood flow that protects the brain from infection.

On Earth, gravity pulls down on the body and everything inside. In orbit or beyond, the reduced gravity no longer does that, so your blood and other fluids are more evenly distributed. That makes a weightless astronaut's face look puffy. A similar thing happens to the mucous membranes in the nose, and it makes the astronaut sound like they have a head cold. Both of these tend to go away after a few weeks as the body adjusts to microgravity conditions.

Puffy face on right while in space (photo from SpaceRef.com)

 So, in a similar way, the brain's ventricles are no longer under gravity pressure, so they swell up, at least for the first 6 months of being in space. The graph below for one of the brain's ventricles shows the difference between a 2-week flight and flights of 6 months or a year. The actual amount of swelling is small (0.15 mL or 0.03 teaspoon in the third ventricle, 0.75 mL or 0.15 teaspoon in the right lateral ventricle). But these were still statistically confirmed. They amount to a 10-13% increase.

Swelling in 2 brain ventricles depending on the length of the flight (from Nature.com)

Also, the more missions the astronauts went on had an influence on this expansion. If they went on fewer missions, the expansion was less (see graph below).

Data from Nature.com

If astronauts went back into space within 3 years, the expansion was minimal. After a 3-year delay, though, the body doesn't remember how to compensate, so they expand again by about 10-20%. 

A key point in this research is that scientists have not determined whether this expansion is a problem to brain functions during space flight. Earlier studies in 2011 and 2019 , though, have shown that 29% of astronauts on short-term flights and 60% of the on long-term missions suffered vision problems which might be related to pressure increases in the brain. 

For more information on other changes to the human body in space, see this Space.com article.