Budgies' brain reveals the secrets of human speech

Several bird species are capable of imitating human speech. Some songbirds, corvids, and parrots also produce vocalizations to communicate. But how they do this and whether they do so in a similar way to humans has been a mystery. Now, a study with budgerigars published in Nature has begun to unravel the mystery: they have a series of neurons specifically dedicated to activating their vocal organs. Some of these neurons are so specialized that they control the intonation of their songs or the pitch of their calls. They accomplish this with a different part of their brain, but otherwise, the mechanism is the same as in humans.

“Parrots, like the budgerigars featured in this study, are known for their incredible vocal ability. They can mimic a variety of environmental sounds, including speech,” said Michael Long, senior author of the paper and a professor at the University of New York Medical School, in an email. “We discovered that there was a representation of vocal sounds in the part of the brain analogous to a key speech production center in humans. This is the first non-human species in which such a vocal motor map has been observed.”

The researchers' discovery goes even further: through spectral analysis, they confirmed a correlation between the type of vocalization and the pattern of brain activity. For example, a chirp with a specific pitch, whether higher or lower, was accompanied by the firing of certain neurons, but not others. In humans, the part of the motor cortex dedicated to speech encodes pitch — the frequency of the vocalization. In budgerigars, this area of the brain modulates pitch by controlling the tension in the walls of the syrinx.

For Zetian Yang, the lead author of the research, there is a correlation between the type of sound a budgie produces and the type of neurons that are activated. When asked about other species related to budgies, Yang acknowledges that this has not been researched, but believes that “parrots with similar vocal abilities could share the same neuronal organization.”

People can speak, sing, shout, or whisper thanks to a series of neurons in the motor region of the cerebral cortex that extend their nerve endings to the brain stem, a crucial highway connecting the brain to the spinal cord and the rest of the nervous system. Here, these nerve endings reach the ambiguous nucleus, which controls the muscles of the mouth, pharynx, and, notably, the larynx, the human vocal organ.

Birds, however, have a different brain structure, as well as different vocal anatomy. They lack vocal cords and instead produce their songs with the syrinx and the vibrations of its walls. Studies with parakeets that were unable to sing revealed that their ability to vocalize was linked to a homolog of the cerebral cortex in mammals, known as the anterior arcopallian nucleus (AAC). Electrical stimulation of this area innervated the syrinx, restoring the birds’ ability to sing.

Building on this, neurologists at New York University Langone Medical Center in the United States placed tiny devices in the heads of several budgerigars. Over multiple sessions, they recorded more than a thousand trills and dozens of calls from four males (the ones in the image). They observed how certain neurons in the AAC were activated and how their nerve endings reached the syrinx through the brain stem. To ensure that this activity was not originating from another source, they also recorded the birds while they listened to the trills of other budgerigars and during moments of silence. Additionally, they noted how the same neuronal groups were reused when the birds produced very similar sounds.

Joshua Neunuebel, a neuroscientist at the University of Delaware in the United States, also wrote a commentary in Nature discussing the implications of the study with these parakeets. He begins by highlighting the differences between the species: “Humans possess unmatched vocal flexibility for speech, parrots excel at imitation, and zebra finches [used as a control group in the study] produce stereotyped songs with fixed syllables.” Even so, he emphasizes what they have in common. Despite the anatomical differences, “the fundamental neuronal organization from the forebrain, through the brain stem, to the vocal organ is maintained, demonstrating how similar architectures have adapted throughout evolution to produce unique vocal behaviors.”

Understanding human speech

This idea of evolutionary convergence from different perspectives was demonstrated by the recent publication of several studies on the brains of mammals, birds, and reptiles. Fernando García Moreno, an Ikerbasque researcher at the Achucarro Basque Center for Neuroscience and lead author of two of these studies, explains this process: “Parrots can imitate our way of speaking, but their brains control vocalization with different parts of the brain than humans. While humans use the neocortex, parakeets do so through the anterior nucleus of the arcopallium, a region evolutionarily related to the amygdala in the human brain.”

For García Moreno, the similarity of vocal circuits is surprising, despite the distinct brain components. His work, published in Science, found that neurons and circuits in hierarchically higher brain regions evolved independently in mammals and birds, but converged on similar functions. This study, he adds, “shows that even though they evolve independently, the physiology of speech is very similar in the two species groups; therefore, the biological basis of speech can be understood equally in parakeets and humans.” “Studying these small parrots could help us better understand vocal production in humans, both in normal speech and in related disorders,” he concludes.

That’s one of the final ideas the authors of the budgie study offer: using them to better understand human speech and the disorders that prevent some from speaking. The other is the dream of understanding what they convey in their trills.

In the future, Dr. Long says, “we would like to use advanced machine learning methods to translate the sounds budgies make into objects or actions.” “We’re interested in the cognitive processes that allow them to access specific sounds; these processes are similar to those that allow us to think of a word, and these calculations fail in communication disorders like aphasia,” he concludes.

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