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Last Lecture

Last Lecture. Dichotic Listening The corpus callosum & resource allocation Handedness Broca’s Aphasia. This Lecture. Wernicke’s aphasia The Wernicke-Geschwind Model Category-specific semantic deficits and the representation of meaning Introduction to the Frontal Lobes.

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Last Lecture

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  1. Last Lecture • Dichotic Listening • The corpus callosum & resource allocation • Handedness • Broca’s Aphasia

  2. This Lecture • Wernicke’s aphasia • The Wernicke-Geschwind Model • Category-specific semantic deficits and the representation of meaning • Introduction to the Frontal Lobes

  3. Remember the Wernicke-Geschwind model? • Broca’s area: forms detailed coordinated plans for language production (speech, writing, covert/rehearsal) • Explains dysfluency and poor articulation in Broca's aphasics. Butcomprehension is not perfect... • Poor syntax comprehension • Broca's aphasics poor at judging grammaticality Active: The horse kicked the cow. Passive: The cow was kicked by the horse.

  4. Agrammatism • Disproportional difficulty reading and producing function words. • Difficulty using & understanding grammar Modification to Wernicke-Geschwind model Broca's area: • Plan for coordinating language production • Understanding and using syntax.

  5. Wernicke's aphasia Examiner: Can you tell me a little bit about why you’re here? Patient: Sine just don’t know why, what is really wrong, I don’t know, cause I can eaten treffren eatly an everythin like that I’m all right at home. (Excerpt from Kertesz, 1980; quoted by Carlson, 1994)

  6. Symptoms of Wernicke's aphasia • Speech: phonetically & grammatically normal but meaningless. • generally fluent, unlabored, well articulated. • normal intonation (prosody). • words used inappropriately • nonsense words (neologisms) --> "word salad" • meaning expressed in roundabout way (circumlocution). • Comprehension: severely impaired.

  7. According to Wernicke-Geschwind model Wernicke's Area ... • DOES NOT STORE MEANING! • stores memories of sound sequences that constitute words. • translates auditory input into phonological forms that can then access semantics.

  8. Interpretation of Wernicke's area in action Understanding spoken language: • Primary auditory cortex (41/42) -> Wernicke's A. (22) -> semantic networks distributed throughout the brain. Spontaneous speech: "cognitive" areas send input to Wernicke's area: • Cognition -> Wernicke's A. (22) -> arcuate fasciculus -> Broca's A. (44)-> Primary motor cortex

  9. PET activation during listening

  10. According to the Wernicke-Geschwind model... Wernicke’s A. essential for reading... Visual processing --> Angular g. --> Wernicke's a.--> Semantics • Angular gyrus (39) translates visual code to a form accessible by Wernicke’s a. • grapheme --> phoneme translation • Wernicke’s a. translates to a form that can access meaning. • Implication: Reading requires phonological recoding via Wernicke’s A.

  11. Where is meaning stored? • Wernicke’s area does not store meaning, so where is it stored? • Meaning is represented across a network of brain areas • Different brain areas contribute to different kinds of knowledge

  12. How do we know this? Loss of SEMANTIC KNOWLEDGE: • can’t recognize, describe from memory, or answer questions about objects. Category -specific deficits: • Some patients cannot recognize living things (plants/animals) but can recognize man-made things (tools/instruments) • Opposite pattern also reported (non-living things-impairment) Double dissociation: separable representations for difference categories of knowledge.

  13. PET evidence: Category-specific activations (Martin et al., 1996) • Subjects identified pictures of animals and tools • Certain visual areas more active for animals • Left premotor area more active for tools. Semantic representation: - tools represented by function. - living things represented by visual/sensory features.

  14. The Role of Language • Language ability sets us apart from other animals. • Is language what makes us uniquely human?

  15. Phineas Gage • Railroad worker who experienced head trauma. • He survived. • Drastically changed his personality. • “Gage was no longer Gage,” according to his friends.

  16. The Frontal Lobes Claim: The frontal lobes mediate those abilities that make us uniquely human. • Herein lies the riddle... What makes us uniquely human?

  17. The Frontal Lobes • 3 natural boundaries • posterior: central sulcus • inferior: Sylvian fissure (lateral fissure) • medial/inferior: corpus callosum

  18. Major Subdivisions Precentral (motor cortex): Area 4 Premotor: • Areas 6 and 8 (including supplementary motor) • 44 (Broca’s area) Prefrontal: • dorsolateral: Areas 46, 45, 9, 10 • ventrolateral: Areas 11, 47 • orbital: 11 Anterior Cingulate: • medial: Areas 24, 25, 32

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