By James Gorman
If an exercise wheel sits in a forest, will mice run on it?
Every once in a while, science asks a simple question and gets a straightforward answer.
In this case, yes, they will. And not only mice, but also rats, shrews, frogs and slugs.
True, the frogs did not exactly run, and the slugs probably ended up on the wheel by accident, but the mice clearly enjoyed it. That, scientists said, means that wheel-running is not a neurotic behavior found only in caged mice.
They like the wheel.
Two researchers in the Netherlands did an experiment that it seems nobody had tried before. They placed exercise wheels outdoors in a yard and in an area of dunes, and monitored the wheels with motion detectors and automatic cameras.
They were inspired by questions from animal welfare committees at universities about whether mice were really enjoying wheel-running, an activity used in all sorts of studies, or were instead like bears pacing in a cage, stressed and neurotic. Would they run on a wheel if they were free?
Now there is no doubt. Mice came to the wheels like human beings to a health club holding a spring membership sale. They made the wheels spin. They hopped on, hopped off and hopped back on.
“When I saw the first mice, I was extremely happy,” said Johanna H. Meijer at Leiden University Medical Center in the Netherlands. “I had to laugh about the results, but at the same time, I take it very seriously. It’s funny, and it’s important at the same time.”
Dr. Meijer’s day job is as a “brain electrophysiologist” studying biological rhythms in mice. She relished the chance to get out of the laboratory and study wild animals, and in a way that no one else had.
She said Konrad Lorenz, the great-grandfather of animal behavior studies, once mentioned in a letter that some of his caged rats had escaped and then returned to his garden to use running wheels placed there.
But, Dr. Meijer said, the Lorenz observation “was one sentence.”
For the experiment, the wheels were enclosed so that small animals could come and go but so that larger animals could not knock them over. Dr. Meijer set up motion sensors and automatic video cameras. Several years and 12,000 snippets of video later, she and Yuri Robbers, also a Leiden researcher, reported the results. They were released in the Proceedings of the Royal Society B.
Gene D. Block, chancellor of the University of California, Los Angeles, was not involved with the paper but knows Dr. Meijer and had seen the wheel set up in her garden. He said the study made it clear that wheel-running is “some type of rewarding behavior” and “probably not driven by stress or anxiety.”
Mice accounted for 88 percent of the wheel-running events, and spent one minute to 18 on the wheel. The other animals each accounted for less than 1 percent. Frogs, though there were very few, were seen to get on the wheel, get off and get back on.
Russell Foster, a circadian rhythm researcher at Oxford University, said he read the paper and sent it out to other scientists on behalf of the Proceedings and was delighted when peer reviews from other scientists were positive.
Marc Bekoff, a professor of ecology and evolutionary biology at the University of Colorado who is active in the animal welfare movement, said in an email that he thought the paper did show that wheel-running could be a “voluntary activity,” but that mice in labs may be doing more of it because of the stress of confinement.
“Wild bears will often pace back and forth,” he wrote, “but in captivity, the rate of doing it seems to be greatly heightened.”
As to why the mice, frogs or perhaps even slugs run, or move, on the wheel, Dr. Meijer said she thought that “there is an intrinsic motivation for animals, or should I say organisms, to be active.”
Huda Akil, co-director of the Molecular and Behavioral Neuroscience Institute at the University of Michigan, who has studied reward systems, said: “It’s not a surprise. All you have to do is watch a bunch of little kids in a playground or a park. They run and run and run.”
Dr. Akil said that in humans, running activates reward pathways in the brain, although she pointed out that there are innate differences in temperament in all sorts of animals, including humans. Rats that do not like to run can be bred. And plenty of people do all they can to avoid jogging, cycling and elliptical machines.
Presumably, the same is true of wild mice. While some were setting the wheel on fire with their exertions, others, out of camera range, may have been sprawled out on the mouse equivalent of a lounge chair, shaking their whiskers in dismay and disbelief.
Thanks to Dr. Nakamura for bringing this to the attention of the It’s Interesting community.