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Límulus

From the brain to language

Text by Fernanda Pérez-Gay Juárez

“Words! Mere words! How terrible they are!

How clear, and vivid, and cruel! One could not escape from them!

And yet what subtle magic there was in them! They seemed to be able to give a plastic form to formless things, and to have a music of their own as sweet as that of viol or of lute. Mere words!

Was there anything so real as words?”

-O. Wilde, The Picture of Dorian Gray.

 

From the brain to language and back

Let us begin by talking about the brain. An organ that weighs about 1.5 kg and is made up of different types of cells, through which, one is able to transmit electric impulses to its neighbor: the neuron. The neuron has been drawn in the shape of a star with a lightning bolt –called axon– that comes out of its peaks –called dendrites. A neuron is able to generate potentially electrical changes and transmit them through its axon, a sort of cable that will connect to other neurons. The length of axons –these cell extensions– allows the nervous impulses to go through long distances.

When we talk about “connections,” we really mean synapsis.

A synapsis is the contact space between neurons, where the nerve impulse of neuron 1 will liberate extremely small molecules called neurotransmitters that will produce changes in neuron 2.

Let’s try to imagine these astronomical digits: Our brain contains 100 billion neurons, and each one can connect to around 10,000 more neurons. These connections between neurons create circuits. A neural circuit is a series of neurons that, through constant communication, will produce activity at the same time it goes about its function.

Let us now shift to the territory of language: A system of symbols that has served humans as a means to communicate with the world that surrounds them. Each language is a shared code that shapes our identity and, in normal circumstances, it takes up our conscious thought almost entirely. Language is the prosthesis that allows us to express the information we process, bridging the gap between our mind and what is outside. In addition, it’s one of humans’ exclusive ability, which contrasts with the fact that they have the same brain cells and synapse mechanisms as other animals.

The philosopher Wittgenstein stated that “the limits of language are the limits of thought.” Not all thought, however, is made of language. Feelings, imagination, and the spatial representations of the world that surrounds us are examples of thought that is not made up of words. There are also pre-verbal concepts and impressions that reach our conscious thought. On the other hand, the language of our verbal thought is not necessarily the same as our spoken language.  Jerry Fodor referred to this continuous mental monologue as language of thought, using the ingenuous term “mental” to refer to inner or non-communicative language.

Nowadays almost all thinkers of different disciplines accept that the mind is a function of the brain. But within this affirmation, questions emerge that are not easy to answer. When we try to address language from the point of view of neuroscience, we face quite a few: how is it that thousands of nervous cells that make up our brain cortex conceive the electric activity that originates language? What connections are needed, what circuits have to be formed to develop this intrinsic human property? What do we know about what happens in our brain when we talk, when we write, when we listen or read? What areas or systems of our brain participate in the processing of language?

Let’s go back to the anatomy of the brain. The brain is divided in two hemispheres, each one contains five lobes: the frontal, parietal, occipital, temporal, and in the depths of the union between the frontal and temporal lobe, the insular lobe. In the cerebral cortex, these lobes, millions of bodies of neurons, organized in six layers, are folded to originate the turns and creases where the majority of the cognitive functions take place.

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Drawing by Alex Konahin (http://konahin.com/)

Broca, wernicke, aphasias and the first neural language model

The first to find evidence that related language with a specific area of the cerebral cortex was Pierre Paul Broca, a French anthropologist and neurologist that in 1861 tended for a patient that suffered from epilepsy and aphasia, which means, he had lost the ability to emit coherent language. He understood when spoken to; he could say isolated words, whistle and even sing. His vocal cords and articulatory phonetics were intact. However, this patient could not grammatically structure sentences or express written ideas. When the patient died, his brain was donated to the Society of Anthropology and, in the postmortem examination, Paul Broca found damage in the back of the left frontal lobe. After studying eight new cases of patients with similar clinical problems, he found, in the post-mortem exams, that they all had damage in that area of the brain, always on the left side. After these discoveries in 1864, he announced: “Nous parlons avec l’hemisphère gauche!” (We speak with the left hemisphere!).

