Chapter 16 -Lateralization, Language, and the Split Brain Flashcards
Broca’s discoveries
–Aphasia
– Inferior left prefrontal lobe
Liepmann
–Apraxia
Broca’s Area
The location of Broca’s area: in the inferior left prefrontal cortex, just anterior to the face area of the left primary motor cortex.
Aphasia
brain damage–produced deficit in the ability to produce or comprehend language.
apraxia
is almost always associated with left-hemisphere damage, despite the fact that its symptoms are bilateral (involving both sides of the body). Patients with apraxia have difficulty performing movements when asked to perform them out of context, even though they often have no difficulty performing the same movements when they are not thinking about doing so
cerebral dominance
According to this theory, one hemisphere—usually the left—assumes the dominant role in the control of all complex behavioral and cognitive processes, and the other plays only a minor role. This thinking led to the practice of referring to the left hemisphere as the dominant hemisphere and the right hemisphere as the minor hemisphere.
sodium amytal test is a
test of language lateralization (Wada, 1949) is often given to patients prior to neurosurgery
sodium amytal test involves
the injection of a small amount of sodium amytal into the carotid artery on one side of the neck. The injection anesthetizes the hemisphere on that side for a few minutes, thus allowing the capacities of the other hemisphere to be assessed. During the test, the patient is asked to recite well-known series (e.g., letters of the alphabet, days of the week, months of the year) and to name pictures of common objects. Then, an injection is administered to the other side, and the test is repeated.
dichotic listening test is
noninvasive; thus, it can be administered to healthy individuals.
Tests of Cerebral Lateralization
Sodium amytal test •Dichotic listening test •Functional brain imaging
Brain damage data
60% dextrals have aphasia –30% sinestrals left handers
left hemisphere is dominant
for language-related abilities in almost all dextrals and in the majority of sinestrals.
Discovery of the Relation Between Speech Laterality and Handedness
About 92% right-handed subjects are left-hemisphere
dominant for speech
–About 69% of left-handed and ambidextrous are left-hemisphere dominant for speech
–Early left-hemisphere damage may cause right-hemisphere dominance for speech
Sex Differences in Brain Lateralization
male victims of unilateral strokes were three times more likely to suffer from aphasia than female victims
Myers and Sperry Experiment
- Help to define the role of the corpus callosum
- 1953 by an experiment on cats
Myers and Sperry Experiment - conclusions
Forebrains are independent for learning and memory
▪ Corpus callosum carries information between hemispheres
▪ Best study method is to limit information to a single hemisphere
Commissurotomy in Humans with Epilepsy - Procedure to test hemispheric independence
Visual stimuli flashed to left or right fixation point –Tactual information presented to “blind” hand –Require verbal or manual response
Commissurotomy in Humans with Epilepsy - conclusions
Confirm independent streams of consciousness –Left hemisphere could speak, right could not
Vogel and Bogen,
to initiate a program of commissurotomy for the treatment of severe intractable cases of epilepsy—despite the fact that a previous similar attempt had failed, presumably because of incomplete transections
The therapeutic benefits of commissurotomy turned out
to be even greater than anticipated: Despite the fact that commissurotomy is performed in only the most severe cases, many commissurotomized patients do not experience another major convulsion.
Evidence That the Hemispheres of Split-Brain Patients Can Function Independently - left
Object presented to left hemisphere
–By touching with right hand or viewing in right visual field ▪ Subject could pick out the correct object with right hand
▪ Could name correct object
▪ Could not pick out the correct object with left hand
Evidence That the Hemispheres of Split-Brain Patients Can Function Independently - right
Object presented to right hemisphere
–By touching with left hand or viewing in left visual field ▪ Subject could pick out the correct object with left hand
▪ Claimed nothing had been presented
▪ Could not pick out the correct object with the right hand
Cross-Cuing
Communication across hemispheres by a non- neural route
The “Helping-hand” phenomenon
A subject observes their own Left hand pointing to an object (in response to what was seen by the Rt. Hemisphere) & changes/guides the movement with their Rt. Hand so that it points to (or agrees with) what was seen by the Left Hemisphere.
Doing Two Things at Once
Helping-hand phenomenon • Split-brain patients can learn two things at once • Example • Helping-hand phenomenon • Visual completion • Chimeric figures test
