Brain Damage and

Locations of Linguistic Functions

Ling 411 – 07

Variability in Aphasic Symptoms

Why so much variation in symptoms?

Difference in areas of brain damage Difference in kinds of brain damage

•Strokes vs trauma vs infection vs tumors

•Different kinds of stroke

Anatomical variation among people•Differing cortical structures

•Differences in vascular anatomy

Difference in location of cortical functions

Why so much variation in symptoms?

Difference in areas of brain damage Difference in kinds of brain damage

•Strokes vs trauma vs infection vs tumors

•Different kinds of stroke

Anatomical variation among people•Differing cortical structures

•Differences in vascular anatomy

Difference in location of cortical functions

Different types of brain damage

Strokes, wounds, tumors, infections, degenerative disease

Each of these occurs in varying locations

Each of these has varying extent of damage

Different Kinds of Stroke Damage

1. Ischemic: blockage of artery• Two sources of blockage:

1. Thrombosis (about 2/3 of all ischemic strokes) (B&A 64)

2. Embolism: caused by a blood clot, air bubble, or detached clot

• Result: infarction – death of brain tissue that is no longer receiving blood supply

• Variation in location of blockage• Hence, variation in area of infarction

2. Hemorrhagic: bleeding into cerebral tissues• Variation in location and extent of hemorrhage

Why so much variation in symptoms?

Difference in areas of brain damage Difference in kinds of brain damage

•Strokes vs trauma vs infection vs tumors

•Different kinds of stroke

Anatomical variation among people•Differing cortical structures

•Differences in vascular anatomy

Difference in location of cortical functions

Cerebral Arteries

Anterior Cerebral Artery•Feeds frontal pole and most of the medial

surface Middle Cerebral Artery

•Feeds most of cortex, Perisylvian area Other areas

Posterior Cerebral Artery•Feeds bottom of temporal lobe and medial

surface of occipital and parietal lobes

Left hemi-sphere, showing middle cerebral artery

Middle Cerebral Artery

www.strokecenter.org/education/ais_vessels/ais049b.html

Middle Cerebral Artery, Right Hemisphere

From Washington University Medical School

Middle Cerebral Artery

Inter-Subject Variability

Aphasic syndromes and Cerebrovascular areas

Territory

•Anterior cerebral artery occlustion

•Posterior cerebral artery occlusion

•Middle cerebral artery occlusion

Aphasic syndrome

Extrasylvian motor aphasia

Occipital alexia

Various major types of aphasia (next slide)

Aphasias with middle cerebral artery occlusion

Total artery occlusion

Orbitofrontal branch

Rolandic branch

Anterior parietal branch

Posterior parietal branch

Angular branch

Posterior temporal branch

Anterior temporal branch

Global aphasia

Broca aphasia

Broca aphasia, cortical dysarthria

Conduction aphasia

Wernicke aphasia, extrasylvian sensory aphasia

Anomia, extrasylvian sensory aphasia

Wernicke aphasia

Anomia

Why so much variation in symptoms?

Difference in areas of brain damage Difference in kinds of brain damage

•Strokes vs trauma vs infection vs tumors

•Different kinds of stroke

Anatomical variation among people•Differing cortical structures

•Differences in vascular anatomy

Difference in location of cortical functions

Neuroanatomical correlates of the aphasias

Identifying linguistic functionsLocating linguistic functions

Evaluating evidence from aphasia

It would be easy if naïve localization were true• If a patient has lost an ability, then the area of

damage is the area responsible for that ability

But naïve localization is false “… language, along with other complex

cognitive processes, depends on the concerted operation of multicomponent, large-scale neural systems. The anatomical components are often widely dispersed and each acts as a partial contributor to a complicated process…”

Antonio Damasio 1998:25

Benson and Ardila on conduction aphasia

“… a single type of aphasia may have distinctly different loci of pathology. Both conduction aphasia and transcortical motor aphasia are examples of this inconsistency.” (117)

(See also p. 135)

Hannah Damasio on conduction aphasia

“Conduction aphasia is associated with left perisylvian lesions involving the primary auditory cortex…, a portion of the surrounding association cortex…, and to a variable degree the insula and its subcortical white matter as well as the supramarginal gyrus (area 40). Not all of these regions need to be damaged in order to produce this type of aphasia. In some cases without involvement of auditory and insular regions, the compromise of area 40 is extensive…. In others, the supramarginal gyrus may be completely spared and the damage limited to insula and auditory cortices … or even to the insula alone….”

