Does your first language affect the structure of your brain?

There are some differences between the brains of German speakers and Arabic speakers. Why do those differences arise? It seems to be because these 2 languages place different processing demands on some parts of the brain. Those conclusions emerge from a recent paper Native language differences in the structural connectome of the human brain, by Xuehu Wei, Helyne Adamson, Matthias Schwendemann, Tomás Goucha, Angela D. Friederici, Alfred Anwander, published in the journal NeuroImage, Volume 270, 15 April 2023

The paper is available on open access at Native language differences in the structural connectome of the human brain – ScienceDirect
A brief summary is available at Our native language shapes the brain wiring | Max-Planck-Gesellschaft (mpg.de)

What did the research find?

The researchers found that:

  • People who learnt German as their 1st language show stronger connectivity in areas of the brain believed to be used in processing complex syntax.  
  • Native who learnt Arabic as their 1st language show stronger connectivity between the left and right halves of the brain.

picture: Creative Commons license

The researchers suggest that these differences arose because:

  • speakers of German need to process complex syntax, involving inflectional morphology and word order is much less fixed than in Arabic.
  • speakers of Arabic need to process that language’s system of roots (typically made up of 3 consonants), that need to be integrated with patterns of vowel (and some prefixes and suffixes). Performing this integration appears to draw together information from both halves of the brain.  

Example of Arabic roots and patterns
A single root k-t-b has the general meaning of ‘write’. It combines with:
– the pattern -a-a-tu {fa3altu} to form katabtu (‘I wrote’)
– the pattern -o-u-o {fo3ulo} to form kotub (‘books’)
-the pattern -ā-i- {fā3il} to form kātib (‘writer’)
– the prefixed pattern ma–a- {maf3al} to form maktab (‘office’)
In depicting those patterns, the letters <f>, <3>, and <l> are placeholders indicating where the root’s 1st, 2nd and 3rd letters are inserted, respectively.

One caveat

There are some differences between the sound systems of the 2 languages. For example:

  • German (but not Arabic) has the sounds /p/, /g/, /ç/
  • Arabic (but not German) has the emphatic sounds /ħ/ and /ʕ/.

The authors say further research is needed to assess whether those differences in sound systems cause any of the differences in brain structure they found.

Effect of writing systems

The authors also suggest that 2 differences in writing systems may contribute to differences found by the study:

  • Arabic writing does not generally show vowels, so the reader must rely on context or prior linguistic knowledge to infer a word’s meaning. This requires greater use of the right hemisphere. Perhaps this partly explains why Arabic readers show similar levels of activation in both hemispheres. On the other hand, activation in German readers is stronger in the left hemisphere.
  • Arabic is written from right to left. So, Arabic readers apparently make greater use of those areas of the right hemisphere involved in spatial cognition. It seems they have developed stronger channels to transfer spatial information from the right hemisphere to the left hemisphere. This writing system may require transfer of more information from the left visual field (processed in the right hemisphere), to the left hemisphere, where most language processing happens.

What did the research involve?

The study carried out MRI (magnetic resonance imaging) scans on 47 native speakers of German and 47 native speakers of the Levantine dialect of Arabic. All participants were healthy young adults, speaking only one native language. They were all right-handed and had similar levels of education.

The Arabic speakers had arrived in Germany 6–8 months before the start of the study. They had settled in Leipzig for a long-term stay and to learn German, but knew little or no German. They had above average intelligence and no clear symptoms of mental health problems or post-traumatic stress disorder. 

Final comments

This study produces some intriguing evidence that the nature of someone’s first language determines (partly) the structure of some parts of their brain. This is because different languages place different processing demands on different parts of the brain. Thus, some pathways in the brain become more developed if they are more heavily involved in language.

This research looked at 1st language acquisition, not at 2nd language learning. But the paper makes an interesting comment. Prior work has shown that, during 1st language acquisition in childhood, the brain’s structure changes in a way that differs how it changes during later 2nd language learning. Processing a 2nd language learned in adulthood does not use the native language system and may involve other brain areas, for example to perform additional tasks such as language switching and cognitive control. I assume this is also because the process of acquiring a 1st language differs greatly from the process of learning a 2nd language.

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