NASA Put Mice in Space and They Started Behaving in an Unusual Way

space mice
A mouse that was part of the experiment on the International Space Station. April Ronca et al.

Scientists have discovered that when sent to space, mice engage in an unusual behavior where they started doing laps of their cage in a "coordinated group activity."

The mice were sent to the International Space Station in the NASA Rodent Habitat. This experiment, led by April Ronca, of the NASA Ames Research Center, was to study how their behavior might change during a long duration spaceflight.

With NASA currently working out ways to send humans to Mars, understanding how astronauts might react to spending long periods of time in space is hugely important. Studies have already shown that physiological changes take place in animals. However, there has been less focus on how behaviors might change as a result of the space environment.

In a study published in Scientific Reports, Ronca and colleagues describe how they sent two groups of female mice to the ISS—one group was 16 weeks old, the other 32 weeks. These were compared to a control group on Earth.

The space mice were kept on board for between 17 and 18 days—this would be equivalent to a human on a long duration spaceflight. The mice were recorded so researchers could analyze their behavior.

Over the course of the experiment, the team found the space mice partook in "species-typical behaviors." They followed circadian cycles and were as physically active as on Earth.

However, after seven to 10 days, the younger group of mice started displaying a "unique circling or 'race-tracking' behavior" where they whizzed around the cage at speed. Initially, they moved their bodies along a "ovular trajectory," and "propelling themselves by pushing off walls with hindlimbs," the scientists wrote. "This behavior quickly evolved into full circular laps."

A few days later, multiple mice started circling the cage in this way at the same time—the behavior, they say, evolved into a "coordinated group activity."

They wrote: "The entire progression from individual single circles to group multi-circling behavior developed in both NASA Validation cohorts over just three days… Circling participation and lap rate (began abruptly, then gradually increased to high levels maintained over the remainder of the mission."

This "organized group circling" behavior, the team says, is unique to mice in space and could have a number of explanations. It could be that the mice are rewarded by the effect of physical exercise, or that they like the sensation of self-motion. However, they say more research will be required to understand why the mice started behaving this way.

Martha Hotz Vitaterna, Executive Director, Center for Sleep & Circadian Biology at Northwestern University, has previously studied mice in space but was not involved in this research. Commenting on the study, she told Newsweek that the experiment was important for several reasons: "[From a scientific perspective] I think it's a mistake when animals are studied to examine the effects of "X"—in this case, X= spaceflight—without examining the animals' behavior; how the animals behave in response to X could dramatically impact the results of the study. It is especially useful to know that mice find ways to run while in space—so changes observed in spaceflight cannot be simply attributed to inactivity."

She also said that finding mice exercise in space and engage in species-typical behavior at appropriate times of the day is encouraging in terms of animal welfare—it appears to show the mice tolerate and adapt to spaceflight.

"Given access to a running wheel, mice will voluntarily run," Hotz Vitaterna said. "Even wild mice will run in a wheel placed outdoors. I think the "race-tracking" is a way the space mice have figured out to run as though they have a wheel. Now I wonder if it wouldn't make sense to provide ground control groups with an exercise wheel so they can keep up with the space mice."