CAMBRIDGE, MA. -- APRIL 7, 2005 -- An experienced birder can identify a songbird, sight unseen, by its distinctive notes. For a long time, scientists have yearned to understand how a young bird's clumsy chirps and warbles morph into the stereotypical and oft rhapsodized melodies of its kin. Now, neuroscientists at the McGovern Institute for Brain Research at MIT show for the first time how a particular brain region serves as the source of vocal creativity that a bird needs to perfect its song.

"It's an extraordinary finding," says Sarah Bottjer of University of Southern California. "It's the first demonstration of a neural circuit that seems to contribute directly to motor variability, and it strongly suggests that variability is critically important to learning."

The songbird's creative, trial-and error type of learning provides an ideal model for studying similar processes in humans, such as how a baby's babbling takes on the conversational cadences and recognizable syllables of mama and papa. Likewise, the brain pathways involved in birdsong have a human counterpart, the still poorly understood basal ganglia circuit, so birds may have something to teach us about our own brains.

"The question we're trying to answer is how a young bird learns its song," says Michale Fee of the McGovern Institute about his recent study, published online in advance of the May 2005 free access journal, Public Library of Science Biology. "We've known there are several brain areas involved. One is a motor circuit for producing the song, and the other is a learning circuit, called the AFP (for anterior forebrain pathway), that sends its output to the motor system."

Normally, the young zebra finch nursery resounds with ever new, imperfect variations on the acoustic themes of the adult song repertoire. Gradually, the youngsters' songs become less variable and more true to the old standards. Some years ago, Bottjer had observed that disabling a young finch's AFP circuit stopped the learning in midstream. The bird still sings, but never learns the right song. To explain this effect, scientists theorized that the AFP circuit helps the juvenile compare its immature efforts with its parent's (usually the father's) example. Without such comparisons, the bird cannot know how badly it sounds or that it needs to try harder. That hypothesis, however, did not explain how all the playful variability in the little bird's romper room babbling arose in the first place. For years, nobody had followed up on that question, even though Darwin himself had compared a baby bird's erratic chirping to a human baby's babbling.

"We framed the question in a different way," Fee says of his research with his post-doc Bence P. Oelveczky and graduate student Aaron Andalman. "We said: this young bird is being creative, exploring many different sounds through trial and error. We hypothesized that the AFP is the source of this creativity, generating the variations, rather than comparing them."

To test this theory, Fee's lab studied finches that were just old enough to begin their vocal explorations. The researchers temporarily inactivated the part of the AFP connecting to the motor system used in producing songs. That inactivation shut down all the youthful variability, temporarily stranding the young finch with an immature version of the song.

These results suggested that the AFP circuitry itself causes the juvenile's unabashed experimentation with various sounds and sequences, explains Fee, and such explorations are essential to learning songs. Deactivating the AFP after a bird had already learned the correct song had no affect on its continuing proficiency, indicating that the AFP plays its crucial role during the learning stage, not throughout life.

Noisy signals promote practice until perfect

The researchers then wanted to know how the AFP facilitates such youthful exploration. They predicted, correctly it turns out, that the AFP neurons would produce random bursts of activity coinciding with new variations in the practice routine. Using a micro-recording device for neuronal activity that Fee had previously developed, they discovered that the normal firing patterns of the AFP output neurons were very noisy, with unpatterned spikes of fairly intense signals.

"We think the bursts of these neurons 'kick' the motor pathway that is producing a song, jarring it out of the routine and making it sing something new," Fee explains, "as if someone bumps your elbow while you are playing piano and your fingers strike different keys." Then another, still unexplained, pathway compares that variation to the bird's memory of the father's song. If it sounds right, a feedback mechanism tells the bird: 'That's right, try to do that again.' Gradually, the bird gets it right more often and learns to resist the AFP's rowdy interference. Like a novice choir coming into harmony after numerous rehearsals, it eventually sings only the songs of its elders.

"These results show how the brain produces the explorations needed to learn complex behaviors in ways that are relevant to humans," Fee comments. "We know the human homolog of the AFP, basal ganglia circuitry, is essential to motor learning, and is also involved in habitual behaviors, but we don't know what it actually does. It's very exciting to see a specific role for this circuit in birds." These studies may eventually apply to human diseases affecting motor abilities. Parkinson's disease, for example, destroys neurons that are necessary for the functioning of the basal ganglia.

"It's pretty amazing that here's an organism that enables a direct investigation of how animals learn motor activities," says Bottjer. "We can't do these studies with human babies."

Public Library of Science Biology, Vol 3, Issue 5, May 2005. Online March 29, 2005. Vocal experimentation in the juvenile songbird requires a basal ganglia circuit, Bence P. Oelveczky, Aaron S. Andalman, Michale S. Fee.

Synopsis: To a Zebra Finch: How the Brain Cultivates Birdsong.

About the McGovern Institute at MIT

The McGovern Institute at MIT is a research and teaching institute committed to advancing human understanding and communications. Led by a team of world-renowned, multi-disciplinary scientists, The McGovern Institute was established in February 2000 by Lore Harp McGovern and Patrick McGovern to meet one of the great challenges of modern science - the development of a deep understanding of thought and emotion in terms of their realization in the human brain. Additional information is available at: http://web.mit.edu/mcgovern/

Lyn Chamberlin
skyePR
978-443-0400
lyn@skyepr.com

###