Astronauts aboard the International Space Station (ISS) had reduced memory, attention and processing speed after six months, raising concerns about the impact of cognitive impairment on future space missions to Mars.

The extreme environment of space, with reduced gravity, harsh radiation and the lack of regular sunrises and sunsets, can have dramatic effects on astronaut health, from muscle loss to an increased risk of heart disease. However, the cognitive effects of long-term space travel are less well documented.

Now, at NASA’s Johnson Space Center in Houston, Texas, and her colleagues have looked at the cognitive performance of 25 astronauts during their time on the ISS.

The team put the astronauts through the same set of 10 tests both on Earth and on the ISS. These were repeated once before, twice during and twice after the mission, within 10 and 30 days of landing. These tests measured certain cognitive capacities, such as finding patterns on a grid to test abstract reasoning or choosing when to stop an inflating balloon before it pops to test risk-taking.

The researchers found that the astronauts took longer to complete tests measuring processing speed, working memory and attention on the ISS than on Earth, but they were just as accurate. While there was no overall cognitive impairment or lasting effect on the astronauts’ abilities, some of the measures, like processing speed, took longer to return to normal after they came back to Earth.

Having clear data on the cognitive effects of space travel will be crucial for future human spaceflight, says at Birkbeck, University of London, but it will be important to collect more data, both on Earth and in space, before we know the full picture.

Free newsletter

Sign up to Launchpad

Sign up to newsletter

“A mission to Mars is not only longer in terms of time, but also in terms of autonomy,” says Ferrù. “People there will have a completely different interaction with ground control because of distance and delays in communication, so they will need to be fully autonomous in taking decisions, so human performance is going to be key. You definitely don’t want to have astronauts on Mars with slow reaction time, in terms of attention-related tasks or memory or processing speed.”

It isn’t surprising that there were some specific decreases in cognitive performance given the unusual environment of space, says at the University of East Anglia in Norwich, UK. “It’s not necessarily a great cause for an alarm, but it’s something that’s useful to be aware of, especially so that you know your limits when you’re in these extreme environments,” she says.

That awareness could be especially helpful for astronauts on longer missions, adds Bower. “It’s not just how you do in those tests, but also what your perception of your ability is,” she says. “We know, for example, if you’re sleep deprived, that quite often your performance will decline, but you won’t realise your performance has declined.”

More light could be shed on how space flight affects astronauts’ health after the creation of the first “space-omics” biobank – a collection of thousands of blood and tissue samples, plus medical information, taken over multiple space missions.

These include missions to the International Space Station, as well as the first all-civilian space flight, SpaceX’s Inspiration4, which took four non-government-trained astronauts into space for three days in 2021.

Called the Space Omics and Medical Atlas (SOMA), the resource contains detailed medical data, such as on DNA damage and changes in people’s gene activity and immune system functioning, collectively known as biomarkers.

Space flight is known to pose certain health risks. For instance, astronauts lose bone density and muscle mass due to the lack of gravity, and higher levels of radiation in space seem to cause cell and DNA damage, which have a range of impacts on the body. These effects may be why in later life and after being in space.

Collecting astronauts’ medical data in a consistent way via the SOMA biobank will help researchers understand more about these changes and potentially develop ways to mitigate them, says at Weill Cornell Medicine in New York, who helped put the biobank together.

“Biomarkers don’t always translate into anything that’s clinically meaningful, but it’s a nice way to start to understand how this unique environment is impacting us,” says at the University of South Wales in the UK, who wasn’t involved in the work.

Free newsletter

Sign up to Health Check

Sign up to newsletter

One insight from the Inspiration4 mission is that, despite the astronauts experiencing a host of biomarker changes, most measurements returned to normal within a few months of them coming back to Earth.

This suggests that sending civilians into space doesn’t pose more health risks than sending professional astronauts, says Mason. “Instead of people training for decades to go, we could start to really open up space towards more and more people.”

The results from Inspiration4, which was crewed by two men and two women, also suggest that the changes in gene activity returned to normal faster in the women. That may be because women’s bodies have to be able to cope with a potential pregnancy, says Mason. “Being able to tolerate large changes in physiology and fluid dynamics may be great for being able to manage pregnancy, but also manage the stress of spaceflight.”

at the University of Exeter in the UK says it will be helpful for researchers around the world to have a common resource they can use. “You need to have a consistent approach to collecting samples,” he says.

at King’s College London says understanding the health impacts of space flight will become more important if longer missions happen, such as journeys to Mars. “Anything that leads to extended duration missions, it’s more important to know what’s going on and, ideally, address it,” he says.