Ch. 16 Split Brain
what have studies suggested about the planum temporale?
Schlaug and colleagues found that musicians with perfect pitch appear to have a larger planum temporale in the left hemisphere than do non musicians and musicians without perfect pitch. Furthermore, in musicians, having a larger planum temporale is positively correlated with their ability to hear poorly pronounced syllables. (determined by MRI)
what other animal have they found similar results in?
Split brain monkeys; there could not perform fine tactual discrimination tasks, like rough versus smooth, or fine motor responses, like unlocking a puzzle, with one hand if they had originally learned it with the other, provided that they are not allowed to watch their hands.
How has the split brains ability to perform separate functions been demonstrated on tests of attention?
Split brain patients are able to identify specific objects among an assortment of objects more quickly than control patients. This is because each hemisphere are able to maintain an independent focus of attention and are making two independent searches at once.
recap: what is the broca's area and where is it located?
The Broca's area is located in the inferior portion of the left prefrontal cortex and is the center for speech production
what is the predominant theory of language localization?
The Wernicke-Geschwind model
what is the helping hand phenomenon? Give an example.
The helping hand phenomena is a result of one hemisphere thinking that the other is making an error, thus correcting its behavior. If a patient were flashed an orange to their right visual field/left hemisphere and a pencil to the left visual field/right hemisphere, and the patient were presented with a table IN OPEN VIEW of an assortment of objects and asked to pick the objects it saw, the RIGHT hand would reach for an orange and the left hand, thinking an error was occurring (because it saw the pencil) would reach out and REDIRECT the right hand to pick up the pencil.
which hemisphere is superior at controlling ipsilateral movement?
The left hemisphere! When one hand is moved, activation is observed in the contralateral hemisphere, but its also activated some in the ipsilateral hemisphere, as well. More activation is seen ipsilaterally in the left hemisphere than in the right. When the left hemisphere gets lesions, it is more likely that there will be reduced accuracy in the left hand than would be seen in the right hand if the right hemisphere had a lesion.
Which hemisphere is superior at spatial ability?
The right hemisphere! When subjects were presented with an object in their left and right hand and they tactually examined the object, they were asked to point out which 3D block would look like the one they examined if it were made of cardboard and unfolded. right hemisphere superiority was noticed during this task. Furthermore, each hemisphere approached the task differently. the right hemisphere/left hand examines the object silently and rapidly, whereas the right hand/left hemisphere is hesitant and verbally describes the object throughout examination (not by choice of the patient). Results are consistent with other studies, such as on contralateral neglect (caused by damage to the right hemisphere)
what is wernicke's area and where is it located?
The wernicke's area, discovered by Carl Wernicke, is a language area located in the left temporal lobe just posterior to the primary auditory cortex (so, in the left planet temporale). This area is a SECOND language area - specifically, the cortical area of language COMPREHENSION.
what has been noted about asymmetrical differences in the cortical language areas of the brain respective to language lateralization in the left hemisphere?
There is a correlation between the anatomical and functional asymmetries - a correlation between the degree of anatomical lateralization in a person and the degree of language lateralization in that same person, but 90% of healthy people are left hemisphere dominant for language, while only (and no more than) 65% of healthy people have anatomical biases for the three cortical language areas, creating reason for skepticism. in short, many anatomical asymmetries have been noted between hemispheres, but few have been correlated with functional asymmetries.
how can the left and right hemisphere find ways to communicate with one another?
They can either communicate neurally via indirect pathways through the brain stem, OR they can communicate via an external route called cross-cuing.
What were sperry and gazzaniga's experiment on split brain patients?
They could not cut the optic chiasm in split brain humans because it would cause a scotoma. instead, they told patients to fixate on the center of the display screen and an image flashed on both the left and right side of the screen for 0.1 seconds, to prevent confounding eye movement between images. The stimuli presented to the patients left visual field went to their right visual cortex and vice versa.
what is the motor theory?
This theory suggests that the left hemisphere is specialized not for the control of speech specifically but for the control of fine movements, with speech being only one example. This theory comes from studies that lesions that produce aphasia often produce other motor deficits.
what is the analytic-synthetic theory?
This theory suggests that there are two basic modes of thinking: analytical and synthetic. The left hemisphere is postulated to be involved in analytical modes of thinking, operating in a logical and computerlike fashion, analyzing and attaching verbal labels. The right hemisphere is postulated to be a synthesizer, organizing and processing information in terms of gestalts (wholes).
what hemisphere typically takes dominance in split brain patients and what happens when there is conflict over dominance?