This was only the beginning. Paul Broca’s discovery of a first cerebral language settlement left many questions unanswered. Twelve years later, it was Karl Wernicke, at 26 years of age that made the following contribution. Wernicke found patients in his clinical work with a different type of aphasia. Although they articulated complete words, the subjects studied by Wernicke did not understand when spoken to or emitted sentences without a logical sense. After studying their brains postmortem, Wernicke found that the damaged area in these cases was different: it was located in the frontal part of the temporal lobe, the area where the latter unites with the parietal and occipital lobes.

Based on these discoveries, Wernicke proposed the existence of a second area of language –specialized in understanding and not in the production like Broca’s area– which was also in the left hemisphere. This knowledge worked as a base to create the first neural model of language, which involved two separate systems that acted in a parallel matter: a sensory system of language –to perceive and understand it– located in the area previously described of the temporal lobe, and a motor system of language –to create and emit it– that would be located in Broca’s area. Wernicke proposed that both areas were connected by the so-called arcuate fasciculus, a group of axons that go from one area of neurons to another.

Currently, we know that Wernicke’s area of the brain is conveniently surrounded by areas destined to hearing and Broca’s area is surrounded by areas of the brain that control the movement of the muscles that make phonation possible. But we would find that out later. Without knowing the details, Wernicke’s model already provided a very good explanation for how we went from seeing to hearing a word, to associating it with meaning as well as emitting new words or sentences through oral and written communication.

In 1960, Norman Geschwind used recently acquired knowledge on other areas of the brain –missing in Wernicke’s time and outlined the following model, known as Wernicke– Geschwind which, largely, prevails until today:

The first steps to process language occur in areas of the brain destined to hearing –when we hear someone talk–, or vision –when we read–. We know today that these areas are found in the temporal and occipital lobe respectively. Here is where we identify that which we see or hear as a word, and a first mental image is created. This mental image will then go to an area of the brain known as angular gyrus, which is found near the union of the parietal, temporal and occipital lobes. This area transforms the visual and hearing stimuli into a neural code that will then go to the Wernicke area to be decoded. Thus, the content of language is recognized by the brain and related to its meaning, which is stored in the memory of the subject in question. The same way, information will be directed to Broca’s area too, where the neurons contain not only a series of grammatical rules but also patterns to create a motor representation, that is, of the necessary movements to create the words with which to respond to the original stimulus.

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Drawing by Mateo Pizarro

Language and news

The Wernicke-Geshwind model has such amazing strength that based on it, neuroscience has continued researching this human phenomenon through decades. However, with the coming of neuroimaging techniques that allow us to observe counterparts of cerebral activity as a subject executes a task, we’ve created a more complex vision of things.

To this day, we know that the linguistic abilities of humans are not exclusively found in one or two cerebral areas. In reality, there are multiple cerebral systems, relatively segregated, which cooperate in the processing and emission of language. These systems are located primarily in the frontal and temporal lobes.

One of the most prominent facts was the discovery that language is not an exclusive function of the left hemisphere. It is clear that language processing depends to a large extent on the function of the left hemisphere. Regardless of being left handed or right handed, we know today that more than 95% of human beings use the left hemisphere for grammar, vocabulary, phonetic assembly and the creation of language. But it doesn’t end there. Certain studies have shown that the areas in the left hemisphere that are destined to processing the content and meaning of language, in the right hemisphere are in charge of processing everything that goes along with language and is not coded in words, for example, prosody, which is the tone of voice given to language, changing its intention. The emotional changes in the tone of voice create changes in activity in the right hemisphere, in the frontal lobe as well as temporal.

Recent research has also elaborated Wernicke’s area as part of a vast system that associates sounds with concepts. Which is why, even if we kept hearing intact, patients with damage to this area of the brain are unable to understand what they are told. The cerebral system that associates meaning in the so-called “semantic process” of language is intricate, it implies diverse areas and is related to the memory circuits of each individual, which is what we have learned through our experience.

We must not be fooled by the complexity implied in the studies that have originated in what we know today of how our brain processes and generates language, we must accept that we are still far from knowing how a series of cells that carry electricity conceive a symbolic system of meanings, which allows us to expand further than our own mind. And, although neuroscience is a difficult discipline, sometimes, just by looking at the lines that create brain waves on a screen or the numbers that result from calculations that try to measure the areas of the cerebral cortex that are more active in certain conditions, we might think that all this is sterile compared to the beauty of two words that fit beautifully and cause a reaction in us. But, considering that it all came from the activity of that mass of cells we have in our brain, is it not fascinating to go deeper in the how and why?

 

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