Brain Damage and Locations of Linguistic Functions

1. Ling 411 – 07 Brain Damage and Locations of Linguistic Functions

2. Variability in Aphasic Symptoms

3. 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

4. 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

5. 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

6. Different Kinds of Stroke Damage • Ischemic: blockage of artery • Two sources of blockage: • Thrombosis (about 2/3 of all ischemic strokes) (B&A 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

7. 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

8. 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

9. Left hemi-sphere, showing middle cerebral artery

10. Middle Cerebral Artery www.strokecenter.org/education/ais_vessels/ais049b.html Middle Cerebral Artery, Right Hemisphere From Washington University Medical School

11. Middle Cerebral Artery Inter-Subject Variability

12. 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) Aphasic syndromes and Cerebrovascular areas

13. 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 Aphasias with middle cerebral artery occlusion

14. 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

15. Neuroanatomical correlates of the aphasiasIdentifying linguistic functionsLocating linguistic functions

16. 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

17. 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)

18. 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)

19. CT template – Conduction Aphasia (patient I)

20. CT template – Conduction Aphasia (patient II) Left auditory cortex and insula

21. MR template – Wernicke Aphasia (patient I) Poster-ior portion of super-ior and middle temp-oral gyri

22. MR template – Wernicke Aphasia (patient II) Super-ior temp-oral gyrus, AG, SMG

23. Two different patients with anomia Inability to retrieve words for unique entities Deficit in retrieval of animal names

24. Two more patients with anomia Deficit of retrieval of words for man-made manipulable objects Severe deficit in retrieval of words for concrete entities

25. 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?

26. The Wernicke-Lichtheim model (1885) A – Auditory M – Motor B – Ideation Numbers indicate areas in which disconnection would produce distinct disorder From Lichtheim 1885

27. 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

28. 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

29. 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

30. 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

31. Distributed Representation:A “Functional Web” Each node in this diagram represents the cardinal node of a subweb of properties For example, C T M Let’s zoom in on this one V

32. Zooming in on the “V” Node.. A network of visual features V FORK Etc. etc. (many layers)

33. 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 Wernicke’s area)

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

35. 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 Broca’s area) that control articulation of the spoken form [fork]

36. 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

37. Some of the cortical structure relating to fork T M C PP P V PA

38. MR template – Transcortical Sensory Aphasia AG and post-erior SMG

39. 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

40. CT template – Broca Aphasia (patient I) Superior sector of Broca’s area and the pre-motor region immedi-ately above it

41. MR template – Broca Aphasia (patient II) Most of Broca’s area, motor and pre-motor regions, white matter, insula

42. MR template – Transcortical Motor Aphasia Motor and pre-motor cortices just above Broca’s area

43. Summary: Correlations of symptomswith areas of lesion Aphasic Syndrome Area of Damage Cf. H. Damasio 1998: 43-44

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

45. 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

46. 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

47. Brain damage and localization of functionHypothetical example A function Damage

48. 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

49. 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?

50. What is it that determines location? • Logical categories like ANIMALS vs. TOOLS/UTENSILS? • If so, why? • Abstract categories based on cognitively salient properties?