Usually the left hemisphere takes control of every day tasks and behaviors of a split brain patients. But, in some patients (Peter), the right hemisphere fights for control by doing things to annoy the left hemisphere, such as not walking in the intended direction or turning off the tv while the left hemisphere is enjoying a show. Sometimes the left hemisphere swears at the left hand and sometimes strikes it out of frustration, or uses the right hand to try to control the left hand.
what is broca's aphasia?
Wernicke suggested that selective lesions of Broca's area produce a syndrome of aphasia whose symptoms are EXPRESSIVE - characterized by NORMAL comprehension of written and spoken language and by speech that retains its meaningfulness despite being slow, labored, disjointed, and poorly articulated.
How do split brain patients participate in visual completion?
When split brain patients are presented with a composite of two separate half faces side by side and are asked to focus on the center of the display screen, and are then asked to point out what they saw among an assortment of complete faces, the left hemisphere will say that it saw a completed version of what was flashed to the right visual field. Even when asked a leading question, such as "did you notice anything unusual about what you saw?", the left hemisphere will describe a completed version of the face presented to the right visual field. This test is called the Chimeric Figures Test, presented to patients by Levy, Travarthen,, and Sperry.
Can the two different hemispheres perform different functions at the same time? If so, give an example.
Yes! If you flash two different images to each hemisphere at the same time, such as an orange and a pencil, and ask the patient to reach into two separate bags, one with each hand, and pull out the objects each hemisphere saw, they will pull out an orange and a pencil! but before the hands pull out the objects, if you ask the patient what they are about to pull out, the patient will say "two oranges", because the left hemisphere saw an orange. The left hemisphere will be confused when it sees that there is an orange AND a pencil!
What is the z lens and who created it?
Zaidel (in 1975) created a lens that he named the z lens. It is a contact lens that is opaque on one side and, because it is a contact, moves with the eye, preventing visual information from entering into more than one hemisphere at a time (the other eye is completely covered). This lens was created so patients could focus on stimuli for more than 0.1 seconds, allowing them to perform more various tests to compare the ability of the right versus left hemisphere.
what is global aphasia?
a severe disruption of all language related abilities
the planum temporale
an area of the temporal lobe cortex. lies in the posterior reign of the lateral fissure; thought to play a role in the comprehension of language and is often referred to as the WERNICKE'S AREA
what was the wernicke-geschwind model originally based off of?
case studies of patients with strokes, tumors, and penetrating brain injuries
so for redundancy, what is the left angular gyrus responsible for?
comprehending language related visual input
what is conduction aphasia?
conduction aphasia is a THIRD type of aphasia that is a result of damage to the pathwas CONNECTING the brooks and wernicke's areas (the arcuate fasciculus). in this aphasia, comprehension nd spontaneous speech is intact, but patients have trouble REPEATING words they just heard.
what test showed support to the left hemisphere being the interpreter of the brain?
controls (normal brains) and split brain patients were tasked with guessing between whether a top light or bottom light would come on net int he sequence. The top light was programmed to come on 80% of the time in a random sequence, but participants were unaware of this information. control subjects attempted to guess a pattern thus did not always guess the top light, resulting in a 68% correct rate. in split brain patients, the left hemisphere acted the same as the controls and tried to interpret some deeper meaning to the sequence, resulting in a poor performance. In contrast, the right hemisphere alone always guessed the top light, thus performed best on the activity.
what was the myers and sperry experiment?
experimenters cut through the cats corpus callosum and optic nerve (because visual information can travel contralaterally through both of these routes) and put an eye patch over one eye of the cat, cutting of the ipsilateral visual information for that eye. Each cat was then confronted with two panels, one with a circle and one with a square. The positions of the circle and square varied by trial. The cats had to learn which symbol to press in order to get food. this method allowed them to test one hemisphere at a time in the cats.
what is one form of information that appears to be readily passed between hemispheres?
feelings of emotion! in one study, patients were presented with emotionally loaded images to the right hemisphere and the left hemisphere was asked to respond verbally to the images. The left hemisphere responded with the correct emotional response, even though it was unaware of the image.
what were the results of the second phase of the myers and sperry experiment?
