Neuroscientists who study zebra finches could tell you not only that these songbird tunes designate the birds' territory and impress potential mates, but these researchers could map out which neuronal pathways in the brain allowed the birds to learn and produce their characteristic song in the first place.
Scientists first began to investigate how zebra finches learn to sing in the 1950s. Since that time, researchers have deciphered the inner workings of the brains of these small, colorful, native Australian birds and gained insights into how they, and perhaps other animals, learn and communicate.
"It's been known for a while that there's an anatomy of connections in the bird's brain that let it learn and produce song," said David Rosenfield, MD, a professor in the Department of Neurology at Baylor College of Medicine and director of the Speech and Language Center . "Just as a bird learns to produce song, we learn to produce sound."
Just as infants must be exposed to language to speak, zebra finches need to hear song early in life to be able to produce it. In order to become 'fluent' in their individual song, they need to practice it repeatedly (even during their sleep, according to one study), like youngsters need to babble before they learn to talk.
In addition, birds have specialized areas of their brains devoted to communication, just as people do, said Rosenfield, and in both species there is a hierarchy between areas, with some areas controlling others. The general anatomy of the brain differs significantly between people and birds, but at a molecular level much remains the same.
Learning to sing
To learn their song, which is as individualized as fingerprints are for people, a male zebra finch chick must hear an adult sing before it is 65 days old, and it must practice its own song before it is 90 days old. Only the males produce song. If the chick's hearing is disrupted so that it can't hear a song, or its vocal system is disrupted so it can't practice, the birds won't learn how to sing their song.
Once the bird has learned the song, however, the neurons that are in charge of producing song take over, and disrupting the learning pathway has no effect.
For researchers, these well-defined pathways with an easily measured outcome (bird song) provide an excellent opportunity to study learning and memory at all levels in the brain. Plus, the birds are easy to keep and breed, reach sexual maturity early, can live to be around seven years old, and have small brains that are easy for experimental work. One drawback, however, is that researchers don't know too much about the genetics of the birds, so they can't create birds lacking or overexpressing a particular gene of interest.
Only about 20 labs nationwide work with zebra finches as a model organism, but for examining questions related to how language is learned and produced, they are just what is needed, said Santosh Helekar, MBBS, PhD, an assistant professor in the Department of Neurology at Baylor.
"If you are interested in communication, I don't think there is a better model than zebra finches," said Helekar. "You could use some form of primate, like a smaller monkey that used sound, but it would be much more difficult."
Helekar and Rosenfield are using zebra finches to develop the first animal model of stuttering.
Researchers can convert the songs of zebra finches into a chart called a sonogram, which displays the frequencies of the notes over time. By studying these sonograms, the BCM scientists noticed that in about 5 percent of the birds, one note is repeated in the song, just like people who stutter involuntarily repeat sounds.
"These errors could be repetitive and nonvoluntary," said Rosenfield. "We presume these are nonvoluntary because the frequency of the repetitions are so regular. They wouldn't be able to do that voluntarily."
The investigators have also done studies where they have stuttering birds raise chicks born to normal parents. They found that just over half of the normal chicks incorporate repeating notes into their song, although these repeats are different from the ones made by stutterers. In addition, when the foster chicks were placed back with normal singers, they often fix some of the repeats in their song.
"That means at some level they don't want it," said Rosenfield. He and his colleagues hope to use this model to see how they can improve the stuttering or make it worse, and to study how cells in the brain might learn to change their song.
"We're not just looking at stuttering, we're looking at how a cell learns," said Rosenfield.
Helekar is also investigating how birds' brains respond when they hear the songs of other birds, and how different chemicals involved in various brain circuits work to modulate the storage of memories.
Work with these birds "contributes to the common efforts of neurobiologists," he said. "It explains how the brain works, how it represents memories, how behaviors are undertaken by the brain, and how perceptions take place."
In fact, there is much that neuroscientists can learn from the "birdbrained."