Language and the Brain

Text-only Preview

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
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
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
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.
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
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.
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.
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
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,

Document Outline

    • Linguistics 201: Language and the Brain