Rats appear capable of a complex form of thinking before known to exist only in humans and other primates — the capacity to reflect on what they do or do not know.
"If rats can do it, this capability may be more widespread than imagined," Jonathon Crystal, a comparative psychologist at University of Georgia, told LiveScience.
Humans often are aware of what knowledge they possess or lack and what they are or are not capable of.
"Imagine, for instance, that you're a student going into a classroom to take an exam," Crystal said. "You will often have some idea how well you're going to do on the test. You know before you answer the questions whether you know or don't know the answers. This pretty complex form of cognition, known as metacognition, is at the heart of the human condition."
Increasingly, evidence of metacognition is found in rhesus monkeys and other primates, but little research has been done on it in other mammals. Crystal and his colleague Allison Foote decided to push the limit and see if rats were capable of it.
Rats were given a choice to take a test. If they bailed out of the test by poking their noses into one hole, they received a small reward of food pellets. If they opted in by nudging their snouts into another hole, passing the test resulted in a large reward of pellets, while failure yielded nothing.
The test played the rats noises that were either short (between 2 and 3.6 seconds) or long (between 4.4 and 8 seconds). The rodents then had to classify the recent noise as either long or short by pressing one of two levers. This choice was relatively easy if the noise was either very short or very long—for instance, 2 seconds or 8 seconds. However, the decision was far harder if the noise was easily confused as either short or long — for instance, 4.4 seconds.
The scientists found the rats appeared capable of judging whether they had enough information to pass the test. The more difficult the test was, the more often rodents opted to decline the test.
The discovery of this form of thinking in rats opens up further experiments into the brain anatomy and chemistry underlying metacognition in rats, "which could impact human health," Crystal said. "For instance, two human health issues linked with metacognition that come to mind are Alzheimer's disease and amnesia."
Foote and Crystal detailed their findings yesterday in the online version of the journal Current Biology.