Should humans venture to Mars, they'll need some serious brain protection.
Exposure to radiation similar to the galactic cosmic rays of outer space drastically prunes mice's brain cells, a new study finds. As a result, irradiated mice performed worse on certain behavioral tests, compared to un-irradiated ones. "This is going to be a concern for NASA," says Charles Limoli, a radiation oncologist at the University of California-Irvine who was the study's senior scientist. "I would expect the very same thing to occur in the human brain. Their brains aren't that different in terms of response to radiation."
Limoli's study is one of several aimed at divining the neurological consequences of sending people to space for longer periods of time. It's part of an overall science portfolio at NASA that's supposed to help the agency assess the risks of long outer-space missions.
The science will be relevant should the agency — or others — send astronauts to Mars in the future. A trip to the Red Planet would expose people to more space radiation than anything humankind has faced. Voyages to the moon lasted only days; it would take months to get to Mars. American astronauts have spent months aboard the International Space Station, and one will soon spend a year there, but the ISS flies below the Earth's magnetosphere, which shields it from most cosmic rays.
For their study, Limoli and his colleagues sent a beam of charged particles, representative of what an astronaut might experience during a 10- to 30-day mission, at young adult mice. Six weeks later, the researchers tested the mice. Compared to mice who had not been exposed to charged particles, the exposed mice performed more poorly on tests that required them to notice when researchers moved the toys in their cage, or when new toys replaced the old ones. Two weeks after that, the scientists dissected the mice, examined the prefrontal cortex region of their brains, and found many of the branches in the mice's brain cells there were missing. Such branches are important for brain cells to communicate with one another.
While it's reasonable to think such brain-cell pruning would happen to human brains exposed to galactic cosmic rays, it's unclear how that would affect a human's behavior. It's not expected to be life-threatening, Limoli says, but it might affect people's ability to react to new situations.
How can NASA prevent that in astronauts? Covering a spaceship with adequate shielding material would make the ship too heavy, experts say. So Limoli is working on studies of drugs that could protect his mice's brains from radiation, with the hopes that they will one day work for people too.
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