Language and the brain

    Many people assume the physical basis of language lies in the lips, the tongue, or the ear.  But deaf and mute people can also possess language fully.  People who have no capacity to use their vocal cords may still be able to comprehend language and use its written forms.  And human sign language, which is based on visible gesture rather than the creation of sound waves, is an infinitely creative system just like spoken forms of language.  But the basis of sign language is not in the hand, just as spoken language is not based in the lips or tongue.  There are many examples of aphasics who lose both the ability to write as well as to express themselves using sign-language, yet they never lose manual dexterity in other tasks, such as sipping with a straw or tying their shoes. 
    Language is brain stuff--not tongue, lip, ear, or hand stuff. The language organ is the mind. More specifically, the language faculty seems to be located in certain areas of the left hemispheric cortex in most healthy adults.  A special branch of linguistics, called neurolinguistics, studies the physical structure of the brain as it relates to language production and comprehension.  
Structure of the human brain. The human brain displays a number of physiological and structural characteristics that must be understood before beginning a discussion of the brain as language organ.  First, the cerebrum, consisting of a cortex (the outer layer) and a subcortex, is also divided into two hemispheres joined by a membrane called the corpus callosum.  There are a few points which must be made about the functioning of these two cerebral hemispheres.         
    1) In all humans, the right hemisphere controls the left side of the body; the left hemisphere controls the right side of the body. This arrangement--called contralateral neural control is not limited to humans but is also present in all vertibrates--fish, frogs, lizards, birds and mammals. On the other hand, in invertibrates such as worms, the right hemisphere controls the right side, the left hemisphere controls the left side. The contralateral arrangement of neural control thus might be due to an ancient evolutionary change which occurred in the earliest vertibrates over half a billion years ago. The earliest vertibrate must have undergone a 180° turn of the brain stem on the spinal chord so that the pathways from brain to body side became crossed. The probability that such a primordial twist did occur is also born out by the fact that invertibrates have their main nerve pathways on their bellies and their circulatory organs on their backs, while all vertibrates have their heart in front and their spinal chord in back--just as one would expect if the 180° twist of the brain stem vis-a-vis the body did take place.
    2.) Another crucial feature of brain physiology is that each hemisphere has somewhat unique functions (unlike other paired organs such as the lungs, kidneys, breasts or testicles which have identical functions). In other words, hemisphere function is asymmetrical. This is most strikingly the case in humans, where the right hemisphere--in addition to controlling the left side of the body--also controls spatial acuity, while the left hemisphere--in addition to controlling the right side of the body-- controls abstract reasoning and physical tasks which require a step-by-step progression. It is important to note that in adults, the left hemisphere also controls language; even in most left-handed patients, lateralization of language skills in the left hemisphere is completed by the age of puberty.
    Now, why should specialized human skills such as language and abstract reasoning have developed in the left hemisphere instead of the right? Why didn't these skills develop equally in both hemispheres. The answer seems to combine the principle of functional economy with increased specialization. In nature, specialization for particular tasks often leads to physical asymmetry of the body--witness the lobster's claws--where limbs or other of the body differentiate to perform a larger variety of tasks with greater sophistication (the same might be said to have happened in human society with the rise of different trades and the division of labor).
    Because of this specialization, one hemisphere--in most individuals for some reason it is the right hemisphere--came to control matters relating to 3D spatial acuity--the awareness of position in space in all directions simultaneously. Thus, in modern humans, artistic ability tends to be centered in various areas of the right hemisphere.
    The left hemisphere, on the other hand, came to control patterns that progress step-by-step in a single dimension, such as our sense of time progression, or the logical steps required in performing feats of manual dexterity such as the process of fashioning a stone axe. This connects with right-handedness. Most humans are born with a lopsided preference for performing skills of manual dexterity with the right hand--the hand controlled by the left hemisphere.  The left hand holds an object in space while the right hand mainpulates that object to perform tasks which require a step-by-step progression. Obviously, this is a better arrangement than if both hands were equally clumsy at performing complex, multi-step tasks, or if both sides of the brain were equally mediocre at thinking abstractly or at processing information about one's three-dimensional surroundings. So human hemispheric asymmetry seems to have developed to serve very practical purposes. 
