Parrots, like the one in the video above, are masters of mimicry, able to repeat hundreds of unique sounds, including human phrases, with uncanny accuracy. Now, scientists say they have pinpointed the neurons that turn these birds into copycats. The discovery could not only illuminate the origins of bird-speak, but might shed light on how new areas of the brain arise during evolution.
Parrots, songbirds, and hummingbirds—which can all chirp different dialects, pick up new songs, and mimic sound—all have a “song nuclei” in their brain: a group of interconnected neurons that synchronizes singing and learning. But the exact boundaries of that region are fuzzy; some researchers define it as larger or smaller than others do, depending on what criteria they use to outline the area. And differences between the song nuclei of parrots—which can better imitate complex sounds—and other birds are hard to pinpoint.
Neurobiologist Erich Jarvis of Duke University in Durham, North Carolina, was studying the activation of PVALB—a gene that had been previously found in songbirds—within the brains of parrots when he noticed something strange. Stained sections of deceased parrot brains revealed that the gene was turned on at distinct levels within two distinct areas of what he thought was the song nuclei of the birds’ brains. Sometimes, the gene was activated in a spherical central core of the nuclei. But other times, it was only active in an outer shell of cells surrounding that core.
When he and collaborators looked more closely, they found that the inner core and the outer shell—like the chocolate and surrounding candy shell of an M&M—varied in many more ways as well. Whereas the inner core of the parrot song nuclei resembled the complete song nuclei of other birds, the additional outer shell showed different patterns of activity in many ways. It also connected to the rest of the brain in different ways than the core and contained cells that looked different under the microscope.
“I was surprised,” Jarvis says. “I think bird brains are definitely understudied, but they’ve been studied enough that we should have recognized this region before.”
Jarvis's group went on to find the shell region in the brains of nine different parrot species, but not in songbirds or hummingbirds, which are poorer at imitation. And the better at imitating a parrot species is considered, the larger the shell region was, the researchers report today in PLOS ONE. Moreover, even keas (Nestor notabilis), which are more distantly related to other parrots, have a limited shell song region, suggesting that the shell appeared in parrot ancestors at least 29 million years ago.
“We think that the shells evolved as a mechanism for more complex vocal imitation,” Jarvis says. Parrots’ imitation abilities—in addition to providing party tricks for bird owners—are thought to be required for the birds to communicate with one another in the wild—to mate, pass along alarms, defend territory, or identify one another. Jarvis suspects the shell may have originally began evolving when the song nuclei, which is like that of songbirds, completely duplicated within the brain, and then began evolving new functions. If this hypothesis holds true, future studies on the parrot vocal shell could give key insight into the origins of such brain duplications—which have been hypothesized to occur in the past and could explain complex areas of the brain in humans and other animals.
But more work is first needed to precisely define the shell, says behavioral neuroscientist Claudio Mello of Oregon Health & Science University in Portland, who was not involved in the study. “It’s easy to see where the core ends, and that there are some domains beyond it,” he says. “But where exactly the shell ends, I would have a hard time telling you right now.”
Jarvis says he and his colleagues are planning more studies to test whether this brain region is indeed what allows parrots’ mimicry; so far, they’ve shown correlation but not causation. “I think we’ve found a primary reason as to why parrots have better imitation ability than other vocal learning species, and it’s because of this shell region,” he says. “But there are going to have to be more studies to validate this.”
(Video credit: Courtesy of Judy Bolton)