Brain And Aphasia

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Brain And Aphasia

  1. 1. The Neuroscience of LanguageFrom Structure to Process
  2. 2. Neuroscience and Language• Aphasia (or dysphasia) – Language disorder of auditory or oral speech, writing (agraphia), or reading (alexia) produced by injury to brain areas specialized for these functions
  3. 3. Nature’s Experiments
  4. 4. Nature’s Experiments • Stroke – Status post 5 hours
  5. 5. Nature’s Experiments• Status post 5 days.
  6. 6. Blood-Brain Barrier • Blood is toxic to neurons. – Makes evolutionary sense. – Insulates brain from what’s in the blood.
  7. 7. Paul Broca • Broca (1865) described patients who displayed halting, agrammatic speech – Content words were well preservedPaul Broca1824-1880 – Function words (i.e., adjectives, articles) impaired
  8. 8. Broca’s Aphasia• Patient “Tan”• Brain tumor in Left frontal brain region• Broca: Lesion disrupted speech
  9. 9. Broca’s Aphasia• Broca’s Aphasia – Damage to “motor images”• Language comprehension skills relatively preserved• Typically observed in patients with damage to left inferior prefrontal cortex
  10. 10. Broca’s Aphasia• “Yes… ah… Monday… er… Dad and Peter H… (patient’s 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
  11. 11. Carl Wernicke • Wernicke (1874) described patients whose speech is fluent, but has no informational value
  12. 12. Wernicke’s Aphasia• Neologisms• Speech appears to have no information content• “fluent nonsense”• Preserved function words, impaired content words• Comprehension impaired• Even simple sentences not well understood• Associated with left temporal lobe damage
  13. 13. Wernicke’s Aphasia• “Well this is… mother is away here working her work out o’here to get her better, but when she’s looking in the other part. One their small tile into her time here. She’s working another time…” Goodglass & Geschwind, 1976
  14. 14. Articulatory Auditory speechspeech “memories” “memories” Geschwind 1979 Scientific American
  15. 15. Articulatory Auditory speechspeech “memories” “memories” Production Comprehension problems problems + empty error-filled production
  16. 16. Broca’s aphasia Wernicke’s aphasia Production Comprehension problems problems + empty error-filled production
  17. 17. Lichtheim• Lichtheim (1885) – cases of patients able to understand and produce speech but unable to repeat words• “Conduction aphasia”• Hypothesis: Broca’s area (speech production) and Wernicke’s area (speech comprehension) intact
  18. 18. Conduction aphasia Error-filled speech, but good comprehensionBroca’s aphasia Wernicke’s aphasia Production Comprehension problems problems + empty error-filled production
  19. 19. Broca’s, Wernicke’s Area, and Connections• Lichtheim’s (1885) and Geschwind’s (1965) model• Auditory input mediated by Wernicke’s area• Motor output mediated byBroca’s area• Regions connected by arcuate fasciculus
  20. 20. Wernicke-Lichtheim “House” Model Concept representations C Widely distributed! M AMotor word images Auditory word images Broca’s area Wernicke’s area
  21. 21. Lichtheim/Geschwind Model Association Cortex ConceptsVentral prefrontal Posterior Temporalcortex Motor word Auditory word Cortex Comprehension Arcuate Comprehension Fasciculus Speech motor output Auditory input
  22. 22. Lichtheim/Geschwind Model Concepts Association Cortex XVentral prefrontal Posterior Temporalcortex Motor word Auditory word Cortex Comprehension Arcuate Comprehension Fasciculus Speech motor output Auditory input Broca’s Aphasia
  23. 23. Lichtheim/Geschwind Model Concepts Association Cortex XVentral prefrontal Posterior Temporalcortex Motor word Auditory word Cortex Comprehension Arcuate Comprehension Fasciculus Speech motor output Auditory input Wernicke’s Aphasia
  24. 24. Lichtheim/Geschwind Model Concepts Association Cortex XVentral prefrontal Posterior Temporalcortex Motor word Auditory word Cortex Comprehension Arcuate Comprehension Fasciculus Speech motor output Auditory input Conduction Aphasia
  25. 25. More aphasias!Aphasia type Production Comp Repetition C1. Broca’s Non-fluent Good Poor 5 4 1 22. Wernicke’s Fluent, Poor Poor paraphasic M 3 A3. Conduction Fluent, Good Poor paraphasic 7 84.Transcortical Fluent, Poor Goodsensory paraphasic5.Transcortical Terse, Good Goodmotor echolalic6. Global Poor Poor Poor7. Aphemia Dysarthric Good Limited only by dysarthria8. Pure word Normal Very poor! As Very poordeafness if deaf!
  26. 26. Problems• Models assumed to map directly onto underlying brain structures• However, patients described as “Broca’s aphasics” had lesions in other areas• Inadequate psychological concepts – e.g., “loss of motor images”
  27. 27. Broca’s Aphasia• Damage to Broca’s area alone is not enough to produce Broca’s aphasia• Usually involves Broca’s area + surrounding areas including M1 & insula.
  28. 28. Wernicke’s Aphasia• Damage to Wernicke’s area alone is not enough to produce Wernicke’s aphasia• Usually involves Wernicke’s area + surrounding areas including MTG & angular gyrus.
  29. 29. Conduction Aphasia Common area?• Damage to the arcuate fasciculus has not been associated with conduction aphasia• Usually two lesion patterns: posterior STG (wernicke’s areas) and/or SMG
