October 11, 2012

Mice Are Capable Of Learning To Sing; Sort Of

Lawrence LeBlond for - Your Universe Online

Learning to adapt voice is a trait commonly shared among humans, bats and several songbirds, as well as some larger mammals. But a new study, published in the October 10 issue of the journal PLoS ONE, has taken this vocal attribute to new heights after discovering that mice also have the ability to change their voices.

The finding contradicts the long-standing assumption that mice cannot learn to adapt their voices. Although it was previously known that mice use ultrasonic noises, often dubbed as "song," to attract their mates, it had never been demonstrated that these furry little rodents were capable of changing the pitch of the tune.

“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,” said study overseer Erich Jarvis, a neurobiologist at Duke University.

“If we're not wrong, these findings will be a big boost to scientists studying diseases like autism and anxiety disorders,” said Jarvis. “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.”

He noted that this finding is controversial because it contradicts those long-held beliefs that mice cannot learn to adapt their voice. However, the research indicates that the vocal communication pathways in the brains of mice are more similar to those in human brains than to sound-making circuits in the brains of chimpanzees and other non-human primates.

The results of the study also contradict other recent studies that found mice do not match pitch or have deafness-induced vocalization changes.

The study, which also appears in the journal Brain and Language, indicates that ultrasonic vocalizations in mice can be learned based on the sounds they hear. Jarvis, his research partner, Gustavo Arriaga, also of Duke, and a colleague from Tulane University, show for the first time that mice have similar brain behavioral mechanisms involved in vocal learning and can learn new vocal patterns.

In birds, this vocal trait is limited to parrots, hummingbirds and songbirds. In the mammal kingdom the traits were previously known to be limited to humans, whales, dolphins, elephants, sea lions and bats. Surprisingly, the specific behavioral and neurological mechanisms that play a role in vocal adaptation have yet to be found in non-human primates.

Now, researchers can add mice to the list of animals that have the so-called mechanisms that allow for vocal adaptation.

“This is a very important study with great findings,” Kurt Hammerschmidt, an expert in vocal communication at the German Primate Center who was not involved in the study, said in a statement. While remaining cautious about some of the claims in the study, he suggested that if mice can learn vocalizations they may become a good model in the studies of the evolution of language on a genetic scale.

In their study, Jarvis and colleagues tested male mice for vocal learning traits as part of a larger project to study speech evolution in humans. Because scientists held onto the belief that vocal learning was unique to a limited number of species in the animal kingdom, the researchers did not expect to find anything significant.

Since scientists have never found the mechanisms in other animals than the ones already known, "I almost expected every experiment in mice to fail," Arriaga said in a statement.

The team first used gene expression markers, which lit up neurons in the motor cortex in the brains of the mice as they sang. They then damaged these neurons and observed that the mice could not keep their songs on pitch or repeat them as consistently, similar to what occurs when mice become deaf.

Using an injectable tracer, the team were able to map the signals that control song as they moved from neurons in the motor cortex to those in the brainstem and then on to the muscles in the larynx.

“This direct projection from the mice's forebrain to the brainstem and muscles was the biggest surprise,” remarked Jarvis.

As part of their studies, Jarvis and colleagues put two male mice in a cage with a female. After seven to eight weeks the team noticed the males gradually learned to match the pitch of their songs to one another. The team tested more than 14 mice and repeated the experiment twice before confirming the results.

Even as they were able to replicate their findings in each subsequent experiment, the researchers state that this is a limited form of vocal learning and they do not yet know whether other more complex features, such as syntax and frequency modulation, can be learned in mice.

While he was intrigued by the first part of the study´s findings, Hammerschmidt said he remained skeptical of the latter experiments.

Jarvis and Arriaga's "pitch convergence story is less convincing," he said. Scientists have observed pitch convergences in non-vocal learners and the number of tested animals in this study could be too low to determine whether the discovered effect is reliable, he added.

Jarvis disagreed with Hammerschmidt, but did note that more research was needed to see if mice can learn more advanced vocalizations than just how to fine-tune their pitch.

“Our results show that mice have the five features scientists associate with vocal learning. In mice, they don't exist at the advanced levels found in humans and song-learning birds, but they also are not completely absent as commonly assumed,” he said.

The study was funded by Howard Hughes Medical Institute (HHMI), the National Science Foundation (NSF), and the National Institutes of Health (NIH).

Click here to listen to mice song