Brain Damage and Locations of Linguistic Functions

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Brain Damage and Locations of Linguistic
Functions
Ling 411 07
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Variability in Aphasic Symptoms
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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

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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

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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

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Different Kinds of Stroke Damage

• Ischemic blockage of artery
• Two sources of blockage
• Thrombosis (about 2/3 of all ischemic strokes)
  (BA 64)
• 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
• Hemorrhagic bleeding into cerebral tissues
• Variation in location and extent of hemorrhage

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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

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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

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Left hemi-sphere, showing middle cerebral artery
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Middle Cerebral Artery
www.strokecenter.org/education/ais_vessels/ais049b
.html
Middle Cerebral Artery, Right Hemisphere From
Washington University Medical School
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Middle Cerebral Artery Inter-Subject
Variability
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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)

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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

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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

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Neuroanatomical correlates of the
aphasiasIdentifying linguistic
functionsLocating linguistic functions
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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 199825
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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)
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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)
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CT template Conduction Aphasia (patient I)
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CT template Conduction Aphasia (patient II)
Left auditory cortex and insula
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MR template Wernicke Aphasia (patient I)
Poster-ior portion of super-ior and middle
temp-oral gyri
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MR template Wernicke Aphasia (patient II)
Super-ior temp-oral gyrus, AG, SMG
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Two different patients with anomia
Deficit in retrieval of animal names
Inability to retrieve words for unique entities
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Two more patients with anomia
Deficit of retrieval of words for man-made
manipulable objects
Severe deficit in retrieval of words for concrete
entities
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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 199851)
• How to explain?

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The Wernicke-Lichtheim model (1885)
A Auditory M Motor B Ideation Numbers
indicate areas in which disconnection would
produce distinct disorder From Lichtheim 1885
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The Wernicke-Lichtheim model (1885)
Where? Brocas area Arcuate fasciculus Wernicke
s area Primary motor area and/or
subcortical Primary auditory area and/or
subcortical
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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

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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

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Concept Distributed Representation
For example, FORK Labels for Properties C
Conceptual M Motor T Tactile V - Visual
C
T
M
V
Each node in this diagram represents the cardinal
node of a subweb of properties
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Distributed RepresentationA Functional Web
Each node in this diagram represents the cardinal
node of a subweb of properties For example,
C
T
M
Lets zoom in on this one
V
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Zooming in on the V Node..
A network of visual features
V
FORK
Etc. etc. (many layers)
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Add phonological recognition node
For example, FORK Labels for Properties C
Conceptual M Motor P Phonological image T
Tactile V Visual
C
T
M
P
V
The phonological image of the spoken form fork
(in Wernickes area)
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Add node in primary auditory area
For example, FORK Labels for Properties C
Conceptual M Motor P Phonological image PA
Primary Auditory T Tactile V Visual
C
T
M
P
V
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
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Add node for phonological production
For example, FORK Labels for Properties C
Conceptual M Motor P Phonological image PA
Primary Auditory Pr Phonological production T
Tactile V Visual
C
T
M
P
Pr
V
PA
Articulatory structures (in Brocas area) that
control articulation of the spoken form fork
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Add node for phonological production
For example, FORK Labels for Properties C
Conceptual M Motor P Phonological image PA
Primary Auditory PP Phonological Production T
Tactile V Visual
C
T
M
P
PP
V
PA
Arcuate fasciculus
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Some of the cortical structure relating to fork
T
M
C
PP
P
V
PA
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MR template Transcortical Sensory Aphasia
AG and post-erior SMG
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Transcortical sensory aphasia(A. Damasio 199836)

• Fluent and paraphasic speech
• Global paraphasias
• Severe impairment in oral comprehension
• Repetition intact (unlike Wernickes aphasics)
• N.b. Refers to H. Damasio, Chapter 3, for
  localization of damage

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CT template Broca Aphasia (patient I)
Superior sector of Brocas area and the pre-motor
region immedi-ately above it
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MR template Broca Aphasia (patient II)
Most of Brocas area, motor and pre-motor
regions, white matter, insula
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MR template Transcortical Motor Aphasia
Motor and pre-motor cortices just above Brocas
area
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Summary Correlations of symptomswith areas of
lesion
Aphasic Syndrome Area of Damage
Cf. H. Damasio 1998 43-44
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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
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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
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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

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Brain damage and localization of
functionHypothetical example
A function
Damage
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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 dont know
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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?

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What is it that determines location?

• Logical categories like ANIMALS vs.
  TOOLS/UTENSILS?
• If so, why?
• Abstract categories based on cognitively salient
  properties?

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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

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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

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Two Vision Pathways (left hemisphere)
Dorsal
Where What
Ventral
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The Proximity Principle

• Closely related cortical functions tend to be in
  adjacent areas
• Brocas area and primary motor cortex
• Wernickes area and primary auditory area
• Angular gyrus and Wernickes area
• Brodmann area 37 and Wernickes area
• A function that is intermediate between two other
  functions tends to be in an intermediate location
• Wernickes area between primary auditory area
  and Angular gyrus

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Locating conceptual information three kinds of
evidence

• Proximity principle
• Brain damage
• Imaging

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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

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Nominal concepts and the proximity principle

• Supramarginal gyrus, angular gyrus, and middle
  temporal gyrus are all close to Wernickes 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

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Form (Phonological) and Meaning
The (bidirectional) link from form to meaning
T Tactile C Conceptual PP Phonological
Production PR Phonological
Recognition PA Primary Auditory V
Visual
T
C
PP
PR
PA
V
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Form and Meaning
Link from graphic form to meaning
Link from phonological form to meaning
T
C
GR Graphic Recognition
PP
GR
PR
PA
V
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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

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Proximity principle and nominal concepts

• Supramarginal gyrus, angular gyrus, and middle
  temporal gyrus are all close to Wernickes 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

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