Understanding gravity’s brain effects key to human space success

Gravity is something we cannot see, feel or hear, but it affects every moment of our lives – and understanding it may be crucial to understanding human behaviour in space, and even on Earth, according to Dr Elisa Raffaella Ferrè, an experimental psychologist and cognitive neuroscientist at Birkbeck, University of London. Her laboratory combines psychological and space methods to research the effects of non-terrestrial gravity on cognition and behaviour.

Ferrè spoke about her team's work at The International Day of Human Spaceflight Conference, held at Birkbeck in April on the anniversary of Yuri Gagarin's first human flight to space. 

The effects of microgravity and changes in gravity on human cognition and behaviour is less well explored compared with research on the physical effects of space travel, but its effects can be profound. Results from a series of studies conducted by Ferrè's team suggest that being in microgravity can make humans worse at detecting pain, slower in performance and lead to poor decision-making.

A better understanding of gravity's effects on the human mind may be crucial as we may be on the cusp of a new era in space travel. This summer – should all go to plan – the first of NASA's Artemis missions will launch from Kennedy Space Center in Florida to fly to the Moon.

If the uncrewed Artemis I is successful, then Artemis II will carry four astronauts to lunar orbit in 2024, and then Artemis III will finally take humans back to the surface of the Moon – including the first woman and person of colour around 2025. Beyond this NASA has plans for a lunar outpost, the Lunar Gateway, to provide a permanent staging post for humans to visit the Moon and one day, Mars.

'We are currently entering a new era of human space exploration which will lead to deep space missions (Moon/Mars) on one side and space tourism on the other side,' Ferrè told me. 'Space agencies are planning to create sustainable lunar habitats and send the first people to Mars. Private space companies are competing to make space travel easier and more affordable. In my opinion this is a unique time for space exploration!'

She added: 'However, this "21st-Century Space Race" will present much greater challenges to human health and performance than the ones we have ever faced. Unprecedented distance, duration of missions, isolation and increasingly autonomous operations will be combined with prolonged exposure to non-terrestrial gravities.'

The human brain constantly processes and counteracts the effects of gravity, a 9.8 metres per second squared acceleration towards the ground on Earth, said Ferrè. It encodes this gravitational signal through the vestibular organ which is deep inside the temporal bone of the inner ear. It does this through small stones called otoliths which are aligned on a fluid surrounded by receptors. 'Every time that you move, this steering system is telling the brain the direction, the onset and the offset of the movement and the deceleration of the movement.'

When humans travel to space, our brains need to adapt to a different gravitational environment, 'and believe me things are complicated', said Ferrè.

That spaceflight and changes in gravity affect the health and physiology of space travellers is well-known. Brain changes from space travel are also documented. An MRI study of cosmonauts showed that the brain's insula – which contains the vestibular area – was reduced in size and connections to other brain areas after 200 days in space. Other studies show that the ventricles of the brain become larger with space travel because of shifting fluid in the body. Changes in brain structure are aligned with behavioural changes; some 60-70 per cent of astronauts suffer from Space Adaptation Syndrome, which is like extreme motion sickness, both during spaceflight and on returning to Earth. Fortunately, these brain changes revert to normal after weeks or months.

To examine the effects of gravity on behaviour and cognition, Ferrè and her team conducted a series of experiments to simulate space with a number of non-astronaut volunteers in the lab. Using a fingertip pain stimulus, they tested subjects for their pain thresholds first in an upright position – which is a proxy for normal Earth gravity, and then while they were in a 'head-down bedrest' position on a 3D tilting table with their heads six degrees lower than their feet to simulate the effects of microgravity in space.

'We found that when people were in head-down bedrest, they feel less pain. There's no reason to feel less pain… the poor people have an internal recalibration of pain perception.

The team got the same results when they used virtual reality to give subjects a visual perception of lower gravity. 'So if the visual information about gravity was not aligned with this internal model of gravity, we found that there was less pain perception,' she said.

When they tested people's response times in an auditory task under different gravity environments using the head-down bed rest method and the VR technique, the team found that they were slower in microgravity.

They also looked at people's decision-making abilities under different gravity environments using a random number generating task. Ferrè said the brain's frontal area is involved in generating random numbers and this is also involved in executive function and decision-making. So they used this as an indirect way to assess people's decision-making performance. People in the upright position were much better at generating random numbers than those in a head-down bedrest position who were 'suboptimal in taking decisions'. 'They were sticking with the same number over and over again, which indicates very poor decision making,' said Ferrè.

Overall their results might indicate how tricky the effects of gravity changes in space travel might be. 'Think about these astronauts on the Moon or Mars. They feel less pain, they are slower, they might have poor decision-making and also they are happy to take risks. This is not really an ideal scenario!' said Ferrè.

On a different note, she pointed out: 'What it shows us is that perhaps terrestrial gravity which is has been largely neglected in psychology and neuroscience might actually be very important for our behaviour here on Earth. In Psychology, you have this bias that if you cannot see it, feel it, or hear it doesn't matter. But actually gravity that you cannot feel it, see it, or hear it, might be an absolute reference for behaviour, something that helps us interact with the environment every day.'