Biological Basis of Language
DR DINESH RAMOO
Why study the Biology of Language?
1.
The study of brain regions related to language clarifies our previous
discussion of language comprehension and production. We will learn
that various aspects of our language capacity are not mere
abstractions but rather have separate and specifiable representations
in the brain.
2. The study of the biological foundations of language extends our
discussion of language acquisition. If specialized brain mechanisms
enable children to acquire language, then how much language is
possible in species such as nonhuman primates that lack these
mechanisms?
Some Basic Anatomy
NAVIGATING THE BRAIN
The Cerebrum
 Consists of two cerebral hemispheres
 Left cerebral hemisphere
 Right cerebral hemisphere
 The human cerebrum is largely convoluted.
 This increases the cerebral cortex area
The Brain
Inside the Brain
Major Divisions of the Brain
Gyri and Sulci
 A gyrus (pl. gyri) is a ridge
on the cerebral cortex.
 a
sulcus (pl. sulci) is a
depression or groove in
the cerebral cortex.
 Together, these create the
folded appearance of that is
characteristic of human and
other mammalian brains.
Fissures
Deep convolutions are called fissures.
The Two Hemispheres
 Most people know that the brain is divided into two hemispheres (see Kolb & Whishaw, 2009).
 The two hemispheres of the brain are partly specialized for different tasks: broadly speaking, in most
right handed people the left hemisphere is particularly concerned with analytic, time-based
processing, while the right hemisphere is particularly concerned with holistic, spatially based
processing.
 For the great majority (96%) of right-handed people, language functions are predominately localized
in the left hemisphere. We say that this hemisphere is dominant.
 According to Rasmussen and Milner (1977), even 70% of left-handed people are left hemisphere
dominant.
 This localization of function is not tied to the speech modality; imaging studies show that just the
same left-hemisphere brain regions are activated in people producing sign language with both hands
(Corina, Jose-Robertson, Guillermin, High, & Braun, 2003).
Localisation of Function
The localisation of function
 The brain is not a homogeneous mass; parts of it are specialized for specific tasks.
 How do we know this?
 Most of our early understanding about how brain and behavior are related came
from lesion studies combined with an autopsy: neuropsychologists would discover
which part of the brain had been damaged, and relate that information to behavior.
 Now we have brain imaging techniques available, particularly fMRI, which can also
be used with unimpaired speakers.
 These techniques indicate which parts of the brain are active when we do tasks such
as reading or speaking.
Phineas Gage

In 1848, during a bizarre incident at the
construction site of a Canadian railroad,
Phineas Gage, one of the workers, accidentally
set off an explosion that resulted in a tamping
iron shooting up through his lower cheek and
out of the top of his head, flying 20ft in the air
before landing.

Amazingly, the heat of the bar cauterized and
therefore sealed the hole that it made in Gage‘s
head.

However, with time, this previously amiable
and reliable man became quite unreliable,
made very bad judgments(e.g. he managed to
ruin himself financially) and seemed to lose
social skills.

A neurologist, Harlow (1868) suggested that
the damage to Phineas Gage‘s brain had
disrupted his abilities to plan and to maintain
socially accepted behaviour.
Isolating Functional Areas of the Brain
Paul Broca
Karl Wernicke
Isolating Functional Areas of the Brain
Karl Wernicke
Paul Broca

In 1861 Broca treated a man who became known as ‗Tan‘ (Broca,
1861/1965).Following a stroke(the bursting of a blood vessel in the
brain), Tan had great difficulty making intelligible utterances.

In 1874 Wernicke, was working with patients that exhibited the reverse of
Tan‘s pattern of behavioural problems (Wernicke, 1874).

Thus, they appeared to be able to speak fluently. They produced whole words
in continuous speech that sounded superficially at least like full sentences –
but had difficulties in understanding what was said to them.

Although, on the surface, their speech seemed fluent, on closer examination it
was found to contain many errors(such as neologisms) and was very difficult
to comprehend.

At most, he could produce only a few syllables at any one time, and
nothing that sounded like real connected language.