(1998: 47)

CT template – Conduction Aphasia (patient I)

CT template – Conduction Aphasia (patient II)

Left auditory cortex and insula

MR template – Wernicke Aphasia (patient I)

Poster-ior portion of super-ior and middle temp-oral gyri

MR template – Wernicke Aphasia (patient II)

Super-ior temp-oral gyrus, AG, SMG

Two different patients with anomia

Deficit in retrieval of animal names

Inability to retrieve words for unique entities

Two more patients with anomia

Deficit of retrieval of words for man-made manipulable objects

Severe deficit in retrieval of words for concrete entities

More on these four anomic patients

All of these four subjects demonstrated normal concept retrieval for the concrete entities they could not name

» (Hannah Damasio 1998:51)

How to explain?

The Wernicke-Lichtheim model (1885)

A – AuditoryM – MotorB – Ideation

Numbers indicate areas in which disconnection would produce distinct disorder

From Lichtheim 1885

The Wernicke-Lichtheim model (1885)

Where?

Broca’s area

Arcuate fasciculus

Wernicke’s area

Primary motor area and/or subcortical

Primary auditory area and/or subcortical

The “C” Node

Not just in one place•Conceptual information for a single word is

widely distributed•Conceptual information is in different areas

for different kinds of concepts The second of these points and probably

also the first were already recognized by Wernicke

But.. •The diagram is nevertheless useful•There may be a single “C” (or “L”) node

anyway as cardinal node of a distributed network

Word meanings

Meaning of each word is a network Widely distributed in extrasylvian areas Conceptual and perceptual information

•Perceptual – both hemispheres Somatosensory – Parietal lobes Visual – Occipital and temporal lobes Auditory – Temporal lobes

•Conceptual More abstract (higher in network) than

perceptual Connections to perceptual information Different cortical areas for different

categories

Concept: Distributed Representation

V

M

C

For example, FORK

Labels for Properties:C – ConceptualM – MotorT – TactileV - Visual

Each node in this diagramrepresents the cardinal node of a subweb of properties

T

Distributed Representation:A “Functional Web”

V

C

Each node in this diagramrepresents the cardinal node of a subweb of properties

For example,

Let’s zoom in on this one

M

T

Zooming in on the “V” Node..

FORK

Etc. etc.(many layers)

A network of visual featuresV

Add phonological recognition node

V

M

C

For example, FORK

Labels for Properties:C – ConceptualM – Motor P – Phonological imageT – TactileV – Visual

T

P

The phonological image of the spoken form [fork] (in Wernicke’s area)

Add node in primary auditory area

V

M

CT

P

PA

Primary Auditory: the cortical structures in the primary auditory cortex that are activated when the ears receive the vibrations of the spoken form [fork]

For example, FORK

Labels for Properties:C – ConceptualM – Motor P – Phonological imagePA – Primary AuditoryT – TactileV – Visual

Add node for phonological production

V

M

CT

P

PA

Pr

For example, FORK

Labels for Properties:C – ConceptualM – Motor P – Phonological imagePA – Primary AuditoryPr – Phonological productionT – TactileV – Visual

Articulatory structures (in Broca’s area) that control articulation of the spoken form [fork]

Add node for phonological production

V

M

CT

P

PA

PP

For example, FORK

Labels for Properties:C – ConceptualM – Motor P – Phonological imagePA – Primary AuditoryPP – Phonological ProductionT – TactileV – Visual

Arcuate fasciculus

Some of the cortical structure relating to fork

V

M CT

P

PA

PP

MR template – Transcortical Sensory Aphasia

AG and post-erior SMG

Transcortical sensory aphasia(A. Damasio 1998:36)

Fluent and paraphasic speech•Global paraphasias

Severe impairment in oral comprehension

Repetition intact (unlike Wernicke’s aphasics)

N.b.: Refers to H. Damasio, Chapter 3, for localization of damage

CT template – Broca Aphasia (patient I)

Superior sector of Broca’s area and the pre-motor region immedi-ately above it

MR template – Broca Aphasia (patient II)

Most of Broca’s area, motor and pre-motor regions, white matter, insula

MR template – Transcortical Motor Aphasia

Motor and pre-motor cortices just above Broca’s area

Summary: Correlations of symptomswith areas of lesion

Broca’s Broca’s area

Wernicke’s Wernicke’s area

ConductionSMG, Insula,

Arcuate fasciculus

Transcortical motorAreas anterior and/or

superior to Broca’s area

Transcortical sensoryAreas posterior and/or superior to Wernickes

a.

