Cognitive problems could result from long space missions in zero gravity
With long space missions a real prospect in the near future, scientists are trying to find novel ways to mitigate the negative impacts of reduced gravity on the human body. A compelling new study led by a team from the University of Pennsylvania is suggesting microgravity can negatively affect cognitive performance, and brief exposures to artificial gravity unfortunately do not mitigate the problem.
Current plans for a crewed return mission to Mars mean it is vital we understand what happens to a human brain when it's subjected to reduced gravity for several years. A growing body of research is indicating extended periods of time in space can cause significant changes to an astronaut's brain.
Studies looking at the physiological effects of space on astronauts following stays of several months on the International Space Station (ISS) have revealed significant changes to white and gray matter. These changes can cause blurry vision or even influence an astronaut’s ability to walk properly. But perhaps of greatest concern is how these neurophysiological changes can influence cognition and behavior.
In the absence of Earth’s gravity fluid in the body tends to rise upwards. This can lead to innocuous swelling of the face, but more concerning cognitive issues such as disorientation and slowing of response times can also result.
For around half a century scientists on Earth have deployed a novel method to investigate the physiological effect of microgravity. Called head-down bed rest (HDBR), the technique essentially has participants lie down at a slight six-degree angle for extended periods of time.
This new HDBR study recruited 24 subjects for a long 60-day project. As well as investigating the neurological effects across a range of cognitive performance domains, the research was looking to find out whether temporary blasts of artificial gravity could mitigate any deleterious effects.
“Participants regularly completed 10 cognitive tests relevant to spaceflight that were specifically designed for astronauts, such as spatial orientation, memory, risk taking and emotion recognition,” explains Mathias Basner, one of the researchers working on the project. “The main goal was to find out whether artificial gravity for 30 minutes each day – either continuously or in six 5-minute bouts – could prevent the negative consequences caused by decreased mobility and head-ward movement of body fluids that are inherent to microgravity experienced in spaceflight.”
The cohort was split into three groups. One group, the control, simply spent the entire 60 days in the HDBR position. The other two groups spent stretches each day spinning in a centrifuge simulating the effect of artificial gravity.
Alexander Stahn, another author on the new study, says this centrifuge test was designed to replicate the most cost-effective way artificial gravity could be deployed in a spacecraft scenario.
“There are two ways to produce gravity in spaceflight: rotate the whole spacecraft/station, which is expensive, or just rotate the astronaut,” explains Stahn. “The centrifuge could be self-powered, doubling up as an opportunity for exercise.”
The cognitive results revealed all three groups displayed a “modest but statistically significant slowing across a range of cognitive domains.” Most cognitive changes were seen relatively early in the two-month study period and increasing time did not seem to induce greater changes.
The one factor the researchers did note as significantly decreasing over a longer period of time was emotion recognition performance. Here, the subjects were asked to identify emotion in facial images. As time passed the subjects increasingly identified faces as angry.
The researchers are cautious to jump to any conclusions regarding this finding, suggesting further work will be necessary to unpack whether these deficits in emotional processing were a direct result of the HDBR process, or a result of the nature of the study itself (low levels of human interaction, etc).
Cognitive neuroscientist Elisa Raffaella Ferre, who did not work on this new research, suggests this possible disruption to emotion identification is a vitally important finding that should influence future investigations.
“The ability of astronauts to be sharp and quick thinkers is crucial to a space mission,” writes Ferre in The Conversation. “So is the capability to correctly “read” each other’s emotional expressions, given they have to spend a lot of time cooped up together in a small space. Space agencies should therefore consider adequate pre-flight psychological training as well as in-flight psychological support in order to minimize this risk.”
Perhaps the most concerning finding is no differences were seen across all cognitive performance and subjective measures between the control group and the two groups tested under artificial gravity conditions. Stahn suggests further tests are planned to find out whether alternative countermeasures can mitigate some of the negative effects.
“Unfortunately, we found that the artificial gravity countermeasures in our study did not have the desired benefits,” says Stahn. “We are currently performing additional analyses using functional brain imaging to identify the neural basis of the effects observed in the present study.”
It will be challenging to truly understand the physiological, psychological and cognitive effects of space travel until we actually send a craft with humans on the long journey to Mars and back. These kinds of simulation studies can, however, offer scientists vital insights into what problems we need to look out for and how we can mitigate these negative potentialities.
“Astronauts on long space missions, very much like our research participants, will spend extended durations in microgravity, confined to a small space with few other astronauts,” says Basner. “NASA’s current plans for a return mission to Mars lasts approximately 1,000 days, and the astronauts’ ability to correctly ‘read’ each other’s emotional expressions will be of paramount importance for effective teamwork and mission success.”
The new study was published in the journal frontiers in Physiology.