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Dominant Hemisphere Identification

Dominant Hemisphere Identification. Handedness tells us likelihood of LH being dominant (i.e., location of speech center) 96% in right handers 70-85% in left handers Behavioral tests Functional neuroimaging Clinical tests – Wada, TMS. Language Processing.

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Dominant Hemisphere Identification

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  1. Dominant Hemisphere Identification • Handedness • tells us likelihood of LH being dominant (i.e., location of speech center) • 96% in right handers • 70-85% in left handers • Behavioral tests • Functional neuroimaging • Clinical tests – Wada, TMS

  2. Language Processing • Speaking a written word involves at least five neocortical areas. Each area performs certain functions

  3. Brain areas involved in Language

  4. Visual Pathway

  5. Lateralized Eye Movements • Three synonyms for walking or intelligence • Define impish or prudish • Which direction does Thomas Jefferson face on the nickel? • Which states share a border with North Carolina?

  6. Lateralized Eye Movements – Interpreting LEMs • Leftward movement from viewer’s perspective indicates LH activation (RVF squashed as LH taxed) • Rightward mvt = RH location of function

  7. Gross Laterality Tests • Comparative (primary) tasks • Differences to lateralized presentations • Accuracy and reaction time to emotional matching, abstract words, etc • Competitive (secondary) tasks • Finger tapping during math, emotion, language tasks • Dowel balancing task

  8. Tapping during nursery rhyme

  9. Selectively deliver to one hemisphere but suppressing ipsilateral pathway Laterality of Auditory Processing

  10. Monoaural vs Dichotic Listening • With dichotic input the ipsilateral ear’s input is suppressed.

  11. Left ear advantage for melodies, right ear advantage for shadowing spoken letters

  12. Right Ear Adv Digits Words Nonsense syllables Morse code Pitch changes in Thai by Thais Voicing & Place Difficult rhythms Ordering temporal information Backward speech Left Ear Advantage Melody Musical chords Environment Sounds Emotional Sounds Prosody Complex Pitch changes No advantage Rhythms Vowels Dichotic Listening Results

  13. Dichotic Listening in Unusual Cases • Genie (neglected/linguistically deprived) shows a left ear (RH) advantage for words • Right hemispherectomy show normal right ear (LH) advantage for syllables • Split brains show normal right ear advantage for digits

  14. Hemisphericity • Does one hemisphere dominate individual’s cognition or cognitive style?

  15. Street Test of Right Hemisphere Dominance

  16. Mooney (1957) – ID age & gender

  17. Left hemisphere dominance

  18. Orange Coat Wagon Wood Egg Poem Fly Banana Dress Bicycle Alcohol Seed Statue Tree Similarities Test (selected items)

  19. Thompson, Bogen, Marsh, 1979 • Industrial cultures LH>RH • Non-industrial cultures RH>LH

  20. Gazzaniga’s Interpreter Model

  21. LECTURE 7Homotopic Callosal Connections

  22. Equipotentiality hypothesis vs homotopic principle

  23. EEG site pairings

  24. Callosal Connections

  25. Principle of Callosal Homotopy • The general principle of callosal homotopymthat the corpus callosum unites "corresponding and identical regions" (Meynert, 1872, p. 405), was initially proposed by Arnold (1838-1840) in his anatomy tables and later popularized by Meynert (1872). • Bruce (1889-1890) criticized Meynert's endorsement, calling it speculation and opinion, ungrounded in physiological fact. • Bremer (1958), however, continued to advance this principle, based on the anatomical and electro-physiological research of his day (Curtis, 1940a,b).

  26. Principle of Callosal Homotopy • CITATIONS • Arnold, F (1838-1840). Tabulae anatomicae. London: Black & Armstrong. • Bremer, F. (1958). Physiology of the corpus callosum. Research Publications for the Assessment of the Nervous and Mental Disability, 36, 424-428. • Bruce, A. (1889-1890). On the absence of the corpus callosum in the human brain, with description of a new case. Brain, 12, 171-190. • Curtis H.J. (1940a). Intercortical connections of > corpus callosum as indicated by evoked potentials. Journal of Neurophysiology, 3, 407-413 • Curtis H.J. (1940b). An analysis of cortical potentials mediated by the corpus callosum. Journal of Neurophysiology, 3, 414-422. • Meynert T (1872). The brain of mammals. In S. Stricker (Ed.) Manual of human and comparative histology, Vol II, (pp 367-537). London: The New Syndenham Society.

  27. Principle of Homotopy Arnold (1838-1840) – Anatomical tables – first mention of callosal homotopic connectivity Myers (1850s) – popularized homotopic principle Bremer (1956) – “general principle of homotopy” based on Curtis (1940;1944) electrophysiological studies Four types of cortico-cortical projections: 1) homotopic, 2) homoareal, 3) heterotopic, and 4) ipsilateral

  28. Reciprocity in Callosal Connections • Representation of the reciprocity of callosal connections: strong homotopic connectivity, and wherever there is heterotopic connections, there is normally ipsilateral connections to the same areas.

  29. Callosal Function Models • 1. Transfer of information • 2. Inhibition of opposite side processing • 3. Homotopic inhibition, generating complementary percepts

  30. Conduction Time

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