An international team of researchers mapping the genomes of birds has discovered a structure in the brains of parrots that likely explains their ability to mimic human speech.
The structure identified by the Duke University-led research team may eventually provide insight into human speech disorders, said Mukta Chakraborty, a post-doctoral researcher in neurobiology at Duke.
“We always wondered why parrots are able to imitate human speech,” Chakraborty said. “Now, we have found something that hasn’t been discovered over the last three decades of study. Everyone is very excited about it; it has created quite a ruffle.”
The team’s findings were published this summer in the journal Plos One.
Previous studies involving the speech center in parrots’ brains looked only at one type of parrot – the budgerigar or common parakeet. But with brain tissue contributions from co-investigators in Denmark and the Netherlands, the researchers were able to examine eight additional parrot species, including cockatiels, Amazon parrots, lovebirds, a blue and gold macaw, a kea and an African grey parrot.
What they found common in parrots was an outer shell surrounding the known vocal learning core. Songbirds and hummingbirds have the core ... but not the outer shell.
“In parrots, not only do their brains have a core structure but an extra outer shell in the region that controls vocal learning,” Chakraborty said. “This could be the brain structure that allows them to identify all these kinds of sounds, including human speech.”
However, the difference is not “glaringly obvious,” which is why it was previously overlooked, Chakraborty noted.
Many types of animals are vocal learners, including bats, whales, seals and elephants, as well as songbirds, parrots and hummingbirds, but most only mimic sounds made by their own species.
“Among these three vocal learning birds, we’ve always known parrots are different, because they are able to copy birds of other species as well as human speech,” Chakraborty said.
Neurons within the vocal centers are thought to play a role in vocal learning and even some motor behaviors, she added. The need to listen and respond to sounds made by the birds’ parents or siblings is likely responsible for development of this ability, she said.
Among the species of birds studied by the international team was one of the oldest in the world, the kea parrot.
“Twenty-nine million years ago, the core and shell structure evolved in this bird,” Chakraborty said. “Just the fact that it goes so far back indicates that the parrots evolved away from hummingbirds and songbirds with the core and shell structure.”
By studying these specialized structures, Chakraborty said scientists should be able to learn more about how gene therapies may be used to address speech disorders in humans.
“The biggest issue is to find the genes involved in how we speak and how we learn to talk,” she said. “That will help us in understanding speech disorders. Now we rely mostly on behavioral therapy.”
Chakraborty works in the lab of Erich Jarvis, an associate professor of neurobiology at Duke and a Howard Hughes Medical Institute Investigator.
Next up are further studies to determine what happens when the shell structure is removed from the brain of a parrot.
“In our next set of experiments, I think the question that we are going to investigate is what happens when you we surgically ablate or remove the structure,” she said. “If we then put them through behavioral testing, would it then be able to identify other species? And if the shell is damaged, can I reverse that later on? There are so many questions we have to answer.”
If human brains function similarly to produce speech, the investigation could lead to possible cures for speech disorders, including those caused by autism, she said.
“One of the main goals is to use the birds and to understand the genetic makeup and footprint, learn what is going on in the specialized shell structure, and what is different in terms of the gene.”
“We can take that the information and get an idea when there is a defect in a gene, how to design gene therapies to address speech disorders.”