Though they perch far apart on the avian family tree, birds with the ability to learn songs use similar brain structures to sing their tunes.
Neurobiologists at Duke University Medical Center now have an explanation for this puzzling likeness.
In all three groups of birds with vocal learning abilities - songbirds, parrots and hummingbirds - the brain structures for singing and learning to sing are embedded in areas controlling movement, the researchers discovered. The team also found that areas in charge of movement share many functional similarities with the brain areas for singing. This suggests that the brain pathways used for vocal learning evolved out of the brain pathways used for motor control.
These ancient pathways, which power limb and body movements, constrained both the location and circuitry of structures for learning and imitating sounds, theorizes senior author Erich Jarvis, Ph.D., associate professor of neurobiology. The findings may also help solve the riddle of why humans talk with our hands and voice, but chimps can talk only with their hands.
"In its most specialized way, spoken language is the ability to control the learned movements of our larynx," Jarvis said. "It's possible that human language pathways have also evolved in ways similar to these birds. Perhaps the evolution of vocal learning brain areas for birds and humans exploited a universal motor system that predates the split from the common ancestor of birds and mammals."
The results appear in the March 12, 2008 edition of the journal PLoS ONE. The research was funded by the National Science Foundation and a National Institutes of Health Pioneer Award to Jarvis. The collaborative study was co-led by Henrik Mouritsen of the University of Oldenburg in Germany, who was supported by the VolkswagenStiftung, and first author Gesa Feenders, now a postdoctoral researcher at the University of Newcastle, UK.
"This innovative research exemplifies the bold thinking and creative approaches fostered by the NIH Director's Pioneer Award," said National Institutes of Health Director Elias A. Zerhouni, M.D. "The discovery that vocal learning brain pathways are embedded in the parts of the brain that control body movement offers unexpected insights on the origins of spoken language and could open up new approaches to understanding vocalization disorders in humans."
Jarvis and his colleagues examined bird species with vocal learning skills and some without: garden warblers, zebra finches, budgerigars (parrots), Anna's hummingbirds and ring doves. Their technique involved observing and manipulating bird behavior, then recording which genes were active in the birds' brains when the birds were moving and singing in certain ways.
"When we use this behavioral molecular mapping approach, we get gene expression patterns in the brain that light up like MRI images," Jarvis said. The study is the first to map the parts of the forebrain that control movement in birds. The forebrain is the largest part of the brain, and includes the pathways for thought, learning and perception.