    (By the way, left-handedness seems to be the result of inheritance of two copies of a gene which does not impart strong right-hand preference. The right-handed gene is dominant--in 25% of the population has no copy of this gene, presumably 12.5% percent of these non-handed individuals develop a righthandedness anyway, and 12.5% develop a tendency toward left handedness. At any rate, being left-handed doesn't seem to have any special effect on language acquistion or learning or on anything else innate to humans.)
    This general pattern of cognitive asymmetry was probably well established in our hominid ancestors before the language faculty developed. So why did humans evolve in such a way that the language faculty normally localized in the left hemisphere?  Why not in the right?  Clearly, the reason is that language, like fashioning a stone axe, is also a linear process: sounds and words are uttered one after another in a definite progression, not in multiple directions simultaneously. In the modern human, the feature of monolineal progression seems naturally to ally language with other left brain skills such as the ability to perform complex work tasks, or abstract step-by-step feats of logic, mathematics, or reasoning. Even among natural left-handers (in about 12.5 % of any human population, language skills are localized in the cortex of the left hemisphere in all but about 2.5% of the cases.  Some of these are individuals who received damage to the left hemisphere in childhood which, presumably, prevented language from localizing there; however, we don't know why language localizes in the right hemisphere of the brain in about one in fifty healthy adults. Like right or left handedness, it seems to correlate with nothing else in particular.
    How do we know that the left hemisphere controls language in most adults. There is a great deal of physical evidence for the left hemisphere as the language center in the majority of healthy adults.
    1) Tests have demonstrated increased neural activity in parts of the left hemisphere when subjects are using language.  (PET scans--Positron Emission Tomography, where patient injects mildly radioactive substance, which is absorbed more quickly by the more active areas of the brain). The same type of tests have demonstrated that artistic endeavor draws normally more heavily on the neurons of the right hemispheric cortex.
    2) In instances when the corpus callosum is severed by deliberate surgery to ease epileptic seizures, the subject cannot verbalize about object visible only in the left field of vision or held in the left hand.) Remember that in some individuals there seems to be language only in the right brain;  in a few individuals, there seems to be a separate language center in each hemisphere.)
    3.) Another clue has to do with the evidence from studies of brain damage. A person with a stroke in the right hemisphere loses control over parts of the left side of the body, sometimes also suffers a dimunition of artistic abilities. But language skills are not impaired even if the left side of the mouth is crippled, the brain can handle language as before. A person with a stroke in the left hemisphere loses control of the right side of the body; also, 70% of adult patients with damage to the left hemisphere will experience at least some language loss which is not due only to the lack of control of the muscles on the right side of the mouth--communication of any sort is disrupted in a variety of ways that are not connected with the voluntary muscles of the vocal apparatus. The cognitive loss of language is called aphasia, and we will discuss various types of aphasia in great detail tomorrow; only 1% of adults with damage to the right hemisphere experience any permanent language loss.
    Aphasics can blow out candles and suck on straws, even sing and whistle, but they cannot produce normal, creative speech in either written, spoken, or gestural form.  Sign language users also store their linguistic ability in the left hemisphere. If this hemisphere is damaged, they cannot sign properly, even though they may continue to be able to use their hands for such things as playing the drums, giving someone a massage, or other non-linguistic hand movements. Injury to the right hemisphere of deaf persons produces the opposite effect.
Experiments on healthy individuals with both hemispheres intact.
    4.) In 1949 it was discovered that if sodium amytal is injected into the left carotid artery, which services blood to the left hemisphere, language skills are temporarily disrupted.  If the entire left hemisphere is put to sleep, a person can think but cannot talk.
