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BRAIN LATERALIZATION LANGUAGE AND COGNITION

BRAIN LATERALIZATION LANGUAGE AND COGNITION. CEREBRAL LATERALIZATION. Significant Events in History Marc Dax (1836) Dax was the first to report left hemisphere involvement in speech disorders caused by brain damage. Paul Broca (1860’s)

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BRAIN LATERALIZATION LANGUAGE AND COGNITION

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  1. BRAIN LATERALIZATIONLANGUAGE AND COGNITION

  2. CEREBRAL LATERALIZATION • Significant Events in History • Marc Dax (1836) • Dax was the first to report left hemisphere involvement in speech disorders caused by brain damage. • Paul Broca (1860’s) • Unaware of Dax’s work, Broca made key discoveries regarding left hemisphere involvement in aphasia. • Broca’s area, Broca’s aphasia • Hugo-Karl Liepmann (1900’s) • Apraxia is almost always caused by left hemisphere damage.

  3. CEREBRAL LATERALIZATION • Assessments of Lateralization • Sodium Amytal Test • Dichotic Listening Test  • Functional Brain Imaging

  4. CEREBRAL LATERALIZATION • Speech lateralization and handedness • The left hemisphere is dominant for speech in majority, both right- and left-handed, although greater variability among left-handed individuals. • Neurological studies of aphasics (Russell & Esper, 1961). • Right handed aphasics: 60% left, 2% right hemisphere damage • Left handed aphasics: 30% left, 24% right hemisphere damage • Results of Sodium amytal tests (Milner, 1974). Left-hemisphere dominance for speech in: • 92% of right-handed individuals • 69% of left-handed or ambidextrous individuals • 30% of left-handed or ambidextrous individuals with early left hemisphere damage

  5. CEREBRAL LATERALIZATION • Sex Differences and Lateralization • Some evidence suggests that the male brain is more lateralized than female brain. • e.g., McGlone’s (1977, 1980) studies of unilateral stroke victims and WAIS subscore tests • Some fMRI studies show that females tend to use both hemispheres in language-related tasks more so than males.

  6. SPLIT-BRAIN STUDIES • Meyers’ and Sperry’s work in cats • Split-Brain Patients • Commisurotomy to reduce seizure spreading. • Tests involving verbal identification of stimuli presented to the left or right hemisphere. • Tests involving spatial stimuli presented to L or R hemisphere.

  7. Myers and Sperry (1953)

  8. Testing Split-Brain Patients

  9. HEMISPHERIC SPECIALIZATIONS • Examples of Lateralization • Left Hemisphere Specializations • Language • Controlling ipsilateral movement • Right Hemisphere Specializations • Spatial ability • Emotion • Musical ability

  10. NEUROANATOMICAL ASSYMETRY • Planum Temporale • Larger in left hemisphere in most individuals • Geschwind and Levitsky (1968) study • Witelson (1983) study • Asymmetry is present at infancy • Asymmetry of planum temporale in chimps and other apes • Left planum temporale and perfect pitch

  11. APHASIA • Definition: Acquired disorders of language secondary to brain damage • Common Subtypes • Broca’s aphasia • Wernicke’s aphasia • Global Aphasia • Conduction Aphasia

  12. LANGUAGE AREAS

  13. BROCA’S APHASIA • Characteristic symptoms • labored and poorly articulated speech • agrammatism (telegraphic speech) • anomia • agraphia (writing impairment) • Region of brain damage • left inferior frontal cortex, 3rd frontal gyrus, anterior to face region of motor cortex (Broca’s area)

  14. WERNICKE’S APHASIA • Characteristic symptoms • poor comprehension of spoken and written language • fluent and spontaneous speech, but incoherent • paraphasia (sound and word substitutions) • alexia (reading impairment) • Region of brain damage • left superior temporal gyrus (Wernicke’s area)

  15. GLOBAL APHASIA • Characteristics • Total loss of comprehension and expressive abilities, involving both spoken and written language. • Some automatic speech, such as emotional exclamations retained • Damage is extensive • involves both B. and W. areas, large portions of frontal, temporal and parietal cortex.

  16. CONDUCTION APHASIA • Characteristics • fluent speech, comprehension only slightly impaired • repetition primarily impaired (esp. novel or nonwords, or sentences) • Brain regions damaged • arcuate fasciculus (connection between B and W area) • or primary auditory cortex

  17. APHASIAS: SUMMARY

  18. APHASIAS: SUMMARY

  19. WERNICKE-GESCHWIND MODEL Connectionist Model for the anatomical analysis of aphasias

  20. DYSLEXIA • Developmental Dyslexias • Some controversy in categorizing this disorder • Sensory-processing problem? • Memory disorder? • Acquired Dyslexias • surface dyslexia (whole word reading impaired) • deep dyslexia (phonological dyslexia)

  21. NEURAL ABNORMALITIES IN DYSLEXIA • Anomalies in cortical cell arrangement • Ectopias: unusual groupings of cells in outer layers • Micropolygyria: excessive cortical folding • Disoriented cells • These abnormalities probably occur during neural migration during fetal development

  22. BRAIN IMAGING DYSLEXIA • fMRI studies show different patterns of brain activation in dyslexics and nondyslexics. • Dyslexic subjects: • showed less activation in posterior regions (e.g. Wernicke’s area) and overactivity in anterior regions compared to nondyslexics. • showed less activation of visual cortex in response to written words.

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