Parrot fashion: Understanding Monty's mate

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  • Published: Jul 1, 2015
  • Author: David Bradley
  • Channels: MRI Spectroscopy
thumbnail image: Parrot fashion: Understanding Monty's mate

Pertinent parrot

Gene expression imaging has been used to reveal the structural differences in the parrot brain that could explain why these birds are such good mimics. The discovery marks a turning point in almost three and a half decades of research and could lead to new insights into the neural  mechanisms of speech in humans too. (Credit: Courtesy of Jonathan E. Lee, Duke University)

Specialized and behaviorally regulated gene expression has been used to reveal the structural differences in the parrot brain that could explain why these birds are such good mimics. The discovery marks a turning point in almost three and a half decades of research and could lead to new insights into the neural mechanisms of speech in humans too.

An international research team led by Duke University scientists Mukta Chakraborty and Erich Jarvis includes collaborators Solveig Walløe and Torben Dabelsteen of the University of Copenhagen, Denmark; Signe Nedergaard, now at the National Centre of Forensic Services in Vanloese, Denmark; Emma Fridel of Duke, Bente Pakkenberg of Bispebjerg University Hospital, Copenhagen, Mads Bertelsen of the Copenhagen Zoo in Frederiksberg, Gerry Dorrestein of the Dutch Research Institute of Avian and Exotic Animals in Veldhoven, Netherlands, Steven Brauth of the University of Maryland, and Sarah Durand of LaGuardia Community College in New York.

"This finding opens up a huge avenue of research in parrots, in trying to understand how parrots are processing the information necessary to copy novel sounds and what are the mechanisms that underlie imitation of human speech sounds," explains Chakraborty. Parrots are one of only a few animals that are "vocal learners" with the ability to imitate sounds that they hear. For decades, scientists have puzzled over why some birds are better than others at the imitation game Differences in the sizes of specific regions of the brain have not led to particularly fruitful explanations. Jarvis told us that, "Behaviourally, gene expression profiles we identify is analogous to those profiles seen in the brain by functional magnetic resonance imaging (fMRI)."

Just an expression

Now, by investigating gene expression patterns, the international team has demonstrated that there are structural differences in the parrot brain not seen in species of songbird and hummingbird that also have some vocal learning skills. All three groups have the so-called "cores", centres for vocal learning but parrots also have what the team refers to as "shells" outer rings that also appear to be involvedin vocal learning. In addition, these shells are much bigger in species of parrots that are well known for their ability to imitate human speech, the group reports in the journal Plos One.

Until now, the budgerigar (common pet parakeet, Melopsittacus undulatus) was the only species of parrot whose brain had been probed for the mechanisms of vocal learning, which was included in this study. The team also characterized parrot brain tissue from eight other species provided by the researchers in Denmark and Netherlands, including conures, cockatiels, lovebirds, two species of Amazon parrots, a blue and gold macaw, a kea and an African Grey parrot. The team looked for specific gene markers that were known to have specialized activity in the brains of humans and song-learning birds. The resulting gene expression patterns in all parrot brains were correlated with neural tracing experiments in budgerigars.

The team found that even the oldest parrot, evolutionarily speaking, the New Zealand kea possesses the shell structures, although these are more rudimentary than those present in "younger" species. This, the team suggests, implies that the populations of neurons in the shells probably arose at least 29 million years ago. Until this study, scientists had assumed that the regions surrounding the cores had nothing to do with vocal learning.

Conflict resolution

Indeed, a study in the year 2000 by Jarvis and Claudio Mello of Oregon Health & Science University seemed to show that the core and shell were simply parts of one large structure. This conflict led to some confusion in the field about the relative importance of different parts of the parrot brain in vocal learning. Jarvis teamed up with Maryland's Brauth and former postdoc Durand in order reconcile the evidence.

"The first thing that surprised me when Mukta and I were looking at the new results is, 'Wow, how did I miss this all these years? How did everybody else miss this all these years?'' says Jarvis. "The surprise to me was more about human psychology and what we look for and how biased we are in what we look for. Once you see it, it's obvious. I have these brain sections from 15 years ago, and now I can see it," he adds.

The new paper supports the hypothesis that in humans and other song-learning animals, the ability to imitate arose by brain pathway duplication. How such a copy-and-paste job could have happened is still unknown. "How can you get a mirrored song system surrounding another one?" Jarvis asks. "Each (vocal learning centre) has a core and a shell in the parrot, suggesting that the whole pathway has been duplicated." Most of the bird's vocal learning brain regions are tucked into areas that also control movement. These areas in parrots also show some special patterns of gene expression. The team has speculated that this also explains why some parrots can learn to "dance" to music.

'It takes significant brain power to process auditory information and produce the movements necessary for mimicking sounds of another species,' Chakraborty adds. "The question is, how specialized are these parrot brains, and in what ways? Is it just a select group of specialized genes, or is it some specific projections that we haven't discovered yet?"

Of wider importance is the question of whether or not the shells give parrots a greater ability to imitate human speech. "If that's true, then we've answered a big question in our field that people have been wanting to know for many years," Jarvis says.

Related Links

Plos One 2015, online: "Core and Shell Song Systems Unique to the Parrot Brain"

Article by David Bradley

The views represented in this article are solely those of the author and do not necessarily represent those of John Wiley and Sons, Ltd.

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