    5.) If an electrical charge is sent to certain areas of the left hemisphere (exactly which areas we will discuss tomorrow), the patient has difficulty talking or involuntarily utters a vowel-like cry  (although the production of specific speech sounds has never been induced by electrical charge). An electrical charges to the right hemisphere produces no such effect.
    6.) Musical notes and tones are best perceived through the left ear (which is connected to the spacial-acuity-controlling right hemisphere. In contrast, the right ear better perceives and processes the sounds of language, even linguistic tones (any form with meaning); the right ear takes sound directly to the left hemisphere language center.
    7.) When repeating after someone, most individuals have a harder time tapping with the fingers of the right hand than with the left hand. /Perform this experiment in class./
    8.) The language centers in the left hemisphere of humans actually make the left hemisphere bulge out slightly in comparison to the same areas of the right hemisphere. This is easily seen without the aid of the microscope. For this reason, some neurolinguists have called humans the lopsided ape.  Some paleontologists claim to have found evidence for this left-hemispheric bulging in Homo neanderthalus and Homo erectus skulls.
    Other primates also possess a left perisylvian area of the brain, but it doesn't seem to be involved in their communication.  Animal communication seems in fact to be controlled by the subcortical areas of the animal brain, much like human vocalizations other than language--laughter, sobbing, crying, as well as involuntary, word-like exclamations which do form part of language--are controlled in humans in the subcortex, a phylogenetically older portion of the brain that is involved with emotions and reflex responses.
    Tourette's syndrome, which produces random and involuntary emotive reflex responses, including vocalizations This type of disorder, which often affects language use, is caused by a disfunction in the subcortex. There is no filter which prevents the slightest stimulus from producing a vocal response, sometimes of an inappropriate manner using abusive language or expletives. These words are involuntary and often the affected individual is not even aware of uttering them (like "um" in many individuals) and only realizes it when video is played back. 
    This syndrome is not so much a language disorder per se as a disorder of the filters on the adult emotional reflex system--a kind of expletive hiccup. True language is housed in the cortex of the left hemisphere, not in the subcortical area that controls involuntary responses.
What can language disorders tell us about the brain's language areas?
    Certain types of brain damage can affect language production without actually eliminating language from the brain. A stroke that damages the muscles of the vocal apparatus may leave the abstract cognitive structure of language intact--as witnessed by the fact that right hemisphere stroke victims often understand language perfectly well and write it perfectly with their right hand--although their speech may be slurred due to lack of muscle control. We have also seen that certain disorders involving the subcortex--the seat of involuntary emotional response--may have linguistic side effects, such as in some cases of Tourette's syndrome.
    But what happens when the areas of the brain which control language are affected directly, and the individual's abstract command of language is affected? We will see that language disorders can shed a great deal of light on the enigma of the human language instinct.
SLI.  One rare language disorder seems to be inborn rather than the result of damage to a previously normal brain. I have said that children are born with a natural instinct to acquire language, the so-called LAD; however, a tiny minority of babies are born with an apparent defect in this LAD. 
    Certain families appear to have a hereditary language acquisition disorder, labeled specific language impairment, or SLI.  Children born with this disorder usually have normal intelligence, perhaps even high intelligence, but as children they are never able to acquire language naturally and effortlessly. They are born with their window of opportunity already closed to natural language acquisition. These children grow up without succeeding in acquiring any consistent grammatical patterns. Thus, they never command any language well--even their native language. As children and then as adults, their speech in their native language is a catalog of random grammatical errors, such as: It's a flying birds, they are. These boy eat two cookie. John is work in the factory. These errors are random, not the set patterns of an alternate dialect:  the next conversation the same SLI-afflicted individual might say This boys eats two cookies.  These sentences, in fact, were uttered by a British teenager who is at the top of his class in mathematics; he is highly intelligent, just grammar blind.    SLI sufferers are incapable of perfecting their skills through being taught, just as some people are incapable of being taught how to draw well or how to see certain colors. This is the best proof we have that the language instinct most children are born with is a skill quite distinct from general intelligence.
