Babbling babies and birdsong may not sound alike, but learning how to vocalize happens in similar ways in both human and bird babies.
New research has found that birds use the left side of the brain for perceiving and producing song, just as humans do for speech. This suggests that the bird brain may hold clues for how humans acquire and produce speech.
Many, but not all, songbirds have to learn their songs by listening and imitating. Some birds like canaries can pick up more than one song, but zebra finches learn one song and stick with it their whole lives. Monkeys and apes oddly do not learn but rather appear to be born with a set of vocalizations.
“It’s surprising that our closest relatives don’t behave in that respect as we do,” said neurobiologist Johan Bolhuis of Utrecht University in the Netherlands, one of the authors of the study, which is published in the Proceedings of the National Academy of Sciences.
Zebra finches, however, learn to vocalize from their parents – females do not sing – just like humans do. With previous research showing strong neuroanatomical similarities between bird and human brains, Bolhuis and colleagues studied the zebra finch to see if birdsong is dominated by one part of the brain the way language is in humans.
Two groups of finches, adults and adolescents that were still in the “babbling” phase, were played their father’s birdsong, a novel song, or silence. The researchers were particularly interested in two avian brain regions, NCM and HVC, which are analogous to the human areas for speech perception and production, respectively.
HVC, the area involved in singing itself, had more active neurons in the left hemisphere of the brain for all conditions, in both the adolescent and adult finches. This left-dominance for speech processing also is present in human infants and adults in the homologous brain region, called Broca’s area.
The neural response in NCM was different for adult and adolescent finches. The left hemisphere was much more active when the young finches heard their father’s song. This left brain dominance is “similar to (when) the human infant hears its mother’s voice vs. a novel voice,” said Bolhuis, and is also related to accessing and forming memories. The better the young finches were at reproducing their father’s song, the more left-hemisphere-dominant the brain activity was.
For the adult finches, NCM activation was the same across hemispheres, but was still stronger for the familiar song than for silence.
“We knew that there was a division of labor in the bird brain as in the human brain. This similarity (between finches and humans) is intriguing,” Bolhuis said.