Do mice learn to sing the way humans learn to talk?
Mice can learn new songs from one another in the same way as human beings and song birds, scientists say they were surprised to discover.
The finding contradicts a 60-year-old assumption that mice don't have vocal learning traits at all.
"We are claiming that mice have limited versions of the brain and behavior traits for vocal learning that are found in humans for learning speech and in birds for learning song," says Duke University neurobiologist Erich Jarvis.
"If we're not wrong, these findings will be a big boost to scientists studying diseases like autism and anxiety disorders. The researchers who use mouse models of the vocal communication effects of these diseases will finally know the brain system that controls the mice's vocalizations."
His research suggests the vocal communication pathways in mice brains are more similar to those in human brains than they are to the sound-making circuits in the brains of chimpanzees and other non-human primates.
To come to this conclusion, the team first used gene expression markers, which lit up neurons in the motor cortex of the mice's brain as they sang. They then damaged these song-specific neurons in the motor cortex and observed that the mice couldn't keep their songs on pitch or repeat them as consistently.
They also used an injectable tracer, which mapped the signals controlling song as they moved from the neurons in the motor cortex to those in the brainstem and then to the muscles in the larynx.
"This direct projection from the mice's forebrain to the brainstem and muscles was the biggest surprise," says Jarvis.
More controversial, though, is the team's finding that mice can learn a vocalization the way human beings and song birds do. This is based on the observation that when two male mice were placed in the same cage with a female, the males' pitch began to converge after seven to eight weeks. The team tested 24 male mice and did the experiment twice to confirm the result.
However, Kurt Hammerschmidt, an expert in vocal communication at the German Primate Center who was not involved in the study, is skeptical, calling the pitch convergence results 'less convincing'.
Scientists have previously observed pitch convergences in non-vocal learners, he says, and in any case the number of tested animals in the study could be too low for the findings to be reliable.