    Because SLI occurs in families and seems to have no environmental cause whatsoever, it is assumed to be caused by some hereditary factor--probably a mutant, recessive gene that interferes with or impairs the LAD. The precise gene which causes SLI has yet to be located.

SUMMARY

    Let's sum up three important facts about language and brain.
    First, humans are born with the innate capacity to acquire the extremely complex, creative system of communication that we call language. We are born with a language instinct, which Chomsky calls the LAD (language acquisition device).  This language aptitude is completely different from inborn reflex responses to stimuli as laughter, sneezing, or crying.  The language instinct seems to be a uniquely human genetic endowment:  nearly all children exposed to language naturally acquire language almost as if by magic.  Only in rare cases are children born without this magical ability to absorb abstract syntactic patterns from their environment.  These children are said to suffer from Specific Language Impairment, or SLI.  It is thought that SLI is caused by a mutant gene which disrupts the LAD. 
    The LAD itself, of course, is probably the result of the complex interaction of many genes--not just one--and the malfunction of some single key gene simply short-circuits the system. For example, a faulty carburetor wire may prevent an engine from running, but the engine is more than a single carburetor wire. Many thousands of genes contribute to the makeup of the human brain--more than to any other single aspect of the human body. To isolate the specific set of genes that act as the blueprint for the language organ is something no one has even begun to do.
    Second, the natural ability for acquiring language normally diminished rapidly somewhere around the age of puberty. There is a critical age for acquiring fluent native language. This phenomenon seems to be connected with the lateralization of language in the left hemisphere of most individuals--the hemisphere associated with monolinear cognition (such as abstract reasoning and step-by step physical tasks) and not the right hemisphere, which is associated with 3D spatial acuity, artistic and musical ability.  Unlike adults, children seem to be able to employ both hemispheres to acquire language. In other words, one might say that children acquire language three-dimensionally while adults must learn it two dimensionally.
    Third and finally, in most adults the language organ is the perisylvian area of the left hemispheric cortex. Yesterday we discussed the extensive catalog of evidence that shows language is usually housed in this specific area of the brain. Only the human species uses this area for communication.  The signals of animal systems of communication seem to be controlled by the subcortex, the area which in humans controls similar inborn response signals such as laughter, crying, fear, desire, etc.

Aphasia

    We know which specific areas of the left hemisphere are involved in the production and processing of particular aspects of language.  And we know this primarily from the study of patients who have had damage to certain parts of the left hemispheric cortex. Damage to this area produces a condition called aphasia, or speech impairment (also called dysphasia in Britain). The study of language loss in a once normal brain is called aphasiology.  
    Aphasia is caused by damage to the language centers of the left hemisphere in the region of the sylvian fissure. Nearly 98% of aphasia cases can be traced to damage in the perisylvian area of the left hemisphere of the cerebral cortex. Remember, however, that in the occasional individual language is localized elsewhere; and in children language is not yet fully localized.
    Strokes cause 85% of all aphasia cases; other causes include cerebral tumors and lesions. One in 200 people experiences aphasia, with males more at risk. Gradual recovery is possible in 40% of adult cases; pre-pubescent children are much more likely to recover from aphasia, with the language faculty localizing in another, unaffected area of the brain, usually the perisylvian cortex of the right hemisphere.  Generally, the more extensive the injury, the greater the likelihood of permanent damage.
    But we have seen that language is a complex of interacting components--consonants and vowels, nouns and verbs, content words and function words, syntax and semantics.  Could it be that these components are housed in particular sub-areas of the left hemisperic perisylvian cortex?  We haven't pinpointed whether nouns are stored separately from verbs, or where the fricative sounds are stored.  There is no conclusive proof for that type of specialization of brain tissue.  But there is compelling evidence to believe that two special aspects of language structure are processed by different sub-areas of the language center.  We know this because damage to specific areas of the peresylvian area produces two basic types of aphasia.