in the second phase, the eye patch was transferred to the other eye. Transferring the patch had NO effect on cats with EITHER a cut corpus callosum or a cut optic chiasm and control cats, BUT it had a devastating effect on the experimental cats (where both were cut). The performance of the experimental cats dropped immediately to 50% correct responses and the cats had to relearn the task as if they had never seen it before.These results suggested that the hemispheres have the capacity to act as two separate brains and the CC's job is to transfer info between them.
are broad clusters of abilities (i.e., spacial ability, language ability) lateralized or are individual cognitive processes lateralized?
individual cognitive processes are more likely to be lateralized than are broad clusters of abilities. It would not make sense to assume that language is lateralized in the left hemisphere when the right hemisphere has shown evidence of involvement in speech perception and understanding word meaning. Thus, cognitive psychologists are breaking down complex cognitive tasks, such as reading, judging space, and remembering, into their constituent cognitive processes to determine laterality.
what are the limitations of the motor theory?
it does not suggest WHY motor function became lateralized in the first place
what are the limitations of the analytic-synthetic theory?
it is too vague. It is not possible to specify the degree to which any task requires either analytic or synthetic processing, so it has been difficult to subject this theory to empirical tests. Pop psychology loves the theory.
Why did therapeutic commisurotomies come about?
it was known that seizures spread from one hemisphere to the other through the corpus callosum. It was thought that maybe if they cut the corpus callosum, but left other commisures in tact, seizures would be reduced because they would stay in their original hemisphere rather than spread. This was a great success, with with many patients never again experiencing a major convulsion. This was only to be done in patients as a last resort for severe cases.
what would happen if an object is flashed to a patients left visual field?
it would be sent to the right hemisphere and patients might say that they saw nothing at all, because the LEFT hemisphere is talking! and the RIGHT hemisphere has seen the stimulus! If you place an object in their left hand, they can identify what the object is by tactual senses, but they cannot TELL you, but the right hemisphere/left hand can reach for the correct object.
what would damage to the Broca's area cause?
it would cause damage to speech production WITHOUT causing deficits in language comprehension.
what is the difference between language lateralization and cerebral localization of language?
language lateralization refers to the relative control of language-related functions by the left and right hemispheres; language LOCALIZATION refers to the location WITHIN the hemispheres of the circuits that participate in language related activities.
the Heschl's gyrus
located in the temporal lobe cortex in the lateral fissure just anterior to the planum temporale in the temporal lobe; location of the primary auditory cortex
what specific ability do humans have over nonhumans and why?
nonhumans can interpret a wide variety of sounds but they cannot produce a wide variety of sounds, suggesting that they do not have the fine motor control to do so that humans have. This suggest that humans may have evolved from a competence in comprehension of sounds already existing our primate ancestors.
what is the problem with brocas aphasia and wernickes aphasia?
patients don't have PURE Brocas or wernickes aphasia; the damage is never totally expressive or totally receptive.
why is the wernicke-geschwind model problematic?
patients with aphasia often have very diffuse brain damage, making it hard to locate particular cortical language areas. It is also too simplistic!
How does the Broca's area work?
programs of articulate are stored in the Broca's area and speech is produced when these programs activate the adjacent area of the pre central gyrus, which controls the muscles of the face and oral cavity.
how did the results prove similar and different from test on laboratory animals?
similarly, split brain patients' hemispheres acted independently of one another, each having its own stream of consciousness, abilities, memories, and emotions. In contrast, the hemispheres were far from equal in their ability perform certain tasks. For instance, the left hemisphere is capable of SPEECH, whereas the right hemisphere is NOT.
What is another factor that contributes to hemispheric independence?
task difficulty. simple tasks are processed best by the hemisphere specialized for that task, but complex tasks are performed better by the cognitive power of BOTH hemispheres.
which hemisphere shows superiority pertaining to emotion?
the Right! unilateral brain lesion studies show that the right hemisphere is better at accurately identifying facial expressions of emotions, but fmri studies have not provided unambiguous evidence of this as of yet.
what is the difference in methodology between cognitive neurospychologists and the creators of the wernicke-gechwind model?
the WG model studies brain damaged patients whereas cognitive nps study healthy volunteers.
the frontal operculum
the area of the frontal lobe cortex that lies just in front of the face Rea of the primary motor cortex; in the Broca's area of the left hemisphere
what is the left angular gyrus?
the area of the let temporal and parietal cortex just posterior to wernicke's area. This gyrus is another cortical area implied in language.
what is the largest cerebral commissure and how many axons is it made of?
