dominant hemisphere identification handedness tells us
TRANSCRIPT
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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
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Language Processing
• Speaking a written word involves at least five neocortical areas. Each area performs certain functions
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Brain areas involved in Language
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Visual Pathway
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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?
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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
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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
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Tapping during nursery rhyme
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Laterality of Auditory Processing
Selectively deliver to one hemisphere but suppressing ipsilateral pathway
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Monoaural vs Dichotic Listening
•With dichotic input the ipsilateral ear’s input is suppressed.
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Left ear advantage for melodies, right ear advantage for shadowing spoken letters
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Dichotic Listening Results
• 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
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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
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Hemisphericity
• Does one hemisphere dominate individual’s cognition or cognitive style?
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Street Test of Right Hemisphere Dominance
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Mooney (1957) – ID age & gender
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Left hemisphere dominance
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Similarities Test (selected items)
• Orange
• Coat
• Wagon
• Wood
• Egg
• Poem
• Fly
• Banana
• Dress
• Bicycle
• Alcohol
• Seed
• Statue
• Tree
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Thompson, Bogen, Marsh, 1979
• Industrial cultures LH>RH
• Non-industrial cultures RH>LH
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Gazzaniga’s Interpreter Model
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LECTURE 7Homotopic Callosal Connections
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Equipotentiality hypothesis vs homotopic principle
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EEG site pairings
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Callosal Connections
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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).
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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.
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Principle of Homotopy
Four types of cortico-cortical projections:
1) homotopic, 2) homoareal, 3) heterotopic, and 4) ipsilateral
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
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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.
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Callosal Function Models
• 1. Transfer of information
• 2. Inhibition of opposite side processing
• 3. Homotopic inhibition, generating complementary percepts
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Conduction Time
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Conduction Time in Split Brains
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Anatomical asymmetry
• LH contains – more gray matter
• Larger cells and greater cell density (but not all areas), more nonmyelinated fibers esp. frontally, suggesting more localized, more serial processing
• RH contains– More white matter
• more myelinated axons to link different brain regions
– slightly larger and heavier than LH
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Cell Density differencesHuman SMG (posterior language areas)
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Larger LH pyramidal cells in Superior Temporal Gyrus
• HOWEVER asymmetry is not found in nearby angular gyrus
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Homotopic inhibition theory
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• Priming explained
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LECTURE 8Functional Dichotomies
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Aphasia by handedness & hemisphere damaged
• Right handed: LH 60%, RH 2%
• Left handed: LH 32%, RH 24%
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Split Brain PatientsSplit Brain Patients
PREOPERATIVE
POSTOPERATIVE
RIGHT HANDLEFT HAND
RH superiority onBlock design
RH superiority onDrawing tasks
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Local-global stimuli used to investigate hierarchical representation
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Facilitatory effect for global-local stimuli
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STUDY INTACT BRAINS
Visual Laterality Method
• Tachistoscopic presentation (less than 200 ms)– Lateralized stimulus exposure– Compare performance LVF vs. RVF presentations.– Dependent variables: reaction time, accuracy
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Methodology Issue
• 2 @ 2 = 3 or 4
• 2 @ 3 = 6 or 8
• 2 @ 4 = 8 or 16
• Analysis of correct responses only
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Functional DichotomiesBlackburn Intellectual Sensuous
Oppenheimer Time, History Eternity, Timelessness
Levy, Sperry Analytic Gestalt
Bogen Propositional Appositional
Luria Sequential Simultaneous
Semmes Focal Diffuse
I Ching The Creative: Heaven,Masculine, Yang
The Receptive: Earth,Feminine, Yin
Many sources Verbal Spatial
Many sources Intellectual Intuitive
Jung Causal Synchronicity
Bacon Argument Experience
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• Left Hemisphere• Verbal• Sequential, temporal,
digital, routinized• Logical, analytic• Familiar• Propositional
• Right Hemisphere• Nonverbal,
visuospatial• Simultaneous, spatial,
analogical, parallel, integrative
• Gestalt, holistic, synthetic
• Novelty• Appositional
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