2605_lect16.ppt

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BIOPSYCHOLOGY 8e

Topics

16.1

Cerebral Lateralization of Function

16.2

The Split Brain

16.3

Differences between Left and Right Hemispheres

16.4

Evolutionary Perspective of Cerebral Lateralization and Language

16.5

Cortical Localization of Language: Wernicke-Geschwind Model

16.6

Wernicke-Geschwind Model: The Evidence

16.7

Cognitive Neuroscience of Language

16.8

Cognitive Neuroscience of Dyslexia

Cerebral Lateralization of Function

• • •

Major differences between the function of the left and right cerebral hemispheres Cerebral commissures connect the two halves of the brain Split-brain patients have been studied to understand what happens when these connections are severed

Cerebral Lateralization of Function

Discovery of the Specific Contributions of Left Hemisphere Damage to Aphasia and Apraxia

•

Aphasia

– deficit in language comprehension or production due to brain • damage , usually on the left

Broca’s area

– left inferior prefrontal cortex, damage • leads to expressive aphasia

Apraxia

Discovery of the Specific Contributions of Left Hemisphere Damage to Aphasia and Apraxia

• Aphasia and apraxia – associated with damage to left hemisphere • Language and voluntary movement seem to be controlled by one half of the brain, usually the left • Suggests that one hemisphere is dominant, controlling these functions Copyright © Pearson Education 2011

Tests of Cerebral Lateralization

Sodium Amytal Test:

Anesthetize one hemisphere and check for language function

Functional brain imaging:

fMRI or PET used to see which half is active when performing a language test

Dichotic Listening Test:

Discovery of the Relation between Speech Laterality and Handedness

Sex Differences in Brain Lateralization Females may use both hemispheres more often for language tasks than me do (females may be less lateralized

The Split Brain

Groundbreaking Experiment of Myers and Sperry

Myers and Sperry studied split-brain cats: They transected the corpus callosum and optic chiasm so that visual information could not cross to the contralateral hemisphere. By blindfolding one eye of the cat, they restricted the visual information to the hemisphere ipsilateral to the uncovered eye.

Split-Brain Cats

• Each hemisphere can learn independently • Split-brain cats with one eye patched - Learn task as well as controls - No memory or savings demonstrated when the patch was transferred to other eye • Intact cats or those with an intact corpus callosum or optic chiasm – learning transfers between hemispheres • Similar findings with split-brain monkeys Copyright © Pearson Education 2011

Split-Brain Cats

Commissurotomy in Human Epileptics

Commissurotomy limits convulsive activity

•

Many never have another major convulsion Sperry and Gazzaniga

•

Developed procedures to test split-brain patients Differ from split-brain animals in that the two hemispheres have very different abilities – most left hemispheres are capable of speech, while the right aren’t

Commissurotomy in Human Epileptics

Evidence that the Hemispheres of Split-Brain Patients Can Function Independently

•Present a picture to the right visual field (left brain) • Left hemisphere can tell you what it was • Right hand can show you, left hand can’t •Present a picture to the left visual field (right brain) • Subject will report that he does not know what it was • Left hand can show you what it was, right hand can’t Left hemisphere can tell what it has seen, right hemisphere can only show it Copyright © Pearson Education 2011

Cross-Cuing

•

Cross-cuing – facial feedback from the other hemisphere

•

For example: the right hemisphere might make the face frown when the left hemisphere gives an incorrect spoken answer

Doing Two Things at Once

• Each hemisphere of a split-brain patient can learn independently and simultaneously •

Helping-hand phenomenon

– presented with two different visual stimuli, the hand that “knows” may correct the other •

Dual foci of attention

– split-brain hemispheres can search for target item in array faster than intact controls •

Chimeric figures task

The Chimeric Figures Test

Figure 16.6: The left hemisphere of a split-brain patient sees a single normal face that is a completed version of the half face on the right. At the same time, the right hemisphere sees a single normal face that is a completed version of the half face on the left.

The Lens

Advancing the study of split-brains with a contact lens to restrict visual input to one hemisphere

The Z Lens

• Previous studies had to limit viewing time to less than .1 second • Can be used to assess each hemisphere’s understanding of spoken instructions by limiting visual information to one side of the brain Copyright © Pearson Education 2011

Dual Mental Functioning and Conflict in Split Brain Patients

• •

Usually in split-brain patients the left hemisphere is dominant in most everyday activities For some, the right is dominant and this can create conflict between hemispheres

– –

For example, the case of Peter Hemispheres often disagreed with each other

Independence of Split Hemispheres: Current Perspective

Differences between Left and Right Hemispheres

• •

For many functions there are no substantial differences between hemispheres Key point: Lateralization of function is statistical rather than absolute

Examples of Cerebral Lateralization of Function

Left Hemisphere

•

Superior in controlling ipsilateral movement

•

An “interpreter” Right Hemisphere

•

Superior in:

•

Spatial ability

•

Emotion

•

Musical ability

•

Some memory tasks

Abilities That Display Cerebral Lateralization of Function

What is Lateralized? Broad Clusters of Abilities or Individual Cognitive Processes?