    Each of these two types of language loss is associated with damage to a particular sub-region of the perisylvian area of the left hemispheric cortex. 
    (1861) Paul Broca discovered Broca's area (located in the frontal portion of the left perisylvian area) which seems to be involved in grammatical processing. (While parsing sentences such as fat people eat accumulates, there is a measurable burst of neural activity in Broca's area when the last word is spoken.) Broca's area seems to process the grammatical structure rather than select the specific units of meaning.  It seems to be involved in the function aspect rather than the content areas of language)
    Broca's aphasia involves difficulty in speaking.  For this reason it is also known as emissive aphasia. Broca's aphasics can comprehend but have great difficulty replying in any grammatically coherent way.  They tend to utter only isolated content words on their own. Grammatical and syntactic connectedness is lost.  Speech is a labored, irregular series of content words with no grammatical morphemes or sentence structure. (Read example) Grammar rules as well as function morphemes are lost. Broca's aphasia is also known as agrammatic aphasia. Grammar is destroyed; the lexicon more or less preserved intact.
    (1875) Karl Wernicke:  Wernicke's area (in the lower posterior part of the perisylvian region) controls comprehension, as well as the selection of content words.  When this area is specifically damaged, a very different type of aphasia usually results, one in which the grammar and function words are preserved, but the content is mostly destroyed. 
    Since Wernicke's aphasia involves difficulty in comprehension, in extracting meaning from a context, it is also known as receptive aphasia. Wernicke's aphasics easily initiate long-winded, fluent nonsense, but don't seem able to respond specifically to their interlocutor (unlike Broca's aphasics, who can understand but the have difficulty replying). Wernicke's aphasics often talk incessantly and tend to utter whole volumes of grammatically correct nonsense with relatively few content words or with jibberish words like "thingamajig"  or "whatchamacallit" instead of true content words. (Read example.)  Because Wernicke's aphasia patients can utter whole monologs of such contentless grammatical babble, hardly letting their interlocutor get a word in edgewise, their affliction is also known as jargon aphasia.
    The normal human mind uses both areas in unison when speaking. Apparently, normal adults use the neurons of Wernicke's area to select sounds or listemes.  We use the neurons of Broca's area to combine these units according to the abstract rules of phonology and syntax--the elements in language which have function but no specific meaning-- to produce utterances.
Review:
Broca's aphasia--emissive aphasia--agrammatic aphasia: difficulty in encoding, in building up a context, difficulty in using the grammatical matrix of phrase structure, difficulty in using the elements and patterns of language without concrete meaning.  Broca's area apparently houses the elements of language that have function but no specific meaning--the syntactic rules and phonological patterns, as well as the function words--that is, the grammatical glue which holds the context together.
Wernicke's aphasia--receptive aphasia--jargon aphasia: difficulty in decoding, in breaking down a context into smaller units, as well as in selecting and using the elements of language with concrete meaning.  Wernicke's area apparently houses the elements of language that have specific meaning--the content words, the lexemes--that is,  the storehouse of prefabricated, meaningful elements which a speaker selects when filling in a context.
    Let's review what these two areas--Broca's and Wernicke's seem to be telling us about the way language is stored in the brain.  Language obviously consists of these two aspects working together in unison:
    1) a very large but finite number of elements with specific form and meaning (morphemes, words, phrases--the lexicon, or set of listemes, on the other hand--). These ready-made elements seems to be stored in Wernicke's area.
    2) a fairly small number of patterns with virtually no limit on the specific meaning they can express (the phonology and syntax--the grammar of language, the abstract blueprint by which the prefabricated units of Wernicke's area are combined). These abstract patterns seem to be stored in Broca's area.
