Long-term deep space missions may alter brain proteins in astronauts, and cause cognitive deficits like lapses in attention and slower reaction times.

Scientists at the Johns Hopkins University report that rats exposed to high-energy particles, simulating conditions astronauts would face on a long-term deep space mission, show lapses in attention and slower reaction times, even when the radiation exposure is in extremely low dose ranges.

The cognitive impairments — which affected a large subset, but far from all, of the animals — appear to be linked to protein changes in the brain, the scientists said.

The findings, if found to hold true in humans, suggest it may be possible to develop a biological marker to predict sensitivity to radiation’s effects on the human brain before deployment to deep space.

When astronauts are outside of the Earth’s magnetic field, spaceships provide only limited shielding from radiation exposure, said study leader Robert D Hienz.

If they take space walks or work outside their vehicles, they will be exposed to the full effects of radiation from solar flares and intergalactic cosmic rays, he said, and since neither the Moon nor Mars have a planet-wide magnetic field, astronauts will be exposed to relatively high radiation levels, even when they land on these surfaces.

But not everyone will be affected the same way, the experiments suggest.

“In our radiated rats, we found that 40 to 45 per cent had these attention-related deficits, while the rest were seemingly unaffected,” Hienz said.

To conduct the new study, rats’ heads were exposed to varying levels of radiation that astronauts would normally receive during long-duration missions, while other rats were given sham exposures.

They were tested every day for 250 days. The radiation-sensitive animals (19 of 46) all showed evidence of impairment that began at 50 to 60 days post-exposure and remained through the end of the study.

Lapses in attention occurred in 64 per cent of the sensitive animals, elevations in impulsive responding occurred in 45 per cent and slower reaction times occurred in 27 per cent.

The impairments were not dependent on radiation dose.

Additionally, some of the rats didn’t recover at all from their deficits over time, while others showed some recovery over time.

The radiation-sensitive rats that received higher doses of radiation had a higher concentration of transporters for the neurotransmitter dopamine, which plays a role in vigilance and attention, said Catherine M Davis, the study’s first author.

The study was published in the journal Radiation Research.

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