the corpus callosum; 200 million axons
alexia
the inability to read
agraphia
the inability to write
what can the left hemisphere do and not do?
the left hemisphere is verbally adept, receives sensory information from the right visual field and RIGHT hand, and controls the fine motor responses of the right hand.
if an apple is shown in a split brain patients right visual field, how can the patient communicate that they saw an apple?
the left hemisphere of the patient can either TELL the experimenter that they saw an apple, or, since the left hemisphere control the right hand, the patients right hand could reach under a ledge and feel the presented objects and pick out an apple. OR, if the apple is placed in the patients hand, the patient can either tell the experimenter that it is an apple, or place the apple down and pick out another apple from the hidden table of objects.
where are the seven components of the wernicke-geschwind model located?
the left hemisphere!
what did Joseph Jules dejerine notice about his patient with Alexia and agraphia?
the patient could not read or write but he could comprehend speech and speak. This patient had damage in the pathways connection the visual cortex and the left angular gyrus, concluding that the left angular gyrus is responsible for comprehending language related visual input
what can the right hemisphere do and not do?
the right hemisphere understands a few simple instructions but CANNOT speak; receives sensory information from the left visual field and left HAND, and who controls the fine motor responses of the LEFT HAND.
which hemisphere is superior in music ability?
the right hemisphere! the right hemisphere was better at correctly identifying melodies when different melodies were presented to each eat at the sam time and participants were tasked with identifying the two melodies heard by each ear out of various other melodies. The right hemisphere/left ear was better at identifying the melody. This is consistent with right temporal lobe lesions having a greater likelihood of disrupting music discriminations than left lesions.
what is the linguistic theory?
this theory contrast the analytic-synthetic theory and the motor theory because it believes that language IS the primary specialization of the left hemisphere, not a secondary result. This theory comes from studies of deaf people who use ASL and who suffer from unilateral brain damage. Left hemisphere damage can disrupt the production of ASL but it does not prohibit pantomime gestures, suggesting that the fundamental specialization of the LH is language. Think of the case of W.L., who experienced aphasia for ASL.
what is the motor theory of speech perception?
this theory proposes that the perception and comprehension of speech depends on the words activating the same neural circuits in the motor system that would have been activated if the listener had said the words. This theory came into light thanks to the discovery of mirror neurons, in which neurons fire when particular responses are either performed or observed. researchers have observed over fMRI that the motor cortex is particularly active during the perception of conversational exchange. However, case studies of patients with damage to their motor cortex have not shown the predicted deficits in speech perception.
what is wernicke's aphasia?
wernicke suggested that selective lesions of the WERNICKES area are RECEPTIVE - characterized by POOR comprehension of both written and spoken language and speech that is MEANINGLESS but still retains the superficial structure, rhythm, and intonation of normal speech. This normal sounding but nonsensical speech is known as WORD SALAD.
do neuropsychologists still diagnose brocas aphasia or wernickes aphasia?
yes, but with the understanding that it is much less selective than originally thought and much more diffuse and variable.
What is the cognitive approach of the left hemisphere?
"the interpreter" - a hypothetical neuronal mechanism that continuously assesses patterns of events and tries to make sense of them.
what are the two survival advantages of cereal lateralization?
1. Much like having one highly skilled hand is better than having two moderately skilled hands, having a higher concentration of neurons that perform similar function in one hemisphere is advantageous. 2. two different kinds of cognitive processes may be more readily performed simultaneously if they are lateralized to different hemispheres.
what two observations did the experiment of Myers and Sperry lead to?
1. The corpus callosum transfers learned information from one hemisphere to the other; 2. when the CC is cut, each hemisphere can act independently of the other, as if there are two brains
what three categories do cognitive neuropyshcologists divide analysis of constituent cognitive processes into?
1. phonological analysis: analysis of sound of language 2. grammatical analysis: analysis of the structure of language 3. semantic analysis: analysis of the meaning of language
what are seven components of the wernicke-geschwind model?
1. primary visual cortex 2. angular gyrus 3. primary auditory cortex 4. wernicke's area 5. arcuate fasciculus 6. broca's area 7. primary motor cortex
what two pieces of evidence DO support parts of the wernicke-geschwind model?
1. the Brocas and wernickes area DO play an important role n language - many aphasics have diffuse cortical damage that involves one or both areas 2. there is a tendency for anterior damage to involve deficits that are more expressive and posterior damage to evolve deficits that are more receptive
what are three theories for the evolution of cerebral lateralization/asymmetry?