    Roman Jakobson, a Russian born linguist who made extensive studies of aphasia in the 1950's, noted that both types of the aphasic lose language in the exact reverse order that language is acquired by a child-- -s of plays, the genitive 's, then finally plural s.  This is true of the sound pattern, as well.  In instances of gradual, progressive degeneration of the language centers of the left hemisphere, the aphasic's loss of phonology is the mirror image of the acquisition of elements in childhood.
    These two areas have been implicated even more broadly with the human abilities to deal with signs. Roman Jakobson also noted that normal language function involves an interaction of two different associative properties of meaning: association by contiguity and association by similarity. (Perform a word test with the word knife.) Jakobson conducted aphasia studies in the 50's and 60's which revealed that each of the two basic types of linguistic aphasia--Broca's emissive, or agrammatic, aphasia and Wernicke's receptive, or jargon, aphasia-- also affects a specific one of these two aspects of linguistic association in a predictible way. 
    Broca's aphasia (emissive, agrammatic) also involves contiguity disorder. We have seen how Broca's aphasics have difficulty in building up a context. Jakobson showed that Broca's aphasics also lose their general ability to communicate in terms of spatial and temporal contiguity:
    1.) The Broca's aphasic can name synonyms and antonyms but not contiguous concepts:  champagne, wine, but not cork, tipsy, hangover.  knife-->dagger, sword, but not fork, spoon, table, to eat with.
    2.) Broca's aphasics also evince an inability to comprehend metonymy, synecdoche, tropes based on contiguity.
    3.) All understanding of word building, connecting morphemes to build words, is lost.  The Broca's aphasic can say jewel but cannot build such derivates as jeweler, jewelry; or he can sayemploy but not employer, employee.. He shows an inability to combine or break down linguistic units.  Compound words such as Thanksgiving are perceived as indivisible wholes.  Broca's aphasics cannot pronounce new or unfamiliar words: big, give, but not gib. Cannot form the plural of wug or any other plural. If the word exists only as a ready-made unit, it cannot be built up out of smaller units. Linguistic expression is limited to selection of ready-made units; all contiguity-based relations are impaired--content is retained but context is lost.
    Wernicke's aphasia (receptive, jargon aphasia), on the other hand, involves similarity disorder. We have seen that for Wernicke aphasics, conversation is easily initiated but lacks content. Connective words such as conjunctions, pronouns, prepositions remain, but selection of content words is impaired; content words tend to be absent or replaced by general terms such as thing, stuff, whatchamacalit.
    Wernicke's aphasics also lose their ability to perform language skills based on association by similarity. They cannot form or comprehend metaphors and similes and compensate by using associations based on contiguity.
    1.) Wernicke's aphasics cannot produce synonyms or antonyms: Instead, the patient will name things contextually associated with an object. When asked to define the word knife, a Wernicke's aphasic might say to eat with or knife, or even knife and fork; he would not say dagger, sword, or anything similar.  When asked to repeat the word glass he might say window, or something contiguous with glass.
    2.) Wernicke's aphasics evince an inability to use or comprehend metaphor, simile--tropes based on association by similarity.
    3) Linguistic expression is limited to contiguity-based relations--context is retained while content is lost; all skills based on the recognitions of similarity or dissimilarity are impaired and replaced by expressions of contiguity.
    Jakobson was the first to note that Broca's and Wernicke's area seem to control these different and complementary associative properties of meaning.  In the conversation of a normal individual, both regions of the brain work in unison (healthy people even have a hard time separating out what associations are based on similarity and which are based on contiguity).  But in aphasic patients, either context and contiguity (Broca's) or the content and similarity (Wernicke's) tend to be impaired (though each individual aphasic has a different combination of these impairments). If Broca's and Wernicke's regions are both severely damaged--in other words, if the entire linguistically relevant perisylvian area of the brain is damaged--the patient loses all language ability; he experiences aphasia universalis, or the total loss of language.
