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Lecture 14

46-256 Lecture Notes - Lecture 14: Interthalamic Adhesion, Roger Wolcott Sperry, Commissurotomy

Course Code
PSYC 2560

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December, 2 2014
Language Lateralization
Language in the Left Hemisphere
Aspects of language traditionally thought to be processed in the LH:
Split Brain Studies
Roger Sperry
Around 1960
The Nobel Prize in Physiology or Medicine 1981 (shared with Hubel and Wiesel)
Gazzaniga was one of his students
Split Brain
Treatment for medically intractable epilepsy
Cerebral commissurotomy (including anterior commisure, dorsal and ventral hippcampal
commisures, and, in some cases, the massa intermedia)
vs. Complete sectioning of corpus collosum
Contains epileptic activity to focal hemisphere
Split Brain Patients
Acute Disconnection Syndrone
episodes of intermanual conflict (see Farside Cartoon)
Alien left hand
patients sometimes report being surprised about the actions of the left hand
left-hand apraxia to verbal command
Chronic Disconnection Syndrome
indistinguishable from normals socially
inter-hemispheric transfer deficit
compensatory strategies
speaking out loud to get info to the right hemisphere
Moderate Memory Deficit
particular difficulty with uncommon paired word associates, story passages, and
acquisition of new information
tendency to confabulate
can swim, play piano, ride a bike, etc
impaired etch-a-sketch
Split Brain Experiment
“look at the dot”
Two words separated by a dot are momentarily projected.
“what word did you see?”
“point with your left hand to the word you saw”

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Conclusions from Split Brain Studies
“2 separate realms of conscious awareness; two sensing, perceiving, thinking and remembering
The RH has relatively good comprehension, but little or no production
Some patients have basic language production in RH
Theories of Cerebral Asymmetry
All purpose that it's better to have brain areas that do similar things be in the same hemisphere
Analytic-synthetic theory
2 modes of thinking, analytic (left) and synthetic (right)
Vague and essentially untestable
“the darling of pop psychology”
Motor theory
left controls fine movements – speech is just a category of movement
left damage may produce speech and motor deficits
Linguistic theory
primary role of left is language
Lateralized Functions
Right hemisphere superiority
spatial ability
musical ability
some memory tasks
Left hemisphere – superior in controlling ipsilateral movement
A More Accurate Approach to Lateralization
Broad cognitive domains are not lateralized – individual tasks may be
Better to consider lateralization of constituent cognitive processes – individual cognitive
Tests of Cerebral Lateralization
Determining which hemisphere is dominant
Sodium amytal test
Anesthetize one and check for language function
Dichotic listening
report more digits heard by the dominant half
Visual Half field presentation
Functional brain imaging
fMRI or PET used to see which half is active when doing a language test
Speech Laterality, Handedness, and Sex
Dextrals: right-handers
Sinestrals: left-handers
Left-Hemisphere dominant in almost all dextrals and most sinestrals
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