“Depending on the type of grammar used in forming a given sentence, the brain will activate a certain set of regions to process it, like a carpenter digging through a toolbox to pick a group of tools to accomplish the various basic components that comprise a complex task” (1). This was the descriptive offered by one review on how it is that diverse regions of the human brain are recruited to tease out the meaning of sentences when we communicate with each other (1). Cutting edge research into brain function, using American Sign Language as a platform, has unpacked the detail of exactly how the brain achieves this split-second feat (1,2).
In sign language messages can be expressed in one of two ways. As with English, ‘signers’ can use ordered words to convey their message (eg., John gives his lunch to Mary). But they can also move their hands in a manner that specifically relays concepts and ideas- what linguists call ‘inflection’ (2). In languages such as German and French inflections are easily identifiable as suffixes that can be tagged onto the ends of words to denote, amongst other things, the case or the gender of the word or the ‘role’ that a subject or object in a sentence plays in a given interaction (John giving lunch to Mary in the above example) (2). But sign language, notes Rochester University psychologist Aaron Newman offers “a unique opportunity to directly contrast these two means of marking grammatical roles within the same language” (2).
Newman employed functional Magnetic Resonance Imaging (fMRI) to zero in on the spatial-temporal brain activities that accompany both word order and inflection-based communication. What he uncovered was nothing short of remarkable. There exists a network of brain regions including the dorsolateral prefrontal cortex (DLPC), the superior and posterior temporal sulcus (STS), the caudate nucleus, the middle temporal gyrus (MTG), the angular gyrus (AG) and the left inferior frontal gyrus (IFG) that are operative during both the interpretation of word order and inflection processing (2). Importantly significant differences exist in the ‘relative weighting’ of activation in these regions depending upon which of these two modes of message transmission is being called upon (2). The DLPC and the right hemisphere AG are more dominantly active when word order-critical sentences are put in front of us. In contrast the MTG and the posterior STS are more active during inflection processing (2) The overarching conclusion borne out by the results of this study is that “specific parts of the neurocognitive system recruited for grammatical processing are dependent on the type of information that must be processed” (2).
Over the years my interest in language and brain function has been fueled by my own exposure to cultures outside of those of my native England. I grew up speaking Portuguese, Spanish and to a lesser extent French. Unlike English, these and other Romantic languages display a requirement for word inflection in both verb endings and noun genders. Whereas English leans towards compound verb usage, Portuguese, Spanish and French show complex verb endings (e.g., The English phrase I shall come translates into Portuguese as Eu virei). When I traveled last week to the Brazilian Society of Biochemistry meeting in Foz de Iguaçu in southern Brazil, I was relieved to find that I could slip almost effortlessly into both the written and spoken forms of Portuguese. It was a joy to find that, despite the odd non-conformity, my Portuguese had remained unadulterated over the years. Little did I know that I was employing cognitive functions that differed from those that I use in my more usual English setting.
On the flight out I settled down to read about the work of one Evelina Fedorenko who as an MIT psychologist has played an instrumental role in deciphering the functional hotspots of linguistic cognition (3). Her research has concentrated on mapping the ‘within language’ specificity (linguistic processing cognition) and ‘domain’ specificity (non-linguistic cognition) areas of the brain (3). Fedorenko and her close colleague Nancy Kanwisher have devised a ‘localizer task’ approach for studying brain function (3). By asking individual subjects to perform cognitive tasks that place demands on localized regions of the brain (eg: contrasting pronounceable non-words like florp with real words like flop), they have been able to identify those regions that “engage in retrieving the meanings of individual lexical items and in combining these lexical-level meanings into larger meaning structures” (3).
After getting back home from my trip, I had the chance to ask my father – a linguist by training – for his take on Newman’s and Fedorenko’s work. His principle observation was that sign language could only serve as a model for written words. Whereas sign language is sequential, spoken forms of language are multi-layered with sounds, grammar, vocabulary, intonation and gesture all acting together to achieve the conveyance of information. But what was plainly obvious to both of us was that through its sheer processing speed, the cerebral linguistic toolbox had no equivalent in anything that a carpenter might find on his workbench. Almost two decades ago brain biologist John Eccles noted that our linguistic capacity was pivotal in ensuring that we became the dominant species on our planet (4). The latest research is confirming Eccles’ assessment. And the brain architecture associated with language processing is turning out to be mind blowingly complex.
- Aaron Blank (2010) Sign Language Study Shows Multiple Brain Regions Wired for Language, http://www.rochester.edu/news/show.php?id=3610
- Newman AJ, Supalla T, Hauser P, Newport EL, & Bavelier D (2010). Dissociating neural subsystems for grammar by contrasting word order and inflection. Proceedings of the National Academy of Sciences of the United States of America, 107 (16), 7539-44 PMID: 20368422
- Evelina Fedorenko, Functional localization in fMRI studies of language, See http://web.mit.edu/evelina9/www/funcloc.html
- John Eccles (1991) Evolution Of the Brain, Creation Of The Self, Routledge Press, London, p.96