Microgravity on a trip to Mars might leave astronauts emotionally impaired

A new study looking at mental function in volunteers taking part in a long-term simulation of microgravity has results that raise questions about impaired cognition and emotional function during long space voyages.

One of the many challenges with sending humans to Mars is the psychological stamina that will be required. A dangerous six-month voyage in a small spacecraft, with isolation far more extreme than that experienced by astronauts on the International Space Station, will create significant psychological and emotional strain.

And microgravity — when astronauts experience the feeling of weightlessness — may aggravate some of that strain by skewing astronauts' perception of the emotional state of their fellow travellers, according to the new study, published in the journal Frontiers in Physiology.

Skewed emotional perception in astronauts could create interpersonal stresses that could impair the efficiency of the astronaut team, according to the researchers.

"If we have someone in our workplace that we don't like, at least we can go home at night — we don't have to deal with that person," said Mathias Basner, a professor of psychiatry at the University of Pennsylvania School of Medicine.

That's a luxury astronauts on a long mission to Mars would not have, nor would they be able to seek help in a timely manner from mission support staff on Earth due to the distance causing a significant communication delay.

"If there's conflict among crew members, that really could affect the way they operate and actually endanger mission success in the long run," Basner said in an interview with Bob McDonald on CBC Radio's Quirks & Quarks.

Simulating microgravity on Earth

Basner led a team that tested the cognitive and emotional function of volunteers experiencing simulated microgravity. 

The simulation aimed to duplicate the physical alterations that happen to the brain in space

Without gravity pulling bodily fluids toward the ground, that fluid shifts toward the head, which is why the faces of astronauts returning to Earth after an extended stay on the space station often appear bloated.

Brain scans of astronauts newly returned to to Earth after long stays on the space station suggest that fluid shift also affects the brain.

"It has been shown that the brain is actually pushed to the top of the skull and compress[ed] there," said Basner.

"The thing is, though, we don't know what behavioural consequences these structural changes of the brain have." 

To simulate the upward fluid shift — and the relative inactivity of astronauts in microgravity — the researchers had 24 volunteers spend 60 days inactive in a bed with their heads tilted at a six-degree angle downward. 

They were then given comprehensive tests of cognitive function before, during and after the study.

New battery of cognitive tests

Basner said the standard battery of tests NASA currently uses to assess the cognitive performance of astronauts is relatively limited. There are five tests that predominantly focus on working memory, he says. 

He and his colleagues devised a more comprehensive set of tests to study a range of mental functions including sensory-motor speed, memory, abstract reasoning, reaction time, attention, flexibility of executive function, risk-taking behaviour and emotional recognition.

According to Basner, all of the test subjects showed an immediate slowing in their ability to perform the cognitive tasks during the microgravity simulation, and that slowness remained for the duration of the the study. 

"The one exception was the emotion recognition test," he said, which got significantly worse.

Impacts on emotional function

The researchers presented the test subjects with photographs of professional actors portraying different emotions — happy, sad, angry, fearful or neutral — with varying intensities.

The more time the study participants spent in the simulated microgravity condition, the slower their responses in the emotion recognition tests became.

"We also saw a tendency that with increasing time in bed rest, they would tend to pick more faces with negative valences, especially angry faces, and less faces that were happy or neutral," Basner said.

Control subjects who spent two months in bed rest but without the tilt, also showed a similar response in the emotion recognition tests, which complicated the results to some degree.

It's possible that different elements of the experimental condition — the fluid shift, the isolation, the immobility or even the orientation of the researchers' faces — contributed in different ways to the cognitive impairment. Basner hopes to disentangle these in future work. 

He also hopes to investigate whether artificial gravity countermeasures, like putting test subjects inside a spinning centrifuge to counteract the upward shift in bodily fluid, can protect against these impacts. Limited early trials of this strategy in this study haven't shown it to be effective.

Basner also cautions that individuals may respond to microgravity in different ways. His volunteers, for example, didn't receive any special training. The impact of microgravity on astronauts, who are rigorously trained and carefully selected for their mental and physical resilience, may be quite different.

Produced and written by Sonya Buyting