Astronaut Bruce McCandless II, mission specialist, participates in an extra-vehicular activity (EVA), a few metres away from the cabin of Space Shuttle Challenger. He is using a nitrogen-propelled hand-controlled Manned Maneuvering Unit (MMU). He is performing this EVA without being tethered to the shuttle. The picture shows a cloud view of the Earth in the background. Taken on 11 February 1984. NASA, Public domain, via Wikimedia Commons.

Astronauts’ processing speed, working memory and attention slowed down, but a few months in space did not result in lasting cognitive impairment.

A stay in space exerts extreme pressures on the human body. Astronauts’ bodies and brains are impacted by radiation, altered gravity, challenging working conditions, and sleep loss – all of which could compromise cognitive functioning.

At the same time, they are required to perform complex tasks, and minor mistakes can have devastating consequences.

Little is known, however, about whether astronauts’ cognitive performance changes while in space.

Now, working with 25 astronauts who spent an average of six months on the International Space Station (ISS), researchers in the US have examined changes in a wide range of cognitive performance domains.

This dataset makes up the largest sample of cognitive performance data from professional astronauts published to date.

First author of the study, Dr Sheena Dev, a researcher at NASA’s Behavioral Health and Performance Laboratory, said: “We show that there is no evidence of any significant cognitive impairment or neurodegenerative decline in astronauts spending six months on the ISS.

“Living and working in space was not associated with widespread cognitive impairment that would be suggestive of significant brain damage.”

Slower, but no less accurate

Astronauts underwent a series of tests developed to assess a range of cognitive domains using ten subtests.

For each of these tests, the researchers measured speed and accuracy at five time points: pre-mission, early and late flight respectively, as well as at ten and thirty days after landing.

The results showed that responses to tasks assessing processing speed, working memory, and attention were slower than on Earth, but they were no less accurate. These changes, however, did not persist equally long.

Dev observed: “Slowed performance on attention, for example, was only observed early during the mission while slowed performance on processing speed did not return to baseline levels until after the mission ended and crew were back on Earth.”

Overall, astronauts’ cognitive performance was stable, and the researchers did not find evidence that would suggest damage to the central nervous system during a six-month space mission.

Data for future space missions

The results showed that some cognitive domains were more susceptible to be impacted than others.

Dev said: “Even on Earth, processing speed, working memory, and attention are cognitive domains that can show temporary changes when an individual is under stress. Other domains, such as memory, are less vulnerable to stressors.

“For example, if you happen to have a really busy day but couldn’t get much sleep the night before, you might feel like it’s hard to pay attention or that you need more time to complete tasks.”

Astronauts are exposed to these stressors, too, but additional stressors that are unique to space also take their toll.

Dev advised: “We found that the most vulnerable domains while astronauts are aboard the ISS are the same as those that are more susceptible to stressors on Earth.” 

The researchers said that their study can help them understand which changes in cognitive performance might be expected when humans go to extreme environments.

What the study didn’t show, however, is why those changes happened, the researchers cautioned. It also didn’t set out to assess whether astronauts’ operational performance suffered.

Dev said: “It could be that even in areas with observed declines, astronauts were still able to compensate and effectively complete their tasks.”

Once astronauts start travelling deeper into space – to the moon or Mars, for example – this data from the low Earth orbit can also provide a comparison which can help detect cognitive changes brought about by increased radiation exposure and extended communication delays more quickly, the researchers concluded.

The study is published in Frontiers in Physiology.