In spite of his profound inability to produce intelligible language –
his aphasia –Tan was able to understand fully what was said to him.

Broca proposed that a part of Tan‘s brain was damaged that was
responsible for coordinating the muscle movements required for
speech.

Wernicke proposed that his patients had sustained damage to an area
responsible for storing the sound patterns of words, resulting in their
difficulties in comprehending speech.

Post-mortem analysis of Tan‘s brain revealed what Broca had
suspected –that damage to Tan‘s brain was localized to a particular
area.

Post-mortem examination of one of his patients showed a clear specific area
of damage, in the temporal lobe and slightly further back in the brain than
Broca‘s area.
The Earliest Known Case
―…He is speechless. An ailment not to be cured.‖
Edwin Smith Papyrus (case 20)
This is probably the earliest recorded instance of language difficulties
caused by traumatic brain injury.
Brain Mechanisms and Language
 Some of the most significant insights into the biological foundations of language
have come from individuals who have suffered damage to portions of the brain
regions associated with language functions.
 These unfortunate individuals typically display uneven patterns of language
behavior, with some functions spared and others dramatically impaired or even
eliminated.
 A language disorder produced by brain damage is called an aphasia.
 As you might imagine, these ‗‗experiments of nature‘‘ vary tremendously in terms of
the exact site of the brain damage and the corresponding behavioral patterns.
 Nevertheless, we begin by examining some of the more common types of aphasia.
Broca‘s Aphasia
 The disorder Broca‘s aphasia, also known as
expressive aphasia, was discovered by and
named after the French surgeon Paul Broca.
 Broca studied individuals who, after a stroke
or accident, were often unable to express
themselves by more than a single word at a
time.
 Although nouns and verbs were usually well
preserved, they tended to omit articles,
conjunctions, and grammatical inflections.
 This pattern of speech is referred to as
agrammatism and is revealed in the following
excerpt, in which a patient is attempting to
explain that he came to the hospital for dental
surgery:
Yes . . . ah . . . Monday . . . er . . . Dad and Peter
H . . . (his own name), and Dad . . . er . . .
hospital . . . and ah . . . Wednesday . . .
Wednesday, nine o’clock . . . and oh . . .
Thursday . . . ten o’clock, ah doctors . . . two . . .
an’ doctors . . . and er . . . teeth . . . yah.
(Goodglass & Geschwind, 1976, p. 408)
The Diagnosis
 The clear difficulty in articulating speech by Broca‘s aphasics might lead us to believe that its
agrammatic nature is due to a voluntary economy of effort.
 That is, because articulation is so difficult—they speak slowly and often confuse related
sounds—perhaps Broca‘s aphasics are trying to save effort by expressing only the most
important words.
 Although this factor may have some role in the disorder, it is not the most important
feature, because many Broca‘s aphasics do no better after repeated efforts at self-correction.
 Moreover, the writing of these patients is usually at least as impaired as their speech, and
individual words out of grammatical context are usually spared.
 These considerations suggest that the main feature of this disorder is the loss of the ability
to express grammatical relationships, either in speech or in writing.
Broca‘s Area
 Broca‘s area is adjacent to the motor cortex and
part of the frontal lobe, which is intimately
involved in processes such as thought,
reasoning, judgment, and initiative.
 Broca's area is made up of Brodmann areas 44
(pars opercularis) and 45 (pars triangularis).
 In recent years, we have learned that the brain
regions involved in Broca‘s aphasia are
somewhat larger than those initially identified
by Broca and accepted over the years (Naeser,
Palumbo, Helm-Estabrooks, Stiassny- Eder, &
Albert, 1989).
 Nonetheless,
the important point for our
purpose is that this somewhat larger Broca‘s
area is distinguishable from brain regions
serving other language functions.
Wernicke‘s Aphasia
 A few years after Broca‘s discovery, a young
surgeon named Carl Wernicke discovered a
different form of aphasia.
 It results from damage to a region in the left
temporal lobe near the auditory cortex.
 This region is now called Wernicke‘s area.
 Wernicke‘s
aphasia, which is sometimes
called receptive aphasia, is associated with
speech that is fluent but of little informational
value, which is known as paragrammatic
speech.
 Here is an example:
Well this is . . . mother is away here working
her work out o’ here to get her better, but when
she’s looking, the two boys looking in the other
part. One their small tile into her time here.
She’s working another time because she’s
getting, too.
(Goodglass & Geschwind, 1976, p. 410)
Diagnosis
 comprehension is also impaired. It is interesting to note, however, that
Wernicke‘s aphasics appear to perceive phonemes in a manner similar
to normal individuals (Blumstein, Baker, & Goodglass, 1977), and they
also show evidence of semantic priming (Blumstein, Milberg, & Shrier,
1982; Milberg & Blumstein, 1981).
 This would suggest that sentence- and/or discourse-level processing
deficits might figure into the comprehension problems of Wernicke‘s
aphasics.
Wernicke‘s Area
 Wernicke's area is classically located
in the posterior section of the
superior temporal gyrus (STG) in the
(most commonly) left cerebral
hemisphere.
 This area encircles the auditory cortex
on the lateral sulcus (the part of the
brain where the temporal lobe and
parietal lobe meet).
 This
area is neuroanatomically
described as the posterior part of
Brodmann area 22.
Hand Gestures

