How the brain learns new languages
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We know that the acquisition of our mother tongue cooccurs with the maturation of the language network in the brain. This universal language network is structurally and functionally specialized for language processing, and can be modulated by the specific processing demands of one’s native language. One of the fundamental questions in cognitive neuroscience is whether our brain can be reshaped by newly acquired languages even after the neural system reaches a mature state. Current evidence suggests this may be possible.
By Xuehu Wei
The brain is an adaptable organ that exhibits experience-dependent plasticity during development – and while it is the basis of cognition, it can also be shaped by newly acquired knowledge. One of the most remarkable cognitive abilities of humans is language. Language is not only a tool for human communication but also a bridge between the mind and the world. Our brain and cognitive functions develop in parallel. We know that as infants and children develop the language faculty, an elaborate and extensive language processing system is shaped in the human brain. This is the universal neural network for language, that is similar across individuals and specialized for language processing. It consists of the regions located in the frontal, temporal and parietal cortical region of the left hemisphere and to some extent the parietal and temporal cortices of the right hemisphere, as well as the white matter fiber pathways connecting these regions.
Although all languages build on this universal system, some degree of variability can occur. Brain activation patterns can vary according to the language being spoken and brain connectivity can differ between different native language speakers. For example, when a German native speaker hears “Wie geht es Ihnen?” or an English native speaker hears “How are you doing?” neural activity occurs predominantly in the left hemispheric language regions, while when a Chinese native speaker hears “你好吗?” or an Arabic native speaker hears “ كيف حالك”, additional activity occurs in the right hemisphere’s temporal cortices. Beside the activity pattern difference, the structural character of the language network also shows significant difference between different native speaker’s brain. In one of our studies, we found that, compared to Arabic native speakers, German native speakers have stronger connectivity in the left frontal-parietal-temporal language network, associated with complex syntax processing. In contrast, Arabic native speakers showed stronger connectivity of the inter-hemispheric and left temporo-parietal network connecting semantic language regions. Since Arabic is a language with rich lexical morphology, the stronger connectivity between semantic language regions may contribute to the rich morphological processing in Arabic. Suggesting that different orthographic, phonetic, and semantic characteristics of each language can impact experience-dependent brain plasticity, resulting in differences in the structural and functional consequences for the mature language system.
As the brain matures, the nervous system becomes relatively stable, and a functionally specialized native language (L1) network is formed by adulthood. However, this doesn’t mean that the brain’s capacity for experience-dependent change is over. To take an analogy, if we consider the adult brain as a ball with a more or less fixed round shape, it would be a highly flexible plastic ball that could continually change when bounced, squeezed, or inflated – except, instead of being bounced, squeezed, or inflated, the brain is being excited or inhibited by experiences and its neural connections are growing or shrinking. Connections between neurons (nerve cells) strengthen and weaken in response to new experiences continually throughout the lifespan. Therefore, in adulthood, brains retain the neuroplasticity to undergo reorganization during second language (L2) learning to accommodate a new language.
As a next step, it is important to understand if and how L2 learning reshapes the structural connectivity between different brain areas. Previous studies have shown that learning a new language changes cortical properties and structural connectivity along the right frontal-parietal-temporal system in addition to changes in the left language network . These structural alterations are thought to contribute to successful processing of novel speech sounds, new vocabulary, and new syntactic rules. Changes in gray matter (which is consists primarily of cell body, the outer cortex of the brain) could reflect new memories for second language knowledge. The brain changes in the cortical regions (gray matter) and in the structural connectivity between regions (white matter) induced by adult L2 learning differ from the brain’s natural development under L1 acquisition. These processing differences are reflected in previous structural studies of L2 acquisition in adults showing changes in the white and gray matter of the brain extending to areas not involved in L1 processing. For example, L2 processing has shown right-hemispheric involvement, in particular in the early stages of learning. So that, L2 learners showed an increased connectivity of the frontal-parietal-temporal pathways in the right hemisphere after several months of L2 training. At the same time, L2 learning might also modified the white matter connections between the two hemispheres. Second language learning in adulthood may involve additional processing tasks such as language switching and cognitive control. This additional cognitive processing could lead to complex reorganization in cortical and sub-cortical areas. All those changes in these additional areas can help learners deal with new languages more efficiently.
We can compare the brain to a central processing unit (CPU) in a computer. The brain can be thought of as a “plastic and functionally specialized” version of a CPU, meaning that it is capable of adapting and changing in response to experiences (plasticity) and has specialized areas that are responsible for specific functions (functionally specialized). In this context, the language network is a subsystem within the brain, built by a set of registers (temporary storage areas) and control units (parts of a computer’s CPU that manage the flow of data). The number of registers and control units need to be activated, as well as the activity logic for each response, depend on the characteristics of the input and output signals. In contrast to the “CPU” in computers, which have a fixed number of physical units that are pre-set, the human brain continuously exhibits experience-dependent plasticity throughout a person’s lifespan.
It is worth noting that the neural mechanisms underlying language learning are complex, because the configuration and reconfiguration in brain networks by L2 experience depend on a variety of variables, including the linguistic features and similarities of the two languages, the age of acquisition, the extent of the learning experience, the context and method of learning etc. The recent L2-related studies only reflect the tip of the iceberg. However, it’s clear that the languages we acquire throughout life can reshape our brains, and those changes not only support better processing of new language tasks itself, they also boosts other skills (a more powerful memory, more creativity, improved concentration). So, keep on learning, exercising your brain.