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New Findings Help Explain Vocal Learning
and May Guide Search for Brain's Language Center
"To a teacher of languages there comes a time when the world is but a place of many words and man appears a mere talking animal not much more wonderful than a parrot."
Joseph Conrad (1857-1924), Polish-born British novelist, from Under Western Eyes, pt. 1, prologue (1911)
As the late novelist Joseph Conrad once suggested, people may indeed have more in common with vocal-learning birds like songbirds and parrots than we have previously assumed.
In songbirds capable of vocal learning, or imitating the sounds they hear, new findings reveal a highly specialized pattern in the genetic expression of certain brain receptors. These same receptors for the neurotransmitter, glutamate, are also found in mammals, neurobiologist Erich D. Jarvis noted during the annual meeting of the American Association for the Advancement of Science (AAAS).
If further research shows the same specialized receptor pattern in people, the research may help pinpoint the brain's precise language centersa first step toward better understanding language loss associated with strokes, lesions or head injuries. The work, by Jarvis, his student and first author Kazuhiro Wada at Duke University and colleagues Hironobu Sakaguchi and Masatoshi Hagiwara in Japan, is now pending review by the Proceedings of the National Academy of Sciences (PNAS).
"Although it might seem far fetched, I would not be surprised if these ancient receptors could someday help us identify the entire system of brain regions for vocal learning and language in humans in a way that hasn't been done before," said Jarvis, an assistant professor in Duke's Department of Neurobiology.
Like a modern-day Dr. Doolittle, Jarviswinner of the prestigious Alan T. Waterman Award, the National Science Foundation's highest honor for a young scientist or engineerseeks to understand animal "language." He's investigating what structures and molecular events in the brain give six groups of animals a capacity for vocal learning. Imitating the sounds we hear is a rare trait, shared only by certain birds (parrots, songbirds and hummingbirds) and a few mammals (bats, cetaceans in the whale/dolphin family and humans).
As he studies the neural mechanisms behind vocal learning, Jarvis is also pursuing a key question in evolutionary biology: Did the trait of vocal learning emerge independently in all six vocal-learning groups within the past 65 million years, as a now-dominant theory suggests? Or, did all vocal learners share a common ancestor with the trait, but then diverge as a result of subsequent, independent mass extinctions of vocal learning among various animals, including non-human primates? Though this question remains a mystery for now, Jarvis' latest work suggests that the evolution of vocal learning was accompanied by divergent, specialized expression of an ancient gene family in different vocal learning animals. Further, the diversity of expression seems to depend on the complexity of the animal's vocal syntax.
"Whether independent or dependent from a common ancestor, diversity of neurotransmitter receptors in their vocal systems is probably not an evolutionary cause of vocal learning, but a consequence of it, as diverse species-specific specializations can be assumed recent and ongoing evolution," Jarvis, Wada and colleagues wrote in their pending PNAS paper.
Moreover, they added: "With diverse specialization as a rule, it is not too far a stretch to suggest that vocal-learning mammals, including humans, also evolved diverse specialized glutamate receptor expression in vocal areas of their cerebrums and that these are related in part to vocal syntax complexity."
Jarvis received his doctoral degree from The Rockefeller University in 1995. He was one of 52 African American men out of more than 4,300 biologists to receive a Ph.D. in the United States that year. His own pathway to success was inspired by his mother, a woman with an ambitious spirit, and his late father, a talented man who struggled with schizophrenia and periodic homelessness while Erich was a child in New York City's Harlem community. His father's eclectic interests and appreciation for the natural world helped to shape Erich's unique, interdisciplinary approach to his research, making himas former NSF Director Rita Colwell once said"truly a gem" and "the epitome of the modern scientist, crossing between disciplines and ideas."
This research project was funded mostly by a National Science Foundation grant.
15 February 2003