What our speech and the song of the thrush have in common – basic science

from Tarciso Velho

Songbirds help us understand stuttering and other language disorders

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In general, we start speaking naturally. We imitate what we hear from parents, friends, whoever is around. That is, we modify the utterances according to what we hear. We learn, we make mistakes, we rehearse again. And this is how a communication system, the spoken language, is unique in the animal world. It is unique, universal, a biological characteristic of us.

However, a select group of animals share with us what we call vocal learning: they learn by listening to and copying other animals of the species. To the surprise of some, this group does not include the large primates but other animals: aquatic mammals (whales, dolphins, pinnipeds), bats, birds and possibly elephants and the common marmoset. However, not all birds learn their utterances, only songbirds, hummingbirds and parrots

But why do we care? Because such a special biological process as vocal learning has to be examined meticulously. Be it to better understand language disorders or to satisfy our curiosity.

For example, about 5% of American children have some form of speech impairment, of which 20% stutter. The cause of most of them is unknown. In addition, estimates suggest that around 40% of children diagnosed with autism, the causes of which are largely unknown, are considered nonverbal.

It is therefore important to understand the neurobiological basis of language acquisition and the genetic components involved in it. Until then, human studies helped to understand the process and carefully characterize the stages of language acquisition. Rare genetic mutations have been shown to be linked to defects in learning and language production, including persistent stuttering and apraxia, but it is not yet fully understood how these mutations affect brain function. It is also important to emphasize that the environment influences learning so much that we learn different languages, develop regional accents, build our vocabulary based on educational level, etc. However, it is not yet clear how the environment affects the function of the language involved circuits in the brain or whether and which environmental factors contribute to language disorders.

For the past fifty years, songbirds have been the subject of a search for the neurobiological basis of vocal learning. They also start singing while listening to their adult peers. They learn, make mistakes, rehearse again. So much so that the choke on your street has a different corner from the one on the street below. São Paulo Drossel likely has a different dialect than gauchos. And this is a direct product of the learning process and the model used.

Humans and songbirds need their hearing to be intact in order to learn and maintain vocalizations – children with hearing problems have language learning difficulties. Hearing loss in adults leads to deterioration in speech, such as changes in intonation and rhythm.

Birds, like us, have a critical learning phase when the brain is particularly sensitive and efficient at learning a language (or two or three). Then this capacity drops drastically and over time we become more and more limited. That is why so many of us find it difficult to face a second language in adulthood. Although we are fluent in a second language, we still speak with an accent. And this accent has a sensory origin: when we are exposed to the mother tongue, we cease to perceive noises that are not common to it. We cannot reproduce certain sounds of the second language because we cannot perceive these sounds. Our hearing aids suffered from neural impairment, a condition that birds share.

Despite tremendous advances over the past few decades, we know little about the genetic basis of this process. Which genes are important? Are there those who are exclusively involved in vocal learning, or are we looking for generic genes and language is just one of the many characteristics that emerge from the brain? We don’t have the answers yet, but from animal models like songbirds and their genetic manipulation, we will surely have them.

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Tarciso Velho is a neuroscientist and professor at the Federal University of Rio Grande do Norte.

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