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Any astronauts traveling to Mars would not only have to endure considerable psychological stress but also exposure to radiation lasting hundreds of days, which could cause brain impairments. A new study that exposed mice to the kind of radiation levels seen in deep space found that the rodents displayed learning and memory issues, as well as anxiety.

Your brain on space radiation

On August 1912, Austrian physicist Victor Hess made a historic balloon flight that opened a new window of understanding of the universe. As he ascended to 5,300 meters (17,400 ft.), he measured the rate of ionization in the atmosphere and found that it increased to nearly three times that at sea level. He concluded that radiation was penetrating the atmosphere from above. What Hess had discovered were cosmic rays.

Galactic cosmic rays can be found everywhere in the universe. They’re the remnants of supernovae – exploding dying stars, which release huge amounts of energy. Luckily, the Earth’s atmosphere acts as a shield against them. However, in outer space, it’s all free to roam and wreak havoc on life.

Deep space exposure to radiation has concerned scientists for a long time. Although humans have yet to travel beyond the moon, manned missions to Mars have been considered for decades so this is not the first time researchers have investigated the effects of radiation on biological systems traveling through space. And the results so far haven’t been encouraging at all.

A 2015 study exposed mice to radiation similar to the cosmic rays that permeate space and found the animals experienced declines in cognition and changes in the structure and integrity of brain nerve cells and synapses (where nerve impulses are sent and received). The mice became easily confused and lost their tendency to explore new environments. According to scientists at the University of California, Irvine, exposure to cosmic rays could lead to long-term brain damage, resulting in cognitive impairment and even full-blown dementia. 

In a new study published in the journal eNeuro, the researchers at the University of California, Irvine repeated their radiation exposure experiments on mice, only this time they used space relevant dose rates (1mGy/day) over a long period (6 months). Previous studies used short busrts of exposure with a higher dose of radiation. The cumulative radiation exposure is technically the same but using a longer dosing regiment is much closer to reflecting real deep space conditions.

Six months after the male mice in the study received their first radiation dose, the researchers found that signaling between neurons in the prefrontal cortex (the seat of higher-order cognition) and hippocampus (involved in memory) was impaired. What’s more, the mice also displayed anxiety, which suggests the radiation may have also affected the amygdala.

The effects were similar to those reported by past studies using dose rates that were about 400 times higher.

According to the researchers, 1 in 5 astronauts on a deep space mission would likely suffer from anxiety; 1 in 3 would be likely to deal with memory issues; and all of them may struggle to make new decisions.

Bearing all of this in mind, if the changes seen in the mice occur in astronauts, it’s likely that space radiation exposure may compromise their ability to problem solve and respond to new situations. This can result in potentially dangerous situations since communications between the Mars-bound spacecraft and Earth could be delayed by up to 20 minutes.

However, Charlies Limoli, the study’s lead author and a professor of radiation oncology at UC Irvine, says that the findings shouldn’t discourage manned deep space mission. He argues that — while radiation represents one of the biggest problems we will face in deep space travel — it would have been more concerning if we weren’t aware of the adverse effects astronauts might face.

At the moment, NASA and other groups are working on advanced shielding and drugs that might control the effects of cosmic rays.