Young birds 'babble' before learning how to sing
Washington, May 2 : Just like human infants, baby birds too babble before they learn how to sing.
The discovery has researchers excited as it sheds new light on how birds, and perhaps people, learn new behaviours.
Researchers at Massachusetts Institute of Technology have found that immature and adult birdsongs are driven by two separate brain pathways, rather than just one pathway that slowly matures.
"The babbling during song learning exemplifies the ubiquitous exploratory behaviour that we often call play but that is essential for trial-and-error learning," said Michale Fee, the senior author of the study and a neuroscientist in the McGovern Institute for Brain Research at MIT and an associate professor in MIT's Department of Brain and Cognitive Sciences.
Previous research had shown the zebra finch has two brain circuits dedicated to song, one for learning and another - known as the motor circuit - for producing the learned song.
Damage to the first circuit while the bird is still learning prevents further learning, so the song remains immature.
Yet in an adult that has already learned its song, disabling the learning circuit has no effect on song production.
Scientists assumed the motor circuit was equally important in producing baby birds' babbling, but no research had been conducted.
The new study that included graduate students Dmitriy Aronov and Aaron Andalman involved temporarily disabling parts of the brain, and record from neurons in the singing bird.
When they disabled a part of the motor circuit known as HVC in these very young birds, the babies continued to sing, implying that some other brain region produces the babbling.
The researchers suspected a key component of the learning circuit, called LMAN, has a previously unknown motor function.
They confirmed this by showing that when LMAN was disabled, the immature birds ceased babbling.
"This tells us that singing is driven by two different motor circuits at different stages of development. 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," Aronov said.
The researchers also found that LMAN retains its ability to drive babbling even in adulthood.
Disrupting HVC in adults caused the birds to revert immediately to babbling, suggesting that LMAN can take over again if the more powerful signals from HVC are blocked.
Fee speculates that these results may apply more broadly to other forms of immature or exploratory behaviour, in humans as well as birds.
"In birds, the exploratory phase ends when learning is complete. But we humans can always call upon our equivalent of LMAN, the prefrontal cortex, to be innovative and learn new things," he said.
The study is published in the May 2 issue of Science.