Rats are even smarter than we thought: they can learn a set of abstract rules and apply them to completely new situations - something we thought previously only humans, other primates and one or two species of bird can do.
When a toddler learns to speak and understand language, they don't have to learn the meaning of every possible word combination. Instead, they learn the 'rules' of the language, and apply these rules to new words as they learn them. Now, I'm not suggesting that Rats learn to speak, but they do seem to be capable of the same kind of rule transfer.
Writing in Science, University College London 's Robin Murphy and colleagues conditioned rats to expect food after being played a certain sequence of tones - this is called Pavlovian conditioning and the rats responded as you would expect, looking for food after the right sequence. They were fed after hearing the sequence ABA, and BAB, but not after the sequence AAB, BBA, BAA or ABB.
They were then tested again using different tones -if they responded to the right sequence, regardless of what tones they were, they would have transferred the sequence rule to a new set of conditions. It's been shown that songbirds do not recognize a song that has been transposed by an octave, so different tones should be treated as a completely new situation.
They were played sequences of CDC, DCD, CCD, DCC, DDC and CDD - and the researchers again measured how long the rats spent looking for food after each sequence. The rats spent much more time looking for food after the sequences they had learned with different tones - in this case CDC or DCD. This shows that rats are able to apply abstract rules to a novel situation, a key element of problem solving.
So both rats and humans have evolved a mechanism to transfer abstract rules to new situations, a key skill for the development of language which seems to set us so far apart from the rest of the animal kingdom. This ability makes up part of the neurological 'toolkit' we have for solving problems, probably part of why both rats and humans are successful almost everywhere on Earth.