Putting astronauts on bed rest at a six-degree angle successfully simulates some of the physical effects of microgravity that are experienced in outer space. A new study found that over the course of two months in these conditions, it took more time for participants to pass a series of cognitive tests that probe abilities crucial in high-pressure situations such as space travel.
In a paper published Wednesday in Frontiers in Physiology, a group of researchers conducted a NASA-funded study that placed 24 "astronaut-like" healthy adults on strict bed rest for 60 consecutive days, with their bodies tilted head-down at a six-degree angle. It is the first study to investigate the effects on cognitive performance of a continuous and intermittent artificial gravity countermeasure during and after a head-down bed rest period.
Cognitive speed declined early on in the experiment, while accuracy on the tests was unaffected. Only speed on an emotion recognition test continued to decline with more days spent in bed rest, in which subjects increasingly identified facial expressions as angry and less as happy or neutral.
The research took place at the German Aerospace Center in Cologne, Germany. Mathias Basner, a professor in the Department of Psychiatry at the University of Pennsylvania and lead author of the paper, explained to The Academic Times that head-down bed rest is the standard way to simulate microgravity on earth because while there is still movement in space, astronauts encounter very little resistance or need for muscle use.
Without gravity, blood volume is redistributed in the human body and there is an upward fluid shift that also pushes the brain toward the top of the head. It's known that microgravity causes some structural changes to the brain, but any consequences or effects on cognitive performance in astronauts are not fully understood by scientists.
"Structural brain changes observed in astronauts after return from International Space Station missions have included an upward shift of the brain, changes in gray matter volume, increased white matter in the cerebellum, and cerebrospinal fluid volume increases in the third and lateral ventricle," the authors said in the paper.
The research team designed a series of cognitive tests for NASA tailored to astronauts, a job that generally requires them to be highly motivated and capable, Basner said. Beyond emotion recognition, the tests also measured things such as spatial orientation, risk decision making, sensorimotor speed, complex memory and abstract reasoning.
The participants were split into three groups of eight: one group experienced artificial gravity in a centrifuge for one 30-minute period every day, one group experienced artificial gravity for 30 minutes every day, spaced out in five-minute increments, and one group had no artificial gravity time for the duration of the experiment.
Basner and the researchers hypothesized that the two groups who experienced artificial gravity every day would perform better on the cognition tests than the control group, because the centrifuge rotated the astronauts enough so that their bodily fluid was redistributed from the head to the feet. However, they did not find this to be true.
"There was really no difference in cognitive performance between the three groups, suggesting that centrifugation of up to 30 minutes per day had no beneficial effects on the negative cognitive effects associated with head-down bed rest," Basner said. "Future studies will need to find out what was responsible for the changes in emotion recognition: the head-down bed rest, the relative isolation, or both."
Each subject had their own room, with no contact among the participants. Because they only had interaction with the research personnel for two months, Basner noted that the isolated conditions could have an impact on results. However, in space missions, it's also normal for astronauts to be isolated for long periods of time with only a few crew members.
All 10 tests and a brief alertness and mood survey were performed by participants multiple times before, during and after the head-down bed rest period. In the course of the experiment, the participants expressed several negative survey responses, and some of the responses further deteriorated during recovery. They reported feeling less healthy, and expressed higher levels of depression, boredom, loneliness and monotony.
The authors said this suggests a considerable psychological toll as a result of the experiment and "highlights the importance of adequate medical and psychological support during extended duration [head-down bed rest] studies."
The study's emotion recognition test showed the strongest results among the tests. It presented participants with faces showing different emotions, with instructions to identify the correct emotion. The participants displayed a tendency to choose negative emotions over positive or neutral emotions, and as the experiment progressed, they needed longer to make their choice.
Basner said this area of social performance is something that not many studies have measured in the past. And if astronauts struggle to decipher facial expressions, they could misread vital emotional cues from their fellow astronauts and compromise the safety of their mission.
"Sustained high levels of astronaut cognitive performance are of paramount importance for space mission success," the authors said in the paper. "Astronauts are exposed to several stressors related to living in an isolated, confined and extreme environment that can adversely affect cognitive performance, including microgravity."
Previous research using head-down bed rest has allowed subjects to lift up their head with pillows, while the rest of the body was still at a six-degree angle. But in order to properly analyze changes to the brain and cognitive performance, it's important that the head is also always in the six-degree head-down position, according to Basner, because in spaceflight, the physical conditions of microgravity are a constant stressor.
For future studies, the researchers recommended testing whether different modes or longer durations of centrifugation are more effective in reducing the effects of head-down bed rest on cognitive slowing, and also testing for varying levels of social isolation in a similar study design.
"Accuracy was unaffected during [head-down bed rest], both across domains and for the 10 individual cognition tests. This finding suggests that participants were able to maintain stable accuracy levels by slowing down," the authors said.
"In conclusion, 60 days of [head-down bed rest] were associated with moderate cognitive slowing and changes in emotion recognition performance, but these effects were not mitigated by either continuous or intermittent exposure to [artificial gravity] for 30 minutes daily," they said.
The study, "Continuous and Intermittent Artificial Gravity as a Countermeasure to the Cognitive Effects of 60 Days of Head-Down Tilt Bed Rest," published March 17 in the Frontiers in Physiology journal, was authored by Mathias Basner, David F. Dinges, Kia Howard, Tyler M. Moore, Ruben C. Gur, Alexander C. Stahn, the University of Pennsylvania; and Christian Mühl, the German Aerospace Center.