Aphasic Syndrome Area of Damage

Cf. H. Damasio 1998: 43-44

Correlation of aphasia types to localization of damage

“More than 100 years of study of anatomoclinical correlations, with autopsy material as well as CT and MR scans, has proven that in spite of the inevitable individual variability, the correlation between aphasia types and locus of cerebral damage is surprisingly consistent.”

Hannah Damasio 1998: 64

Correlation of linguistic functions to localization of aphasic damage

“…the correlations per se provide only limited information about the neurobiological mechanisms of language, in health and in disease.”

Hannah Damasio 1998: 64-6

Reasoning from brain damage to localization

If area A is damaged and patient has deficit D of some function F

Does this mean that function F is subserved by area A?

Not really.. It means that A (or some portion of

A) is needed for some component of F

Brain damage and localization of function

Hypothetical example

A function

Damage

What we know so far

Conceptual information for nouns of different categories is in different locations

What defines the different categories

Where they are located

What we don’t know

Different locations for different categories

Evidence•Category dissociations in impaired patients

•Functional brain imaging

How to explain?•What are the different categories?

•Why these categories? What basis for their definitions?

What is it that determines location?

Logical categories like ANIMALS vs. TOOLS/UTENSILS?• If so, why?

Abstract categories based on cognitively salient properties?

Animals vs. Tools/Utensils?

These two categories have been studied most extensively in the literature

What is it that determines location? Observations:

•Most animals are known mostly in the visual modality

•Many tools and utensils are known largely in the somatosensory and motor modalities

We know a lot about vision from experiments

Two major components of knowing what is seen:•What?

•Where?

Where – the dorsal pathway•Parietal lobe

What – the ventral pathway•Lower temporal lobe

N.b.: These findings are consistent with the proximity hypothesis

Two Vision Pathways (left hemisphere)

Dorsal

Ventral

Where

What

The Proximity Principle

Closely related cortical functions tend to be in adjacent areas•Broca’s area and primary motor cortex

•Wernicke’s area and primary auditory area

•Angular gyrus and Wernicke’s area

•Brodmann area 37 and Wernicke’s area

A function that is intermediate between two other functions tends to be in an intermediate location•Wernicke’s area – between primary auditory

area and Angular gyrus

Locating conceptual information –three kinds of evidence

Proximity principle Brain damage Imaging

Conceptual information for nouns

Conceptual information – subnetworks• For example, DOG

Canine animal Domestic – pets Metaphoric uses Etc.

Hypothesis: cardinal concept node• Top of the hierarchical network• Ties the whole thing together

Likely locations • Angular gyrus for some• Supramarginal gyrus for some• Middle temporal gyrus for some

Nominal concepts and the proximity principle

Supramarginal gyrus, angular gyrus, and middle temporal gyrus are all close to Wernicke’s area

Angular gyrus occupies intermediate location between the major perceptual modalities

Supramarginal gyrus especially close to somatosensory perception

Middle temporal gyrus especially close to visual perception

Form (Phonological) and Meaning

V

PR

PA

T

C

PP

T – TactileC – ConceptualPP – Phonological ProductionPR – Phonological RecognitionPA – Primary AuditoryV – Visual

The (bidirectional) link from form to meaning

Form and Meaning

V

PRPA

T

C

PP

Link from phonological form to meaning

GR

GR – Graphic Recognition

Link from graphic form to meaning

Conceptual information for nouns

Conceptual information – subnetworks• For example, DOG

Canine animal Domestic – pets Metaphoric uses Etc.

Hypothesis: cardinal concept node• Top of the hierarchical network• Ties the whole thing together

Likely locations • Angular gyrus for some• Supramarginal gyrus for some• Middle temporal gyrus for some

Proximity principle and nominal concepts

Supramarginal gyrus, angular gyrus, and middle temporal gyrus are all close to Wernicke’s area

Angular gyrus occupies intermediate location between the major perceptual modalities

Supramarginal gyrus especially close to somatosensory perception

Middle temporal gyrus especially close to visual perception

end