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Time spent in zero G changes the body: Astronauts come home with bone loss and muscle weakness. But what happens in their heads? To find out, researchers examined MRI’s of astronauts’ brains taken before and after flight. They looked at 12 astronauts who spent two weeks on the shuttle crew and 14 who spent half a year on the International Space Station.

What they saw is that the spacefarers’ gray matter appeared compressed…particularly around the front and sides of the brain and the area around the eyes. That’s probably due to a redistribution of cerebrospinal fluid, which is no longer being pulled down by gravity, the researchers say. 

The exception to this compression is in a small area of the brain that controls the feeling in, and movement of, the legs. This region expanded in the astronauts—particularly the ones who spent six months circling the earth. That change, the researchers say, could reflect the formation of new neural¹ connections as the brain tries to adapt to the weightless conditions. The study is in the Nature partner journal Microgravity. [Vincent Koppelmans et al., Brain structural² plasticity with spaceflight]

The findings could have applications back here on terra firma. For example, we could learn more about treating the brain changes that take place in people who are on extended bedrest, with their feet elevated and thus higher than their heads.

The brain change is yet another thing that future space travelers, like those that may someday head to Mars, should keep in mind. No matter what size that mind may be.

—Karen Hopkin