    Recent studies have shown that Broca's and Wernicke's areas are actually contiguous portions of the brain--part of a single area-- rather than separate areas (the connection is hidden by the convolutions of the brain). Some recent neurolinguists have called the band of linguistically relevant neural tissue which contains Broca's and Wernicke's areas the perisylvian area.
    This perisylvian area, apparently, is the language organ in humans. Other animals lack this area, although monkeys and other primates show a small development of the area of their brain that is analogous to Broca's area, this area does not seem to play a role in their communicative skills. In humans, the perisylvian area seems to be the seat of the language skills in most adults. It is here that language skills are normally localized as the brain matures.
    It is not possible to say precisely that Broca's and Wernicke's areas have the same language functions in all adults; sometimes language skills seem to be localized in slightly different areas of the adult brain. Broca's area does not always control grammar in the same way that the liver always produces bile and the pancreas always produces pancreatic juice. Unlike the liver, pancreas, and other organs, the developing brain seems to have a property called plasticity, which allows functions to be localized in a variety of possible places as the brain matures. This is why damage to Broca's area does not always cause the typical agrammatic aphasia; and damage to Wernicke's area does not always cause the typical jargon and babbling symptoms of Wernicke's aphasia.
    There is also some evidence that sub-areas of Broca's area or sub-areas of Wernicke's area may store aspects of language as specific as the comprehension of nouns and verbs or the ability to break a sentence down into words, on the one hand, and the word into individual morphemes or phonemes, on the other. And yet in every individual the ability to communicate seems to involve an interaction of one part of the cortex which controls selection and another part which controls the combination of selected units. These areas, in turn, are connected by a dense set of neurons and so are really extensions of one another. The complex interaction of these neurons gives us our complete language faculty.
The semiotic organization of the brain
    Jakobson's aphasia studies has implications for the study of the structure of human sign systems in general (semiotics).  Language is only one of the human manifestations of semiotic (sign-sensitive) behavior.  The dual aspects of similarity/selection and contiguity/combination, seen so clearly in the functioning and imparement of language, actually appear as primal forces in all forms of human expression, not just language.
    
    James Frazer (The Golden Bough)-- describes two types of magic rites:  charms based on similarity-- sympathetic or imitative magic  vs. contagious magic.
    Different genres of literature rely to varying degrees on the two types of associations. Most poetry relies more on similarity and less on connected context; most types of prose, on the other hand, relies more heavily on contiguity, on a connected context.
    Similarity and contiguity often alternate as dominant forces of expression in art and literature.  romanticism vs. realism; impressionism. vs. cubism.
In other words, all of our meaning-based systems, not only language, seem to involve a constant interplay of Wernicke-based similarity relations, on the one hand, and Broca-based contiguity relations, on the other.
Conclusion. And so, our course began with a discussion of language and mind and it ends with a discussion of language and the brain. It would seem that the perisylvian area of the left hemisphere is indeed not only the primary organ of language; it also seems to underlie a broader range of cognitive powers that make humans unique. Speech may consist of sound vibrations or visual symbols superficially not unlike the signs of animal communication, but language--the abstract system that underlies the production of speech--is a property of the uniquely human aspect of the mind. Language is brain stuff.  And it seems that the human brain--among that of all other species--is uniquely constructed to manipulate complex sign systems such as language, art, and other representational behavior.  We are born with the capacity to acquire language in childhood because of the genetically planned structure of our brains. This property of the brain has been called the language instinct. Bees seek nectar, birds build nests, spiders spin webs. We humans create language.
    This language instinct is undoubtedly why we humans have become--along with such enormously successful creatures as earthworms and algae--one of the most influential species ever to inhabit the earth.

    There is much left to discover in the field of linguistics and especially neurolinguistics, so keep your ears--that is, your perisylvian area--attuned for new revelations.