May 2, 2008

Songbirds Babble While Learning to Sing

Baby songbirds begin learning to mimic sounds from nature by babbling, researchers at the Massachusetts Institute of Technology said.

The group, which is studying birds and humans to determine how they learn new behaviors, found that immature and adult birdsongs are driven by two separate brain pathways, rather than one that constantly matures.

Damage to the first circuit while the bird is still learning prevents further learning, so the song remains immature, researchers said.

"Birds start out by babbling, just as humans do,'' Fee said, while the adult bird produces a very precise pattern of sound.

The study found that baby zebra finches practice babbling until they achieve the same song as adults.

Previous research had resulted in a discovery that baby zebra finches had two distinct brain circuits for developing their song. The first circuit was strictly for learning, while the other, known as the motor circuit, was used to carry out the song.

So, if the learning circuit in an adult baby finch is damaged, it has no effect on its song because it no longer relies on the learning circuit.

It had been assumed that the motor circuit was just as important to the babbling of baby birds, but no experiments had been done.

Graduate students Dmitiry Aronov and Aaron Andalman co-authored the report found in the May 2 issue of Science.

They found that once they disabled a part of the motor circuit known as HVC, the babies continues to sing, which implied that another part of the brain was producing the babble.

Authors were then able to show that a part of the learning circuit, called LMAN, has a motor function that was previously unknown to scientists. When LMAN was disabled in very young birds, they ceased babbling.

"This tells us that singing is driven by two different motor circuits at different stages of development," said Aronov.

"We've long known that these two pathways develop physiologically at different times, so there's an elegant parallel between our functional findings and what is already known about anatomy."

Authors also noted that LMAN retains its ability to drive babbling even in adulthood.

Fee speculates that these results may apply more broadly to other forms of immature or exploratory behavior, in humans as well as birds.

"In birds, the exploratory phase ends when learning is complete," Fee said.

"But we humans can always call upon our equivalent of LMAN, the prefrontal cortex, to be innovative and learn new things."


Image Courtesy: Martin Pot (Wikipedia)


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