Language has traditionally been accepted as an all or nothing trait, but new research suggests that there may be a continuum of vocal learning.
Male mice, who were previously thought to be incapable of vocal learning, can change their ultrasonic mating songs after hearing the songs of other mice, according to a recently published Duke study. The findings could be used to better understand speech disorders in humans.
Previous research in vocal learning focused on songbirds, but the discovery of mice as vocal learners could have significant implications for understanding communication systems in humans, given that both are mammals, said Gustavo Arriaga, a doctoral student in neurobiology and lead author of the study.
“Having a mammalian model of vocal learning is going to provide new pathways for scientists who are trying to understand communication disorders such as Parkinson’s and even speech loss after stroke,” Arriaga said.
Vocal learning is an animal’s ability to modify the sounds it generates, according to the study published in the scientific journal PLOS ONE. The scientific community used to view animals as either vocal learners or non-vocal learners, said coauthor Eric Zhou, a second-year medical student at Tulane University. The continuum hypothesis, however, posits that there is a range of vocal learning, with basic imitation to creating new speech—like humans do.
“The trait of vocal learning is rare in the animal kingdom,” Arriaga said. “Before [this study] we had no clear example of an animal that was an intermediate.”
Mice are such an intermediate. They require a template—such as another mouse’s mating song—and it appears that they cannot independently create new sounds.
Only a handful of mammals are known to possess this vocal learning trait, Arriaga said. These animals—dolphins, whales and humans—however, are impractical subjects to study in a lab.
The researchers mapped brain activity of the mice while producing their mating songs and found that mice possess a rudimentary version of the neurological pathways associated with vocalization in humans and songbirds. Senior author Erich Jarvis, associate professor of neurobiology, said he is excited to explore potential correlations between rodent and human vocal learning.
“The next steps would be to further our knowledge of similarities and difference between human and mice pathways, be able manipulate them and enhance the pathways in order to advance vocal learning,” he said.
In the future, Jarvis seeks to use the grant from the National Institutes of Health Director’s Pioneer Award, which he received in 2005, to find a way to produce the neurological structures needed for vocal learning in species that do not have them.
Richard Mooney, George Barth Geller professor of neurobiology and a researcher of vocal learning in songbirds, said the study is important because it maps structures for vocalization in mice, an area previously unexplored.
But he questions whether mice should be categorized as a species capable of vocal learning, adding that there are other possible explanations for the changes in the mating songs such as environmental factors.
“It is important to define what is learning,” he said. “You can loosely define learning as change, or you can define it as adapting in order to improve.”
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