How our first language shapes brain’s connectivity structure

connectivity
Author: Juan F. Trillo, PhD in Linguistics and Philosophy (U. Autónoma de Madrid), PhD in Literary Studies (U. Complutense de Madrid).

The plasticity of the brain and its ability to adapt to the most diverse requirements and demands, such as the use of a specific language, has been well known for years ¹² . This is a field in which there is an abundance of research, especially from the last three decades. It is known, for example, that the different directions in which Semitic and Indo-European language texts are read reflect in spatial cognition. To read the texts of the former, the brain would activate both the left and right hemispheres, something that does not happen in the case of the latter, which would use mainly the left hemisphere ³⁴ .

More recent work has been deepening our understanding of the effects that different languages have on brain structure and connectivity. Along these lines, a team from the Max Planck Institute for Human Cognitive and Brain Sciences, in Leipzig, Germany, has recently published the results of their research ⁵ , in which they reveal a strong and particular structural connectivity of the neurolinguistic network, depending on the language spoken by the subjects under examination. Previous studies had established the existence of syntactic, semantic and phonological networks, which seemed to form a universal linguistic neural network ⁶. The effect of cultural and linguistic differences on brain functions was also known, but the question remained as to how this would be physically reflected in the brain structure, and the aim of the research team was precisely to verify to what extent the acquisition of a given language as L1 contributes to the formation of these structures.

The research team led by Xuehu Wei focused on 94 monolingual adult speakers of German and Arabic, aged 18-34, hypothesizing that the use of each of these two languages would be reflected in neural networks involving different areas of the brain. If that were the case, it seems logical to assume that, in the long term, the effects of the particular characteristics of these very different languages would be reflected in specific neural networks.

To verify this, high-resolution images of the brain were taken using the 3-Tesla magnetic resonance imaging system, while the researchers used probabilistic tractography to elaborate the structural connectivity networks.

The chosen languages have very different grammatical characteristics, each coming from a completely separate language family, Indo-European in the case of German and Semitic in the case of Arabic. The syntactic structure of Arabic, for example, is limited in most cases to subject-verb-object, whereas that of German is considerably more flexible. In German, on the other hand, the greater freedom in word order is usually accompanied by a number of morphological marks —in the form of suffixes and prefixes— which provide the necessary information for extracting meaning from the verbal production.

As the researchers had supposed, the language with a more complex syntax —in this case German— is associated with greater frontal lobe connectivity with the posterior temporal lobe, something that had already been detected by researchers such as ⁷ or ⁸. On the other hand, the rich morphology of Arabic would be responsible for the connections observed in these speakers between the temporal and parietal lobes. Both groups showed a marked left lateralization, confirming on the one hand the widespread belief that it is this hemisphere which deals with linguistic processing ⁹, and on the other hand, that this is a universal phenomenon.

In essence, the result corroborates that external factors —as in this case, the mother tongue of each speaker— have a decisive influence on the physical configuration of the brain, more specifically on the structure of the linguistic connectome. In this sense, the brains of newborns would be like the traditional blank slate, an organ with an enormous potential to develop connections and neural networks determined by the speaker’s L1. The anatomical differences and therefore the asymmetries between the brain lobes would be a consequence, among other reasons, of the demands to perform certain specialized tasks, in this case linguistic processing.

Whether or not the articulatory differences between the two languages are responsible for certain differences observed in the brains of the speakers remains to be elucidated, however, and further research is needed in this regard. The Max Planck Institute team intends to continue its studies along the same lines, also looking at the new connections developed in Arabic speakers who start learning German at an adult age.

Work such as this one contributes to a more precise “linguistic map” of the brain, determining which areas of the brain and which neural networks are involved in reading and listening comprehension, as well as in verbal and written production, and of course how different languages influence the aforementioned linguistic map.