Exposure to speech before birth can facilitate learning in newborns

Babies pick up language quickly, much faster than adults. A few months are all they need to begin to understand basic words; after a year, they are already articulating words. Scientists have even suggested that the acquisition of language begins before birth, because a fetus can already hear after six or seven months of gestation, and newborns prefer their mother’s voice over other female voices. Now, research published this week in the journal Science Advances suggests that speech stimulation through the mother’s voice in prenatal stages produces changes in the baby’s neuronal activity that contribute to the learning of language processing: before birth, the baby’s brain begins to be modeled, from these first experiences with language, to understand its native language.

In the final stages of pregnancy, the fetus can hear muffled sounds from outside. The uterus acts as a kind of filter that attenuates frequencies above 600 hertz: individual sounds are suppressed, and only the melody and rhythm of speech remain. Enough, in any case, for newborns to prefer their mother’s voice over others, and to lean towards the language that she spoke during pregnancy.

What was not known until now is how the brains of children were shaped by those first linguistic experiences, and whether this prenatal exposure could improve their ability to learn a language in the first stages of life. “It was still not clear how much babies learn from prenatal experience,” admits the author of the study, Judit Gervain, a researcher at the Center for Neuroscience of the University of Padua (Italy). “Previous studies, including studies from our own laboratory, had shown that this filtered prenatal experience shapes the baby’s ability to perceive speech and shapes brain mechanisms related to language. What is new about our study is that we show learning as it develops. We discovered that the activity of a newborn’s brain is transformed in real time, even after a few minutes of listening to people talk in their native language, that is, the language they heard before birth,” she explains.

The researchers analyzed, through encephalography, the neuronal activity of 33 newborns of French-speaking mothers. They placed caps with a dozen electrodes located near brain areas associated with auditory and speech perception, and monitored their activity. First, they measured resting-state activity for three minutes. The babies then listened to speech in three different languages: French, Spanish and English, in seven-minute blocks. Finally, resting-state activity was measured again for three minutes. “The speech stimuli consisted of natural recordings of translation equivalent sentences in the three languages from the children’s story Goldilocks and the Three Bears recorded in mild infant-directed speech,” explain the researchers.

By comparing resting states with cycles of linguistic stimulation, the researchers wanted to find out whether language exposure affects neural dynamics in the infant brain. “Plastic changes immediately following exposure to speech may underlie infants’ ability to learn about the sound patterns they hear,” they write. “We asked whether exposure to speech makes lasting changes in neural dynamics, supporting learning and memory.” They also wanted to see whether these plastic changes take place in the brain after exposure to all languages, or only to the language heard prenatally; that is, if prenatal experience already shapes, in some way, neural circuitry. “If prenatal experience already plays a role, then newborns may show greater plastic changes after exposure to the language heard prenatally than after unfamiliar languages,” the researchers continue.

After conducting the studies, the scientists concluded that “newborns’ electrophysiological activity exhibits increased long-range temporal correlations [LRTCs] after stimulation with speech, particularly in the prenatally heard language, indicating the early emergence of brain specialization for the native language.” LRTCs are a unit of measurement that indicates “how similar a signal, in this case that of brain activity, is to itself on large time scales,” explains Gervain. “We found that after stimulation with the native language, babies’ brain activity is more similar to their previous states than before stimulation. This is, therefore, a sign of learning,” says the scientist.

Thus, what happens when newborns are exposed to their mother’s language is that their brain activity becomes organized in such a way that the activity repeats or resembles itself over long periods of time. “We could say that it retains a certain type of memory of its own responses to previous events, and those same responses become more frequent,” Gervain explains. The experience of language in prenatal stages can therefore begin to shape the brain and contribute to learning. “The results show that for French, the language heard prenatally, brain activity shows more ‘memory’ of previous states, but not for two unfamiliar languages. This shows the learning of the language heard before birth,” says Gervain.

Non-deterministic impact

The researchers explain that, while their findings suggest that the prenatal period lays the foundations for further language development, “its impact is not deterministic.” This means, says Gervain, “that it helps and supports the learning of the same language. However, if the prenatally heard language is not the one the baby will learn after birth, due to adoption or moving, for example, having no prenatal experience does not have a strong detrimental effect. Newborns can learn languages to which they were not exposed prenatally in the usual, normal way.”

Jordi Costa Faidella, researcher at the Institute of Neurosciences of the University of Barcelona and the Sant Joan de Déu Research Institute, thinks that this study “adds evidence to a booming field, that which investigates the effects of prenatal exposure to auditory stimuli produced by the mother or environmental sound.” What is most innovative about it, he continues, is the methodology that was used. “What this study provides is this idea that the learning with which the baby is born is quite specific: the baby’s brain activity is in tune with the mother’s language, the brain rhythms adjust to the mother’s rhythms.” The scientist points out that this study (in which he did not participate) opens possibilities for early interventions in babies at risk of developing language acquisition problems: “If plastic changes are already generated from the womb due to this exposure, perhaps interventions can be made earlier in babies born at risk for future language-related problems. For example, babies with low birth weight or high birth weight, which may be more likely to suffer some delay in language acquisition,” he suggests.

In any case, the importance of exposure to language is now recognized as a key element in neurodevelopment. In the neonatology unit of the Vall d’Hebron Hospital, in Barcelona, Spain, where premature children are treated, they often use voices as a neurostimulation tool. “Especially the mother’s voice. We try to stimulate them with her voice when they are in the incubator,” says neonatologist Fátima Camba. They are aware of how important it is that these premature babies, outside the uterus before their time, are exposed to voice and language. This is key to their neurodevelopment, the doctor points out. “When a baby is born prematurely, we try to make their development as similar as what life inside the womb would be, because we know that the external stimuli they receive are inappropriate for them and can have a negative effect. Thus, when a baby is born prematurely, we try to simulate the environment of the womb and look for a quiet environment, where the mother speaks to them in a way that is similar to what they would hear inside the womb,” she concludes.

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