To woo females, male mice whistle complex songs at ultrasonic frequencies. Scientists have assumed these tunes are hardwired in their tiny mouse brains and doubted that rodents modify their songs after hearing others — a cognitive feat similar to vocalizations by birds and some mammals, including dolphins, bats and humans.
To test whether feedback had a role in mouse songs, neurobiologist Gustavo Arriaga and colleagues at Duke University deafened adult mice and found that, surprisingly, their songs degraded over time; they were no longer able to maintain a precise pitch. Young hearing-impaired mice fared even worse, producing squawks rather than the usual whistles.
In their next experiment, Arriaga placed a male strain of mouse that had what’s considered a “tenor” voice inside a soundproof cage with a “baritone” so the two mice could only hear each other. In eight weeks of experiments, the tenors tended to change their pitch to match the baritones as they tried to court a female.
The secret to this skill probably lies in the animals’ brain structure. Arriaga has identified a direct connection from the motor cortex, which controls fine motor skills, to the brain stem, which controls the larynx. The link, he believes, creates a feedback loop between singing and hearing, but so far that’s just a hypothesis.
“This gives us the basis for explaining why mice are able to do this and other animals aren’t,” says Arriaga. Mice, more convenient research subjects than, say, dolphins, can be models for studying the genetics and neurobiology of vocal learning.
The next step is to find out if mice can go beyond tweaking their pitch and incorporate entirely new syllables in their repertoire, like parrots can.
Hear the mice for yourself: