looking for language in the brain

Looking for language in

the brain

Babel The Language Magazine | August 201712

Feature Looking for language in the brain

Patrick C. Trettenbrein offers a round-up of research into language and the brain, from the early days to contemporary studies that use a variety of neuroimaging techniques, and sketches the current relationship between linguistics and neuroscience.

The realisation that ‘minds are what brains do’ is frequently considered to constitute the

defining insight of our times. After all, isn’t it the case that the technological advances of the past decades have made it possible for us to study brain activity ‘online’ in a non-invasive manner, thereby paving the way for our contemporary understanding of the brain as the home of the mind? While this certainly makes for a nice story, it couldn’t be further from the truth: the archaeological record reveals that ancient Egyptians already knew about the mind-brain connection. They opened up skulls, presumably either to relieve pressure on the brain after injury or release evil spirits. And there is even older evidence of trepanation dating back to prehistoric times (yes, all of this was pre-anaesthesia).

The insight that the mind may be related to what the brain

does is therefore a rather old one that has seen a renaissance in the past century or so. But what about the connection between the brain and language? The whole enterprise of what we now call neurolinguistics, or the cognitive neuroscience of language, started in the nineteenth century, when the young French physician Pierre Paul Broca attended to a patient with a peculiar illness. A 30 year-old man named Louis Victor Leborgne had been admitted to a mental hospital in a Parisian suburb having suddenly lost the ability to speak; all he could utter was the syllable ‘tan’ (which would become his nickname). While his family had first thought his condition to be only temporary, Tan had been in the mental hospital more than ten years by the time Broca attended to him; his physical condition had worsened considerably and he had developed gangrene.

Broca was interested in language and immediately intrigued by Tan. Although his

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right arm was paralysed, Tan was still able to communicate using his left hand, and Broca soon noticed that his lack of productive language didn’t equate to a lack of other mental capacities. Tan died a few days after he had been admitted to surgery, aged 51. A biopsy of his brain revealed an extensive lesion in the left frontal area. In a paper published in the bulletin of the Société Anatomique, Broca hypothesised that this region must be critically involved with what he called articulate language. Nowadays, Tan’s condition and the affected brain region are known as ‘Broca’s aphasia’ and ‘Broca’s area’ respectively.

It seemed that the phrenologists had been right all along. The central idea of phrenology was that particular aspects of the ‘soul’, and especially personality traits, were linked to different parts of the brain and its size. So far so good, but phrenologists went one step further by claiming that they could even ‘diagnose’ someone’s personality by inspecting the bumps of their skull and then drawing conclusions about the extent to which a particular trait was ‘developed’ in the person examined.

Needless to say, phrenology was hopelessly unscientific, and was soon overturned and abandoned. However, phrenologists’ fundamental idea remains sound: it is true that specific (cognitive) functions can be attributed to particular parts of the brain, especially the cortex. The brain consists of designated areas that, by and large, seem to be specialised for doing particular things. This is usually termed ‘localisation of function’. For example, there is a visual cortex at the back of the brain that takes

care of visual input. Similarly, there are sensory and motor cortices in both hemispheres that are crucial for voluntary movement of the contralateral half of the body. The Canadian neurosurgeon Wilder Penfield and his colleague Herbert Japser first mapped these sensory and motor cortices in incredible detail using data obtained by electrically stimulating the brain during surgery on epileptic patients who were awake. In 1951, they published a book that described the cortical homunculus, the odd-looking figurine illustrating the amount of cortex devoted to a given body part with disproportionally large hands, lips and face that many will remember from their biology textbooks. In retrospect, Broca’s case study of Tan therefore constitutes the first attempt at linking a particular part of the cortex, more precisely the inferior frontal cortex, to a specific lack of (cognitive) function.

Against this background, it should be considered an amusing turn of history that only at the beginning of this century did cognitive neuroscientists unravel

the preserved brain of Tan in a Paris museum, putting it into a magnetic resonance imaging (MRI) machine to perform a structural scan and finding that Broca’s famous patient actually hadn’t suffered from a lesion typical for Broca’s aphasia. In addition to the extensive lesion in Tan’s brain in the area to which we now refer to as Broca’s area, the brain also exhibited an extensive subcortical lesion that destroyed many of the white matter pathways linking up different parts. Broca had no way of noticing this without destroying the specimen, which he chose not to do. But from our contemporary perspective this finding serves as a reminder that establishing the brain-language relationship is not a straightforward task.

Fast forward to the twenty-first century. For a long time it was mostly neurologists and, later, neuropsychologists who were interested in the neural underpinnings of language. Of course, it was clear to linguists that language, being a mental capacity, would ultimately somehow be implemented neurally, yet many thought the

Cortical means part of the cortex, the outer layer of the brain, whereas subcortical refers to structures underneath cortex. Cortex is the most recent addition to the vertebrate brain; subcortical structures and other parts of the brain are evolutionarily older.

Contralateral refers to the side of the body opposite to that on which a particular structure occurs. With regard to the brain, hemispheric control is always contralateral so that the left hemisphere controls the right side of the body and vice versa.

(f)MRI is short for (functional) magnetic resonance imaging, a neuroimaging technique that uses a magnetic field and pulses of radio wave energy to take pictures of the brain or body. In functional imaging studies, changes in the blood flow in the brain are being measured while the subject in the scanner is performing a behavioural task.



idea of studying language in the brain to be only a very distant goal. The so-called ‘cognitive revolution’ in linguistics in the 1950s had little immediate effect on this overall situation: progress in the theory of computation enabled linguists to characterise languages and language capacity using formal grammars. While this allowed for generalisations that hold across languages to be discovered on the computational level, no one had any idea how such an abstract and formal characterisation of a grammar would actually be implemented in the brain. Eric Lenneberg was the first to produce a detailed study of the biological basis of the human language capacity in the 1960s, and he concluded that there could be little doubt that language capacity was a feature of human biology. However, he had little to say about the connection between the linguistic theory of his day and brain science and biology. Strikingly, this is by and large still true today; while there has been significant progress in identifying parts of the brain that are crucially involved in language processing, it is far

from clear how linguists’ abstract description of a grammar will ultimately turn out to be related to what is really going on in a brain during language processing.

The classical model of language in the brain, still found in many textbooks today, is the Wernicke-Geschwind model. This model distinguishes between the understanding of language and the production of language: Broca’s area in the frontal cortex is deemed

responsible for assembling morphemes and language production, whereas Wernicke’s area in the temporal cortex houses the semantic component and, in cooperation with the adjacent auditory cortex, is considered responsible for understanding spoken language. The two areas are connected via a white matter pathway called the arcuate fasciculus, which enables the two areas to exchange information. While this somewhat simplistic model is not fundamentally wrong, the contemporary picture of language in the brain looks quite different. The advent of a variety of neuroimaging techniques has revealed that the networks of the brain that are involved in language-processing are more widespread than traditional models assumed. Further, much recent research questions the focus on the cerebral cortex (which is, after all, only the ‘outer layer’ of the vertebrate brain), as many evolutionarily older sub-cortical structures such as the basal ganglia, thalamus, and hippocampus have been found to also play a role in language processing.

Among the most interesting experiments in neurolinguistics, at least from the point of view of linguistics, are those that have taken an observation made by theoretical linguists and tried to subject it to empirical testing using a variety of neuroimaging techniques. One such experiment was performed in the 2000s by a group centred around the linguist Andrea Moro, in Milan. Linguists around the world had previously shown on theoretical grounds that the degree to which different languages might vary is not unbounded, as was previously thought. Instead, there are clear limits on what is and

Schematic illustration of the organisation of human cortex, singling out the canonical language regions in the Wernicke-Geschwind model of language processing: Broca’s and Wernicke’s area in the left hemisphere

White matter refers to areas in the brain consisting of so-called myelinated axons that provide a means for passing on signals between nerve cells.

Grey matter refers to parts of the brain that consist mostly of neurons’ cell bodies, synapses, and other cells. The difference in colour arises from the presence or absence of myelin, which serves as a kind of ‘insulation’ for nerve fibres.

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what is not a possible (human) language. Take, for example, the fact that rules in natural languages are always structure-dependent – linguistic rules do not seem to care about the linear arrangement of the sentence’s constituent parts. No human language negates a sentence by always putting the negation word as the third element in the string of words that constitute a sentence: there are examples where things may at first seem to work like that, but the simpler linear rules are actually never used. But wouldn’t it make things a whole lot easier if languages actually worked that way? Humans automatically infer and use structural information in language, and this is one of the reasons why programming a computer to process natural language is but a straightforward task. Strikingly, Moro and colleagues showed that our brains care deeply about the nature of the rules that we apply in language.

In a set of experiments using fMRI the Milan researchers around Moro had their subjects learn bits of Italian and Japanese, languages of which they had no prior knowledge. In one condition, subjects had to learn rules that were actually part of that language, whereas the second condition required them to learn a language that used either Italian or Japanese words, yet employed impossible rules. Researchers were able to show that the participants’ brains seemed to treat the stimuli in each condition in different ways. Interestingly, only learning rules of real Italian or Japanese over time led to an increase in neural activity in a canonical language region: Broca’s area. Of course, subjects could learn ‘unreal’ Italian or Japanese rules just as well: after all, humans

are quite smart. But the fMRI data suggests that participants subconsciously treated the unreal rules as if they were solving a puzzle: they could figure it out easily, yet the automaticity and specificity associated with linguistic processing only occurred when the rules they were learning did not violate universal linguistic principles. Behavioural work in the 1990s with Christopher, a savant who had an outstanding capacity for language learning, contained a prediction of these results: Neil Smith and Ianthi-Maria Tsimpli found that Christopher could readily acquire any nonsense language with which researchers confronted him, yet he was unable to learn the language if it relied on impossible rules.

More recently, another group of researchers based in Paris and led by Stanislas Dehaene has shown that human brains are sensitive to the size of constituent structures. They found that inferior frontal

(roughly Broca’s area) and posterior temporal regions of cortex exhibit a parametric increase in activation in response to stimuli that always comprise 12 words or pseudo words, yet an increasing number of constituents. This suggests that the brain’s language network comprises regions that are specialised for processing abstract syntactic information independent from other aspects of language. In a similar spirit, recent work at the Max Planck Institute for Human Brain and Cognitive Sciences in Leipzig, Germany has shown that the preference of Broca’s area for processing syntactic information can be studied in even greater detail, as specific parts of Broca’s area have been found to be highly sensitive to the presence or absence of syntactic structure even when using very simple sets of stimuli, for example, when contrasting two-word phrases such as ‘read magazines’ and two-item lists such as ‘table, magazines’.

Press releases issued by university press offices frequently feature colourful pictures of brains, alongside claims that ‘researchers have identified the neural correlates of X’. But what does this really mean? Most of what is currently understood about the brain is actually limited to two radically opposed levels: the micro level of neurons, synapses, and molecules, and the macro level of functional modules, brain regions, and networks. The still-standing challenge for neuroscience today is to solve the question of how to link up the micro and the macro levels; that is, to find out what is going on ‘in between’. Contemporary means for neuroimaging used in studies with human subjects are no exception: the

“Humans automatically infer and use structural information in language, and this is one of the reasons why programming a computer to process natural language is but a straightforward task. Strikingly, Moro and colleagues showed that our brains care deeply about the nature of the rules that we apply in language.”



electroencephalogram (EEG) offers excellent temporal resolution but poor spatial resolution of entire brain regions, whereas functional magnetic resonance imaging (fMRI) enables us to track changes in blood flow with a high spatial resolution but very poor temporal resolution. It is also important to keep in mind that fMRI studies are quite indirect: they do not measure neural activity as such, instead picking up on metabolic changes from which neural activity is inferred. Pictures of the brain with colourful blobs and strands only provide a very impoverished and static view of what is really going on.

The contemporary picture

of language processing in the brain relies on an understanding of language as what researchers call a network of networks: different parts of the brain might be more or less specialised for doing a particular thing, but all of higher cognition – including language – has been found to rely on extensive corticocortical and cortical-subcortical networks, that is the interplay of brain regions in different parts of cortex, subcortical structures, as well as the different fibre pathways connecting them. Therefore, Broca’s and Wernicke’s areas still play a crucial role, but are nowadays considered to be embedded in much more extensive networks. The functions usually attributed to them have also changed. For

example, it has been shown that there is no clear-cut anatomical distinction between language production and comprehension, as the Wernicke-Geschwind model would have it.

The direct consequence of this development is that the idea of localisation of function has been called into doubt. Of course, hardly anyone doubts that Penfield’s work on motor and sensory cortices is valid. But determining what is an appropriate characterisation of the function of a particular part of the brain often turns out to be quite complicated, especially when it comes to higher cognition and language. For example, what we nowadays refer to as Broca’s area has been shown to be involved in a variety of cognitive processes, not only language processing. Researchers have thus sought to characterise the role of so-called language areas in functional terms by trying to link them to computational theories of cognitive functions. For example, Broca’s area has been shown to be involved in motor planning, musical cognition, and language, leading some researchers to claim that Broca’s area is actually responsible for processing sequences and hierarchical structure in general, as these play a role in each of these three domains of cognition. While certainly not a perfect match, this makes for a possible first point of contact between neuroscience and linguists’ abstract description of formal grammars.

The current state of our interdisciplinary search for language in the brain, then, is best characterised by the wording of a Facebook relationship status that aptly captures the relationship of linguistics and neuroscience: “It’s

complicated”. Unlike the visual, auditory, motor, or sensory cortices, there is no analogous ‘language cortex’. The human brain is clearly specialised for language, yet language is kind of all over the place and requires the cooperation of many regions of the brain, which is why it seems somewhat unlikely that we will ever be able to pin down exactly one brain region, fibre tract, or similar that is truly unique to humans and exclusively involved in language processing. Instead, the current most promising guess is that our brains are equipped with a unique combination of ancient pre-linguistic neural systems that, only in this particular combination, give rise to our linguistic abilities and mode of cognition. But there never was any reason to assume that figuring out how brains ‘do language’ was going to be easy. After all, cognitive (neuro-)science in itself is a somewhat absurd endeavour – the mind/brain is trying to understand itself! ¶

Find out more

Patrick C. Trettenbrein studied cognitive sciences with a focus on linguistics and philosophy in Graz and London. He is a PhD candidate in neurolinguistics at the University of Graz in Austria, and a visiting researcher at the Max Planck Institute for Human Brain & Cognitive Sciences in Leipzig, Germany.

BooksDavid Kemmerer (2015) Cognitive Neuroscience of Language, Psychology Press.Andrea Moro (2015)The Boundaries of Babel: The Brain and the Enigma of Impossible Languages (2nd edition), MIT Press.

MediaA Ling Space guide to language and the brain – youtu.be/Yq7ozVixqDs

Neurons and synapses are nerve cells that constitute the basic building blocks of the brain and the structures that permit neurons to pass on signals.

Babel The Language Magazine | August 2017 17


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