Already famous for swimming through sewers and surviving under subway rails, rats can now claim a more sophisticated talent: thinking about thinking. It's not epistemology, but a study published today in Current Biology reports the first evidence that rats know the limits of their own knowledge--a capacity long thought to belong only to the animal kingdom's top brains.
People experience metacognition, or gauging their own knowledge, on a daily basis; anyone who's ever had a sinking feeling during an exam knows it well. But attempts to detect metacognition in animals have met with little success, in large part because animals can't tell researchers what they're thinking. Scientists must instead rely on behavioral clues: Monkeys place lower bets on their answers when given a difficult test, for example, and dolphins waver when asked to distinguish between two similar sounds. Thus far, however, smaller-brained animals, such as pigeons, have shown no signs of metacognition in the lab.
Would rats be any different? Neuroscientist Jonathon Crystal of the University of Georgia in Athens and his graduate student, Allison Foote, put the rodents to the self-knowledge test by asking them to classify sounds. First, the researchers trained the rats to associate a short burst of static--lasting about 2 seconds--with one lever, and a long burst of static--lasting about 8 seconds--with another lever. Pushing the correct lever yielded a tasty reward of six food pellets; pushing the incorrect lever yielded no food and no chance to try again. The rats also learned that they could get half the reward without making a choice, by poking their nose into a food trough.
Then the metacognition test began. Crystal and Foote placed the rats in a cage with the levers and the food trough and started playing the static sounds. Knowing they could get a bigger reward by pushing the correct lever, the rats shunned the trough and began tapping. But things changed when the researchers made the test more difficult. In a second set of experiments, the team played more intermediate bursts of static that were harder to classify as "short" or "long." This time, the rats were twice as likely to go for the trough and not bother with the levers. "The harder you make the test, the more likely they are to decline [to take it]," says Crystal.
To confirm that the rats were skipping the exam because they knew they'd get the wrong answer, Crystal and Foote repeated the hard test without the food trough. When forced to take the test, the rats performed poorly, just as they probably knew they would. "Rats are capable of reflecting on their internal mental states," Crystal concludes. In that respect, he notes, they behave just as primates and dolphins do.
"It's an important study," says University of California, Los Angeles, metacognition researcher Nate Kornell. "It tells us that the mental processes of rats are more similar to ours than we thought." It may also tell us that supposedly smart animals don't have the market cornered on awareness, he adds, because "if this is true for rats and monkeys, then it's probably true for other mammals as well."