Mission to Mars may warp astronaut brains

NASA’s Opportunity Mars rover captured this mosaic of the dusty Martian landscape, with its tracks visible to the right. Image courtesy of NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

One day, space explorers might stroll along the red rocks of Mars. But radiation exposure during the trip may wipe away their memories of home.

A new report says that cosmic rays can change the physical architecture of the mind’s nerves, harming the brain regions that govern memory.

Cosmic rays, comprised of high-speed atomic particles, blanket the Milky Way galaxy. The radiation constantly bombards our planet, but the Earth’s magnetic field and its atmosphere save us from the most dangerous rays.

People who venture into deep space aren’t so lucky, as cosmic rays can easily penetrate a spaceship’s metallic hull or a space helmet. So before NASA sends anyone into deep space, they want to figure out the possible long-term ramifications of exposure to cosmic radiation.

One item of concern is radiation-induced memory loss, says cancer researcher Charles Limoli of the University of California Irvine, who led the report published May 1 in Science Advances. Cancer radiotherapy can impair human memory and spawn dementia, which is what drew Limoli’s team to the research.

“Upon penetrating the body, these charged particles leave tracks of damage on the same scale as neurons,” Limoli said. “So we reasoned that [cosmic] irradiation might elicit long lasting structural changes in neurons that would lead to cognitive impairment.”

Digitally reconstructed images of rodent frontal lobes have more nerve branches (green lines) and connections (red dots) without “cosmic” radiation exposure (left panel). Image courtesy of Science Advances.

To test this idea, Limoli’s team exposed mice to short bursts of high-energy particles, and then six weeks later, checked the rodent’s ability to remember the locations of toys. Rodents exposed to radiation wandered aimlessly, losing their ability to distinguish between old toys and newer ones placed in an arena.

Limoli’s team wanted to know why, so they looked closer at the nerve cells inside the frontal lobes that interact with other parts of the brain to create memories. They found that cosmic rays melted nerve endings, known as dendritic spines.

“The reductions in spine density disrupted neurotransmission and correlated with cognitive decline,” says Limoli.

Prior work on cosmic rays generated a similar drop in the mental prowess of rodents, but many of those studies used radiation levels that are three to four times higher than what is typically detected in deep space, said astrobiologist Peter Guida of Brookhaven National Laboratory. “But [Limoli’s] study used ‘space relevant’ doses of charged particle radiation.”

Many questions remain. Will these trends apply to humans? And if they do, how will NASA protect astronauts?

Some scientists recommend using heavy-duty plastics or building generators that can recreate the magnetic fields found on Earth. Arguably, the wildest suggestion is using poop as a cosmic ray shield.

But for now, NASA has asked Limoli to lead a nationwide, $9 million effort to look into how cosmic radiation might affects astronauts’ cognition.

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