Humans possess the ability to master multiple languages simultaneously. This ability is especially strong in the early ages of development and leads to structural and functional changes in many brain areas associated with language acquisition. Understanding how the brain accommodates multiple languages simultaneously is crucial to developing a complete picture of our species’ linguistic capabilities (Marian et al., 2017).
In one study, Dr. Berken and colleagues seek to understand how language experience timing shapes the function and structure of the brain through bilingualism. The paper reviewed evidence from previous studies that have used neuroimaging techniques like positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and structural MRI to examine optical periods in language development. The review particularly focused on differences in brain structure and function in early vs late experience of bilingualism attainment.
Three groups of participants’ (French–English bilinguals who acquired two languages from birth, French–English bilinguals who learned their L2 after the age of 5 years, and English-speaking monolinguals) neural activation were compared using fMRI during French and English oral sentence readings. The participant's language competency was then accessed using the language experience and proficiency questionnaire (Berken et al., 2017). Blood Oxygen Level-Dependent (BOLD) fMRI scans were obtained while participants read sentences aloud in French and English. Blocks of French and English sentences were presented in a predetermined order on a back-projected screen that participants viewed through a mirror mounted on the head coil
Results of the study provide evidence that there is an overlap of neural substrates engagement for two language processing when acquired from birth in a native context. The sensitive period of L2 acquisition limits the maturation of brain regions responsible for speech production and phonological encoding regardless of language proficiency.
In another study, Dr. Marian and colleagues examined the neural mechanisms involved in the processing of two languages by comparing cortical activation in Spanish-English bilinguals in response to between- versus within-language phonological competition. Participants of the study completed a spoken word recognition task while in a functional magnetic resonance imaging (fMRI) scanner, under four experimental conditions: English within-language (English target, English competitor), English between-language (English target, Spanish competitor), Spanish within-language (Spanish target, Spanish competitor), and Spanish between-language (Spanish target, English competitor). Neural responses to phonological competitors were compared to baseline trials where no phonological competitors were present (Marian et al., 2017).
Results of the study revealed that between-language competition recruited a larger network of frontal control and basal ganglia regions than the within-language competition. Bilinguals also recruited more neural resources to manage between-language competition from the dominant language compared to the competition from the less dominant language. Also, activation of the basal ganglia in bilinguals was inversely correlated with their respective executive function ability. This suggests that lower levels of cognitive control in bilinguals are compensated for the recruitment of a broader neural network to manage more difficult tasks. The results evident existing differences in neural responses to linguistic competition between and within languages, and demonstrate the brain’s remarkable plasticity, where language experience can change neural processing (Marian et al., 2017).
References
Berken, J. A., Gracco, V. L., & Klein, D. (2017). Early bilingualism, language attainment, and brain development. Neuropsychologia, 98, 220–227. https://doi.org/10.1016/j.neuropsychologia.2016.08.031
Marian, V., Bartolotti, J., Rochanavibhata, S., Bradley, K., & Hernandez, A. E. (2017). Bilingual cortical control of between- and within-language competition. Scientific Reports, 7(1). https://doi.org/10.1038/s41598-017-12116-w
Very interesting findings and a good read
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