How does our brain go about learning a new language in adulthood? A study of epilepsy patients has now given researchers insights into how the brain manages the task of learning new sound systems without impairing existing language skills. A neural fine-tuning is emerging, which is connected with the balance between plasticity and stability. Thus, an individual tendency towards greater stability in the head could be associated with greater language learning difficulties.
Learning a foreign language in adulthood is known to be difficult and the respective talents vary from person to person. But why? When answering this question, it makes sense to first take a look at the basics: During the learning process, we initially familiarize ourselves with the new sounds, which, depending on the type of language, differ to a greater or lesser extent from the speech sounds we are already familiar with. “Familiarization is a crucial step in learning a language – but so far this phase has hardly been explored. As part of our study, we have therefore now shed light on what happens in the brain regions that are involved in the differentiation of sounds in this initial phase of learning, “says senior author Matthew Leonard from the University of California in San Francisco.
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Epilepsy patients support brain research
The researchers were given the insights into ten adult epilepsy patients who had been implanted with electrodes in their brains as part of their treatment to locate the source of their seizures. These sensors enabled the scientists to record in detail the activity of certain groups of nerves in different areas of the brains of the study participants. The focus was on an area of the brain, the importance of which is known in language ability. The aim of the scientists was now to record how neural activity changes as a person becomes familiar with the sounds of a foreign language.
The test persons, whose mother tongue is English, were confronted with spoken sounds of the Chinese language Mandarin. This presents a particular challenge because it is a tonal language: the meaning of a word depends not only on the vowel and consonant sounds, but also on subtle changes in the pitch of the voice. The syllable “ma”, for example, has a different meaning depending on whether it is pronounced with a rising or falling tone. It is difficult for speakers of non-tonal languages such as English to correctly grasp these unfamiliar sounds.
For the study, the test subjects were asked to recognize in recordings of different Mandarin speakers how they were pronouncing a certain syllable: After each listening impression, they stated whether they believed that the tone rises, falls or remains the same, and received feedback as to whether they were right. Patients repeated this task about 200 times over several five- to ten-minute sessions. As a result, they practiced categorizing the tones – although there were fluctuations in performance, the researchers report: “Often a series of experiments were mastered well by the test persons, then they began to be more wrong, and then they did it again right – a kind of up and down that seems to be part of the learning process, ”says Leonard.
Fine-tuning process
As the researchers explain, this variation in performance could be related to the results of their neural evaluation. Accordingly, a surprising pattern emerged in the fundamental learning process of the foreign sound system. Previously, it was thought that activity throughout the language cortex increased when a person was dealing with a language that he or she was becoming increasingly familiar with. Instead, the scientists discovered a spectrum of changes in this area of the brain, with activity in response to certain spoken auditory impressions increasing in some parts while decreasing in others. “It’s like small groups of neurons taking on different roles,” says lead author Han Yi from the University of California at San Francisco. A carefully balanced equilibrium appears to be established: “These neural units all communicated with one another in order to reach the point at which they can correctly carry out the task by working together,” says Leonard.
The scientists see a pattern in this that has to do with the “balancing act” in learning something new: our brain must reconcile neuroplasticity – the ability to make new connections between neurons when learning new things – with the stability that enables us to keep the integrated networks of things already learned. “When we learn a new language, our brain has to somehow reconcile both, while the requirements compete with each other. This makes it possible to learn the Mandarin tone system without affecting the ability to perceive the pitch in English or in music, ”says Leonard. The neuronal traces of fine-tuning that have now been revealed seem to be linked to this compromise, the researchers explain.
According to them, the results also provide information about the background to the different linguistic abilities of people. Their results made it clear that the neural processes involved in becoming familiar with the new sound system differ from person to person. Some people learn new sounds more easily than others because each individual brain finds its own balance between maintaining the stability of the mother tongue and the plasticity required to learn a new language. “It seems like each person’s brain has a unique set of knobs that are fine-tuned as they become familiar with new tones,” says Leonard.