Bird study casts light on how vocal learning evolved

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Washington, March 12 : Neurobiologists at Duke University Medical Center have discovered that songbirds, parrots, and hummingbirds use similar brain structures to sing their tunes.

The researchers say that in the three groups of birds, who possess vocal learning abilities, the brain structures for singing and learning to sing are embedded in areas that control movement.

According to them, areas in charge of movement share many functional similarities with the brain areas for singing, a finding that suggests that the brain pathways used for vocal learning evolved out of the brain pathways that power limb and body movements.

Dr. Erich Jarvis, associate professor of Neurobiology, theorized that the motor-controlling brain pathways constrained both the location and circuitry of structures for learning and imitating sounds.

He said that the findings might be helpful in unravelling the riddle as to why humans talk with their hands and voice, but chimps talk only with their hands.

"In its most specialized way, spoken language is the ability to control the learned movements of our larynx. 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," Jarvis said.

National Institutes of Health Director Dr. Elias A. Zerhouni added: "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."

During the course of research, the researchers examined bird species with vocal learning skills and some without-like garden warblers, zebra finches, budgerigars (parrots), Anna's hummingbirds and ring doves.

Their technique involved observing and manipulating bird behaviour, and then recording which genes were active in the birds' brains when they were moving and singing in certain ways.

"When we use this behavioural molecular mapping approach, we get gene expression patterns in the brain that light up like MRI images," Jarvis said.

While all birds vocalize, for most of them these sounds are genetically hardwired. Only songbirds, parrots and hummingbirds have the ability to learn songs. This type of vocal learning is similar to the way that humans learn to speak, Jarvis said.

"Based on the data, we think that the brain has a pre-existing substrate, namely a forebrain motor pathway, that led to the evolution of similar vocal learning pathways in three different bird families," Jarvis said.

He further said that the connection between movement and vocal learning also extended to humans, as human brain structures for speech also lie adjacent to, and even within, areas that control movement.

The results appear in the journal PLoS ONE.

ANI

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