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Songbirds' Brains Provide Clues to Human Speech

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Duke Health News 919-660-1306

DURHAM, N.C. – Analyzing how the brains of songbirds respond
to singing patterns has provided new information about how
humans learn to communicate with each other, according to Duke
University researchers.

A study in the latest edition of Nature reveals that
individual cells in the brain display remarkably similar
patterns of activity whether a sound associated with
communication is being heard or produced. The study was
performed using songbirds that sing back and forth in the wild
to defend territory.

The researchers think that these specialized cells in the
brain may be especially important for helping an individual be
both a sender and a receiver in communication.

"The ability of the animals to communicate with each other
through song and their ability to learn their vocal signals
from other birds provide a powerful system for understanding
how the brain enables learned forms of communication, including
human speech," said Professor Richard Mooney, a Duke University
Medical Center neuroscientist who led the research. The study
was supported by the National Institute of Deafness and Other
Communication Disorders and the National Science
Foundation.

"These birds have a small and distinct repertoire of songs
that they can broadcast over a hundred yards or more," Mooney
said. "We found certain neurons responded nearly identically
when the bird heard or sang a certain song in its repertoire.
This correspondence provides the first demonstration of
so-called 'mirror neurons' in vocal communication."

The researchers used a miniature device that recorded the
activity of single neurons in the brains of swamp sparrows as
they listened to songs presented through a speaker and
subsequently sang them back.

"We feel this work is especially unique because making
neural recordings in freely behaving wild songbirds like we did
is a bit like balancing a small pebble on the end of a sewing
needle while in a stiff breeze," Mooney said.

When the bird was listening, particular cells could only be
excited by a specific song in the bird's repertoire or by a
highly similar song of another swamp sparrow. The same cells
also showed a nearly identical pattern of activity when the
bird sang the song.

Mooney explains that the cells' activities were not simply
the result of the bird hearing its own song, but instead arose
from motor circuits in the bird's brain. "It's as if the motor
program in the bird's brain is not only generating the commands
that are used to produce the song, but also providing an
internal estimation of what those signals should sound like
when they are eventually transmitted out of the brain to the
vocal organ," he said.

"Our discovery of these neurons and the fact that they are
located in an area of the songbird brain important to singing
and song perception strengthens the idea that mirror neurons
play an important role in communication," said Duke
neuroscientist Jonathan Prather, Ph.D., first author of the
paper.

Auditory-vocal mirror neurons are located in an area of the
songbird brain that is analogous to speech areas in the human
brain. "In humans, mirror neurons similar to those we found in
the songbird could be the mechanism by which we rapidly decode
speech and generate verbal responses," Mooney said.

Other members of the research team included Duke University
biologists Stephen Nowicki and Susan Peters.

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