Spending extended time in space wreaks havoc on the body. You lose bone density. Your muscles waste away. And according to a new study published Monday in the journal Scientific Reports, you also may get "space brain," a form of brain damage caused by galactic cosmic ray radiation — and it could be a barrier in the pursuit of colonizing Mars.
In a preclinical rodent study performed by Charles Limoli and his team at the University of California, Irvine, researchers found that radiation exposure equivalent to the radiation experienced in space caused long-term brain damage to rodents, leaving them with cognitive impairment and dementia.
Most surprising, Limoli said, was how persistent the damage to the animals' cells actually was. "In most cells there's a level of recovery," he said on a phone call Monday. "We followed up six weeks, 24 weeks later. The changes don't resolve."
The more time you spend in space, the more you're exposed to space radiation. Since Limoli's findings indicate irreparable damage from long-term exposure, that 300-day trip to Mars could mean serious trouble for human brains.
Permanent cognitive impairment comes with an alarming side effect: the loss of "fear extinction," a tool the brain uses to suppress traumatic events.
"It's like if you hear a car horn and you associate that with an oncoming car — that's a problem in a crosswalk," Limoli said. "But if you hear it in your house, [fear extinction] will cause you to freak out because you can't dissociate that the car isn't in your living room."
In other words, the irradiated rodents couldn't unlearn stressful associations, which could pose a major problem for astronauts who need to occasionally perform tasks under pressure — or worse, galactic travelers who've experienced traumatic life events.
About 7.8% of people will experience post traumatic stress disorder in their lifetimes. And according to Limoli, "If you superimpose a bunch of stress with irradiation, I can't see that being beneficial."
"Space brain" doesn't pose an insurmountable roadblock to colonizing space, just a hurdle that needs to be addressed beyond rodents in Limoli's lab.
Unfortunately, that's complicated: Limoli can't just test the cognitive impact of radiation on former astronauts, because no astronauts have gone to the surface of Mars. Even astronauts on the International Space Station are still protected by the Earth's magnetosphere, so the radiation isn't as destructive. According to Limoli, the only humans who might have experienced equivalent radiation are the astronauts who went to the moon — and that's a very small sample size.
For now, Limoli advocates for improved research into spacecraft shielding, better astronaut helmets and pharmacological solutions for protecting the neural pathway transmissions that degrade with radiation exposure. It's going to take a while — we are, after all, still in the shooting-radiation-at-rats phase. But the slow road is necessary. Because before we can put people on the surface of the red planet, we need to protect their brains.
"Hundreds of thousands of years from now, if we want deep space travel, and we have to propagate life for generation after generation, you have to come up with a solution to this," Limoli said. "But that's part of the challenge, part of the fun. We're not going to solve this in a year, but once we understand this and throw money at the problem, we'll make significant inroads to understanding it."