Both Broca‘s and Wernicke‘s aphasia are associated with
deficits in the hand gestures that typically accompany speech,
but in different ways.

Two kinds of gestures appear in normal speech (Bavelas et al.,
1992; McNeill, 1985):
 those that refer to some aspect of the content of the
conversation and
 those that appear to be more interactive in nature.

An example of the former type, a referential gesture, would be
to raise one‘s hand and point upward to signify upward
movement.

An illustration of an interactive gesture is putting one‘s hand
up as a means of indicating that one‘s turn is not finished.
Broca‘s aphasics tend to have impairments in the second type
of gesture; Wernicke‘s aphasics have more problem with the
first type (Ciccone, Wapner, Foldi, Zurif, & Gardner, 1979).
Conduction Aphasia
 Conduction Aphasia A third major type of aphasia is conduction
aphasia, which is a disturbance of repetition.
 Individuals with conduction aphasia appear to be able to understand
and produce speech but have difficulty in repeating what they have
heard.
 Geschwind (1965) attributes this form of aphasia to a disconnection
between Broca‘s and Wernicke‘s areas, although other interpretations
are possible (Damasio & Damasio, 1989).
Major Aphasic Syndromes
Syndrome
Behavioural Deficit
Lesion Site(s)
Broca‘s Aphasia
Disturbance of speech production;
agrammatic speech; relatively good
comprehension and naming
Frontal lobe adjacent to primary motor
cortex
Wernicke‘s Aphasia
Disturbance in auditory
comprehension; fluent speech
Posterior portion of first temporal gyrus
Conduction Aphasia
Disturbance of repetition and
spontaneous speech
Lesion in arcuate fasciculus and/or
other connections between frontal and
temporal lobes
Transcortical Sensory Aphasia
Disturbance of single word
comprehension with relatively
intact repetition
Connections between parietal and
temporal lobes
Transcortical Motor Aphasia
Disturbance of spontaneous speech,
with sparing of naming
Subcortical lesions in areas underlying
motor cortex
Anomic Aphasia
Disturbance of production of
single words
Various parts of parietal and temporal
lobes
Global Aphasia
Major disturbance of all
language functions
Large portions of association cortex
Biological Models of Speech Production
Geschwind Model for Speech Production
 Geschwind
(1972) described how language
generation flows from areas at the back to the
front of the left hemisphere.
 When
we hear a word, information is
transmitted from the part of the cortex
responsible for processing auditory information
to Wernicke‘s area.
 If we then speak that word, information flows to
Broca‘s area where articulatory information is
activated, and is then passed on to the motor
area responsible for speech.
 If the word is to be spelled out, the auditory
pattern is transmitted to a structure known as
the angular gyrus. If we read a word, the visual
area of the cortex activates the angular gyrus
and then Wernicke‘s area.
Speaking
Major Areas in Language Comprehension
 Wernicke’s area plays a central role in language comprehension.
 Damage to the arcuate fasciculus results in difficulties repeating language,
while comprehension and production remain otherwise unimpaired. This
pattern is an example of a disconnection syndrome.
 Disconnection occurs when the connection between two areas of the brain is
damaged without damage to the areas themselves.
 The angular gyrus plays a central role in mediating between visual and
auditory language.
Limitations of the Geschwind Model