1. the analytic-synthetic theory 2. the motor theory 3. the linguistic theory
to determine inter hemispheric differences in the brain, what three cortical language areas have been most focused on (due to their importance in language, the most lateralized of all cognitive abilities)?
1. the frontal operculum 2. the planum temporale 3. the Heschl's gyrus
what are the difficulties in studying anatomical asymmetry in the three language areas?
1. their boundaries are unclear; there is no clear consensus as to how to best define them 2. there are large differences among healthy people in the structure of these cortical language areas
recap: what are the five methods for studying cerebral lateralization?
1. unilateral lesions 2. the sodium amytal test 3. the dichotic listening test 4. fmri 5. split brain patients
What is an example of cross-cuing?
In one experiment researchers wanted to see if the left hemisphere could correctly report colors flashed to the left visual field. they presented the left visual field with two colors: red or green. At first, the left hemisphere had a 50% correct rate, indi
What is an example of cross-cuing?
In one experiment researchers wanted to see if the left hemisphere could correctly report colors flashed to the left visual field. they presented the left visual field with two colors: red or green. At first, the left hemisphere had a 50% correct rate, indicating that it was guessing at the correct answer. However, over time, this performance improved appreciatively, suggesting that information was somehow being transferred to the left hemisphere. BUT it turned out that this was not the case: instead, when the right hemisphere saw green and the left hemisphere guessed red, the right hemisphere gave physical CUES to the left hemisphere that red was wrong, such as by frowning and initiating a head shake. This caused the left hemisphere to change its answer to green.
what were the results of the first phase of the myers and sperry experiment?
In the first phase, the experimental cats learned the discrimination task as easily as the control cats, despite having a scotoma (area of blindness) from the optic chiasm being cut. This result suggested that one hemisphere alone could work as effectively and rapidly as two together.
how would the RIGHT hemisphere indicate that object that had previously been shown to the LEFT hemisphere?
It couldn't. The left hand could make a random guess but it would not know which object had been shown.
tests on what function led tot he discovery that cognitive abilities are similar in both hemispheres, just expressed differently?
Memory! the left hemisphere performs better on some tests of memory while the right hemisphere performs better on others tests of memory. The left hemisphere appears to be specialized for encoding episodic memory and it appears to be better at remembering verbal material, whereas the right hemisphere is better at remembering nonverbal material.
what has festival language suggested about human ancestors?
Monkeys communicate with some vocalization but mostly with specific hand gestures used in a variety of ways to act as language. their hand gestures are more like language than their vocalization, suggesting that maybe primate gestures have been a critical stag in the evolution of human language
is there a substantial difference between functions in each hemisphere?
NO! the media often makes this portrayal, but we have found that there is only slight differences in performance of function per hemisphere, as in, a slight bias toward one hemisphere or the other. The differences are not absolute. There is overlap in each hemisphere! For example, there is substantial language related activity in the right hemisphere, with the left only having a slight advantage over the right (55 to 45% advantage in the dichotic listening test).
what have surgeons found from removing the brocas area and large parts of the wernickes area without removing large amounts of cortical tissue?
No lasting speech or language-related problems were noted after a few weeks
is complete hemispherectic independence an inevitable consequence of split brain surgery?
No! in MOST split brain patients, it is possible to have some communication passed between hemispheres, depending on: 1. the particular surgery 2. the time since surgery 3. the particular info 4. the method of testing
Is the usefulness of the z lens limited to visual tests?
No! it has also been used to study the left and right hemispheres abilities to comprehend speech. Because each ear presents to each hemisphere, it is impossible to present spoken words to only ONE hemisphere. To correct for this, Zaidel uses the z lens by giving patients a oral direction to follow (Such as put the f=green square under the red circle), then the right hemisphere alone is presented with the colored token while the task is being completed.
is cerebral lateralization exclusive to humans?
Nope! Cerebral lateralization has been noticed in other vertebrates and invertebrates long before human existence. There is also a preference for right-handedness/sidedness in fish, reptiles, birds, amphibians, and mammals, probably from an evolutionary result of feeding preference. Animals also show left hemisphere language lateralization.
Does electrical stimulation of the cortex provide any support for the wernicke-geschwind model?
Nope! Language is disrupted far beyond the areas addressed in the model AND people have major differences in the organization of their language abilities. Language is widely distributed among areas of the cortex.
