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 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 functions Locating 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 – Auditory M – Motor B – 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 – Conceptual M – Motor T – Tactile V - Visual Each node in this diagram represents the cardinal node of a subweb of properties T

Distributed Representation: A “Functional Web” V C Each node in this diagram represents 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 features V

Add phonological recognition node V M C For example, FORK Labels for Properties: C – Conceptual M – Motor P – Phonological image T – Tactile V – Visual T P The phonological image of the spoken form [fork] (in Wernicke’s area)

Add node in primary auditory area V M C T 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 – Conceptual M – Motor P – Phonological image PA – Primary Auditory T – Tactile V – Visual

Add node for phonological production V M C T P PA Pr For example, FORK Labels for Properties: C – Conceptual M – Motor P – Phonological image PA – Primary Auditory Pr – Phonological production T – Tactile V – Visual Articulatory structures (in Broca’s area) that control articulation of the spoken form [fork]

Add node for phonological production V M C T P PA PP For example, FORK Labels for Properties: C – Conceptual M – Motor P – Phonological image PA – Primary Auditory PP – Phonological Production T – Tactile V – Visual Arcuate fasciculus

Some of the cortical structure relating to fork V MC T 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 symptoms with areas of lesion Broca’sBroca’s area Wernicke’sWernicke’s area Conduction SMG, Insula, Arcuate fasciculus Transcortical motor Areas anterior and/or superior to Broca’s area Transcortical sensory Areas 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 – Tactile C – Conceptual PP – Phonological Production PR – Phonological Recognition PA – Primary Auditory V – Visual The (bidirectional) link from form to meaning

Form and Meaning V PR PA 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

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