This model is now known to be too simple for several reasons (Kolb & Whishaw, 2009; Poeppel & Hickok, 2004).

Although for most people language functions are predominantly localized in the left hemisphere, they are not restricted to it. Some important language functions
take place in the right hemisphere.

Some researchers have suggested that the right hemisphere plays an important role in an acquired disorder known as deep dyslexia, that it carries out important
aspects of visual word recognition, and that it is involved with aspects of speech production, particularly prosody (regarding the loudness, rhythm, pitch, and
intonation of speech); see Lindell (2006) for a review.

Subcortical regions of the brain might play a role in language. For example, Ullman et al. (1997) found that although people with Parkinson‘s disease (which
affects subcortical regions of the brain) could successfully inflect irregular verbs (presumably because these are stored as specific instances rather than generated
by a rule), they had difficulty with regular verbs, suggesting that subcortical regions play some role in rule-based aspects of language.

However, subcortical damage is usually also accompanied by cortical damage (e.g., see Olsen, Bruhn, & Öberg, 1986), and diseases such as Parkinson‘s leads to
damage to the cortical regions of the brain to which these subcortical regions project, so claims that subcortical regions play a critical role in language need to be
treated with some caution. The right cerebellum becomes significantly activated when we process the meaning of words (Marien, Enggelborghs, Fabbro, & De
Deyn, 2001; Noppeny & Price, 2002; Paquier & Marien, 2005; Petersen, van Mier, Fiez, & Raichle, 1998).

Even within the left cortex it is clear that brain regions outside the traditional Wernicke–Broca areas play an important role in language. In particular, the whole
of the superior temporal gyrus (of which Wernicke‘s region is just part) is important.

Brain damage does not have such a clear-cut effect as the model predicts. Complete destruction of areas central to the model rarely results in permanent aphasias
of the expected types.
Lateralisation of Language Processes
THE TWO HEMISPHERES
There has been a great deal of
interest in the functions of the
left and right hemispheres of the
brain in recent decades, and
part of that interest extends to
the lateralization of language
functioning.
The term lateralization refers to
the tendency for a given
psychological function to be
served by one hemisphere, with
the other hemisphere either
incapable or less capable of
performing the function.
Split-brain Research

A consistent finding in the research on aphasia is that language deficits
are associated with damage to the left hemisphere of the brain more
often than to the right hemisphere.


In one, a patient was shown a picture of a spoon in her left visual
field and was asked what she saw.
Moreover, we have known for some time, from studies of animals, that
communication between the hemispheres may be disrupted by severing
the corpus callosum.

She replied, ‘‘No, nothing.’’ Then she was asked to select with her left
hand the object from an array that was out of sight, and she correctly
picked out the spoon from a group of common objects.

In the animal studies, one hemisphere could be taught a specific task,
and then the other hemisphere could be tested.


Typically, little or no learning was found in the other hemisphere,
indicating little or no transfer of information between the hemispheres
following severing of the corpus callosum.
When asked what she was holding, she responded, ‘‘Nothing.’’ When
asked to reach for the object with her right hand, she performed at a
chance level, as likely to pick up a straw or a pencil as a spoon
(Sperry, 1968).

These results may be interpreted in light of the way information gets processed
by the two hemispheres.

When a stimulus is presented to the left visual field, the right hemisphere of a
split-brain patient becomes aware of the stimulus and is able to communicate
that awareness in nonverbal ways, such as grabbing an object with the left hand,
which is controlled by the right hemisphere.

