This story is from the category The Brain
Date posted: 17/01/2010
Scientists at Duke University Medical Center have identified neurons in the songbird brain that convey the auditory feedback needed to learn a song.
Their research lays the foundation for improving human speech, for example, in people whose auditory nerves are damaged and who must learn to speak without the benefit of hearing their own voices.
"This work is the first study to identify an auditory feedback pathway in the brain that is harnessed for learned vocal control," said Richard Mooney, Ph.D., Duke professor of neurobiology and senior author of the study. The researchers also devised an elegant way to carefully alter the activity of these neurons to prove that they interact with the motor networks that control singing.
The study, supported by an NIH grant, was published online in Neuron on Jan. 13.
Vocal learning isn't a simple process. "One challenge the brain faces when trying to learn a new behavior is that it only receives feedback about performance tens or even hundreds of milliseconds after it has generated the motor commands controlling that performance," Mooney said. "The challenge is pushed to an extreme if the brain has to use this sensory information in a retrospective way and still make corrections with millisecond precision, as humans and songbirds do when they learn to vocalize."
The problems that juvenile birds solve when they learn a song from a tutor bird are similar to the problems humans solve when we learn to speak, and birds and humans exploit similar neural systems to reach this solution, Mooney said.
The major question of this research was how the brain encodes and harnesses auditory feedback to shape the vocal performance in juvenile birds that are learning to sing.
In a painstaking experiment, lead author Huimeng Lei, Ph.D., used fine microelectrodes to locate neurons that become active in the pupil's brain when it hears its own song, Mooney said. "This was a very difficult procedure that had to be exquisitely accurate. Huimeng was able to get the recordings working just right to locate the feedback-sensing neurons."
Once the scientists knew they had located the correct set of neurons, they passed a brief pulse of electricity through the implanted electrodes to alter neural activity associated with one of the notes that the pupil was learning to sing.
"We think that the stimulation alters what the pupil bird perceives, and it is this altered perception that results in the note becoming distorted (as it sings the song back)," Mooney said. "In contrast, if we stimulated directly in the motor network (which produces the note) we would trigger an immediate distortion of the targeted song syllable."
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