  30. 30. Transcortical Sensory Aphasia Common area?• Variable lesion patterns, mostly posterior to Wernicke’s area• Deficit tends to be transient evolving into anomic aphasia
  31. 31. Transcortical Motor Aphasia•Damage often anterior and/or superior to Broca’s area
  32. 32. Global Aphasia• Tend to be large “peri-Sylvian” lesions• But smaller lesions can also cause global aphasia
  33. 33. Aphemia• Damage to lower motor cortex
  34. 34. Pure Word Deafness• Damage to STG bilaterally is the most common pattern, although small left subcortical lesions have also been documented.
  35. 35. Neuropsychology Methods• Early neuropsychology (Broca, Wernicke, Luria, et al.) made inferences based largely on associations – Identify a group of patients with fairly homogeneous functional impairment – fairly homogeneous physical impairment – Identify a “syndrome”
  36. 36. Problems• Absence of rigid quantitative methodology of the day• Patients not always carefully described
  37. 37. Resurgence of Neuropsychology in the 1960s• Renewed interest in using neuropsychological cases to draw inferences about neural substrata of cognition• More powerful inferential methods• Emphasis on – Single case studies – Modern quantitative methods
  38. 38. Neuropsychology Methods• Modern neuropsychology (e.g., Warrington, McCarthy, Farah)• Study single cases or groups with homogeneous physical impariment• Focus on dissociations
  39. 39. Neuropsychology Methods• Single dissociation• Patient with lesion in brain region A• Performs well on task A• Performs poorly on task B• Inference: brain region A mediates performance on task B but not task A
  40. 40. Neuropsychology Methods• Problems with single dissociations• Does not rule out other interpretations• Patient may suffer some global deficit (e.g., general cognitive resource) that Task A does not require (e.g., because it is easier)• Thus, performance differences between Tasks A and B may reflect task difficulty, not the function of Brain Region A
  41. 41. Neuropsychology Methods• Double dissociation• Patient with lesion in brain region A performs well on Task A and poorly on Task B• Patient with lesion in brain region B performs well on Task B but poorly on Task A• Inference: Brain region A mediates Task B Brain Region B mediates Task A
  42. 42. Neuropsychology Methods• Since subjects are “equated” for damage, “global deficit” argument circumvented• Tasks may be assumed to be modular, depending on separate neural processes or resources
  43. 43. Brain Imaging • We now have techniques that allow us to visualize the structure and function of the brain.
  44. 44. MRI• MRI of a typical brain.
  45. 45. PET • Typical brain visualized with Positron Emission Tomography.
  46. 46. Functional Neuroimaging - time (seconds) Deoxy Oxy• Functional magnetic resonance imaging
  47. 47. Functional Neuroimaging Passive word viewing -Activates visual areas -Particularly Left Occipital Cortex Passive word listening -Activates auditory areas -Words (not nonwords) particularly Left Temporal Cortex (Wernicke’s area)• Petersen et al., 1988 PET study
  48. 48. Functional Neuroimaging Repeating words -Bilateral activation of motor and Sensory face areas -No Activation of Broca’s or Wernicke’s Verb Generation -e.g., Cake  “Eat” - Left Frontal Lobe Activation (Broca’s Area)• Confirms neuropsychology research
  49. 49. What Have we Learned?• What does localization tell us? – Where processing is occuring. – What is connected to what. – How many parts there are. – What happens when one part gets damaged.• We’d like to know more.
  50. 50. What Would we Like to Know?• How the parts work. – What are the rules and representations that are involved with language processing? – What is the nature of the processing that is taking place. • Digital/discrete/autonomous • Analog/continuous/integrated
  51. 51. ERP studies• Semantics – N400• Syntax – LAN – P600/SPS
  52. 52. N400 (2)
  53. 53. P600
  54. 54. Haagort et al. (2003)Het vrouwtje veegde de vloer met een oude bezem gemaakt van twijgen (Thewoman wiped the floor with an old broom made of twigs).*Het vrouwtje veegde de vloer met een oude kliederde gemaakt van twijgen (Thewoman wiped the floor with an old messed made of twigs).
  55. 55. P600 can serve as an index of frequency of a construction• The captain liked the crew was unhappy• The captain heard the crew was unhappy• The captain believed the crew was unhappy• A P600 was strongest in the first sentence, present in the second sentence, and not present in the third sentence.• Larger P600 for syntactically complex sentences (Kaan et al., 2002).
  56. 56. Correct: De houthakker ontweek de schroef op dinsdag (The lumberjack dodged thepropellor on Tuesday).Weak violation: *De houthakker ontweek de schroeft op dinsdag (The lumberjackdodged the propelled on Tuesday).Strong violation: *De houthakker ontweek de omdat op dinsdag (The lumberjackdodged the because on Tuesday).
  57. 57. Combining methods
  58. 58. Summary• The Wernicke-Geschwind model is being replaced by new models.• New models focus on both neural basis and timing of language comprehension, and have moved beyond simplistic divisions of comprehension/production.

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