Because speech is predominantly controlled by the left hemisphere, the patient
is unable to describe what she has seen.

Moreover, the right hand is incompetent to find the correct object because the
left hemisphere does not ‗‗know‘‘ what the object is.



In the 1940s, these two lines of research converged in a dramatic way
with the emergence of the split-brain operation. In this operation, human
patients had their corpus callosum severed as a means of preventing the
spread of epilepsy from one side of the brain to the other.
The earliest reports (see Springer & Deutsch, 1998) gave little indication
of what was to come. The patients‘ everyday behavior was virtually
unaffected, and postsurgical testing revealed no obvious deficits. The
surgery, by the way, produced relief from epileptic seizures in some
patients but not others.
We are now in position to examine some of the studies of split-brain
patients.
Visual Pathways
 When fixating on a point, each eye sees both
visual fields but sends information about the
right visual field only to the left hemisphere
and information about the left visual field
only to the right hemisphere.
 This crossover and split is a result of the
manner in which the nerve fibers leading
from the retina divide at the back of each eye.
 The
visual areas of the left and right
hemisphere normally communicate through
the corpus callosum.
 If the callosum is cut and the eyes and head
are kept from moving, each hemisphere can
see only half of the visual world.
Lateralisation
 Studies of split-brain patients clarify the respective roles of the left and right hemispheres in the use of language.
The left hemisphere is more linguistically sophisticated than the right, especially in the areas of syntactic and
phonetic processing.
 The right hemisphere is more adept at understanding the multiple meanings of ambiguous words and in
comprehending pragmatic aspects of language such as indirect speech acts.
 Studies of dichotic listening with normal individuals typically reveal right-ear advantages for speech stimuli and
left-ear advantages for non-speech stimuli.
 Nevertheless, speech sometimes elicits left-ear advantages, and right-ear advantages for musical stimuli have
been found. The distinction between holistic and relational processing appears to capture a salient difference in
how the two hemispheres do their work.
 Lateralization is not limited to humans or even to primates. Japanese macaque monkeys show lateralization of
species-specific vocalizations, and anatomical arrangements in songbirds are analogous to those in humans.
 This evidence suggests that human lateralization for speech is part of a larger evolutionary pattern.
Genetic Factors
INNATENESS OF LANGUAGE
The Language Acquisition Mechanism
• Learning spoken language is different from other types of learning in
that it does not require instruction.
• Reading and writing however require specific instruction to be learnt.
• This indicates that language acquisition is a biologically determined
phenomenon.
Is language acquisition innate?
Genetic Basis of Language

Forkhead box protein P2 (FOXP2) is a protein that, in
humans, is encoded by the FOXP2 gene, also known as
CAGH44, SPCH1 or TNRC10, and is required for
proper development of speech and language.

Initially identified as the genetic factor of speech
disorder in KE family, its gene is the first gene
discovered associated with speech and language.

The gene is located on chromosome 7 (7q31, at the
SPCH1 locus), and is expressed in fetal and adult
brain, heart, lung and gut.

In humans, mutations of FOXP2 cause a severe speech
and language disorder.

Versions of FOXP2 exist in similar forms in distantly
related vertebrates; functional studies of the gene in
mice and in songbirds indicate that it is important for
modulating plasticity of neural circuits.
Summary
 Different language skills involve different parts of the brain. Individuals who have
sustained brain damage often show deficits only in selected aspects of language.
 Studies of split-brain patients and normal individuals reveal that the left
hemisphere of the brain controls language, especially syntactic processes and
language production, for most people. The right hemisphere is essentially mute but
plays a role in comprehension and in the pragmatic aspects of language.
 Although they do not use language in their natural environment, chimpanzees can
be taught sign language. The degree of similarity between chimpanzee language and
child language is a matter of considerable debate.
 Studies of the evolution of language have examined gestures, brain specialization,
and vocal tract specialization in nonhuman primates. Fossil records of vocal tract
anatomy suggest that the capacity for speech is a recent evolutionary development.
Questions?