Rats living in fancier digs seek richer rewards

LOOKING UP
Some rats in this lab showed a rodent version of optimism — taking chances more often that chocolate would be available — after their living conditions were upgraded.N. Brydges


Give lab rats a week at the Rodent Ritz and they’re not thinking Cheerios so much anymore. They’re thinking chocolate.

Upgrading their real estate changed rats’ bias in guessing what to do about ambiguous cues in a lab test, says cognitive neuroscientist Nichola Brydges of the University of Edinburgh.

A week after moving into a bigger, better furnished cage, rats had grown more likely to take a chance that a confusing signal would lead to a bit of chocolate to eat — an indication of optimism — instead of just half a Cheerio. Rats had been trained that a wrong choice in responding to a cue would mean not getting any reward, so they had an incentive to choose correctly, Brydges and her colleagues report in an upcoming issue of Animal Behaviour.

Experiments have shown that like people, other animals can develop a pessimistic bias under adverse conditions. But, says Brydges, “It is rare for people to look at what makes animals optimistic.” The new rat study is the first to show a clear link between changing an animal’s environment and optimism, she says.

The research team developed a sophisticated means to test for bias in the rats, says Hanno Würbel of Justus-Liebig University in Giessen, Germany, who has analyzed the effects of animals’ lab conditions on experimental results. For example, the study protocol has built-in controls that rule out other possible explanations for the results such as differences in motivation among the rats. “I consider this the most convincing evidence of cognitive bias in animals, and of environmental effects on it, to date,” he says.

To probe for optimism, Brydges and her colleagues trained 12 rats to scamper over sandpaper and then go to one cup if the sandpaper had a fine grain or a different cup if it was coarse-grained. Researchers doled out a lush chocolate reward for one of the grades of sandpaper but the less-exciting cereal for the other. At each presentation of sandpaper, researchers put out just one treat, rewarding the rat only for the correct answer.

But the researchers occasionally presented an ambiguous cue, sandpaper with an intermediate grain. Rats still made a choice and scurried to one of the cups. Before the home makeovers, though, rats on average responded to ambiguous cues rather pessimistically, tending to guess that the right answer was the chocolate-filled cup only about one time in five on average. “I had expected 50/50,” Brydges says.

Half the rats, which stayed in standard laboratory housing, continued to guess the cereal cup was correct most of the time. The rest of the rats — whose new digs had extra-deep wood shavings and such amusements as wood blocks, cardboard tubes and even a plastic house — took a chance on the chocolate cup more than three times in five.

Würbel says he would like to see whether the findings hold in an expanded test. More interesting to him, though, is what would happen after a few weeks when the rats got used to the larger and more complex cage. “In rats,” he says, “it appears to be much more difficult than, for example, in mice to provide an environment that is stimulating enough for the animals to keep them active, inquisitive, and ... possibly ... happy.” It remains to be seen whether the chocolate-seeking optimism is due to the improvement in living conditions, or the passing novelty of the change in conditions.

Susan Milius