• •

Broad categories are not lateralized – individual tasks may be Better to consider lateralization of

constituent cognitive processes

– individual congitive elements

•

Example: two spatial tasks – left hemisphere is better at judging above or below, right at how close two things are

Anatomical Brain Asymmetries

• • •

Frontal operculum (Broca’s area)

•

Near face area of primary motor cortex

•

Language production Planum temporale (Wernicke’s area)

•

Temporal lobe, posterior lateral fissure

•

Language comprehension Primary auditory cortex (Heschl’s gyrus)

Anatomical Brain Asymmetries

Theories of the Evolution of Cerebral Asymmetry All theories propose that it’s better to have brain areas that have similar functions be in the same hemisphere Analytic-synthetic theory

• Two modes of thinking: analytic (left) and synthetic (right) • Vague and essentially untestable

Motor theory

• Left controls fine movements – speech is just a category of fine movement • Left damage may produce speech

and

motor deficits

Linguistic theory

When Did Cerebral Lateralization Evolve?

• Lateralization of function may have been present at the beginning of vertebrate evolution • Right-handedness may have evolved from a preference for use of the right side of the body for feeding • Left-hemisphere dominance is present in species that existed prior to humans • For example: birds, dogs, monkeys Copyright © Pearson Education 2011

What Are the Survival Advantages of Cerebral Lateralization?

•

Increased neural efficiency to concentrate function in one hemisphere

•

Two cognitive processes may be more readily performed simultaneously if both are lateralized to the same hemisphere

Evolution of Human Language

• • •

Nonhuman primates appear to have more ability in comprehending sounds vs. making vocal calls This fits with the “motor theory of speech perception”: posits that there is overlap between speech comprehension and motor regions involved in speech production Chimpanzees have a highly nuanced vocabulary of hand gestures

•

May indicate a stage in the development of human language

Learning to Read

•

Language localization: place within the hemisphere of language circuitry

•

Wernicke-Geschwind Model: the predominant theory of langauge localization

Historical Antecedents of the Wernicke-Geschwind Model

• •

Broca’s area – speech production

• Damage leads to expressive aphasia • Normal comprehension; speech is meaningful, but awkward

Wernicke’s area – speech comprehension

The Wernicke-Geschwind Model

Wernicke-Geschwind Model: The Evidence

•

Lack of evidence that damage to various parts of the cortex has expected effects

•

Surgery that destroys only Broca’s area has no lasting effects on speech

•

Removal of much of Wernicke’s area has no lasting effects on speech

Effects of Cortical Damage on Language Abilities

• No aphasic patients have damage restricted to Broca’s or Wernicke’s areas • Aphasics almost always have damage to subcortical white matter • Large anterior lesions most likely to produce expressive symptoms • Large posterior lesions most likely to produce receptive symptoms • Global aphasia is usually related to massive lesions of several regions • Aphasics sometimes have damage that does not encroach on Wernicke Geschwind areas Copyright © Pearson Education 2011

Effects of Cortical Damage on Language Abilities

Effects of Electrical Stimulation to the Cortex on Language Abilities

• Stimulated sites that affected language were not necessarily within the boundaries of the Wernicke Geschwind language areas • There were major differences between subjects in the organization of language abilities Copyright © Pearson Education 2011

Effects of Electrical Stimulation to the Cortex on Language Abilities FIGURE 16.14: The responses of the left hemisphere of a 37-year-old epileptic to electrical stimulation. Numbered cards were placed on the brain during surgery to mark the sites where brain stimulation had been applied. (Based on Penfield & Roberts, 1959.)

Effects of Electrical Stimulation to the Cortex on Language Abilities Figure 16.15: The wide distribution of left hemisphere sites where cortical stimulation either blocked speech or disrupted it. (Based on Penfield & Roberts, 1959)

Current Status of the Wernicke-Geschwind Model

• •

Empirical evidence supports two elements

•

Important roles played by Broca’s and Wernicke’s – many aphasics have damage in these areas

•

Anterior damage associated with expressive deficits and posterior with receptive No support for more specific predictions

•

Damage limited to identified areas has little lasting effect on language

• •

Brain damage in other areas can produce aphasia Pure aphasias (expressive OR receptive) rare

Cognitive Neuroscience of Language

•

Premise: activity in brain areas for specific cognitive processes . . .

• • •

underlie language-related behaviors have functions independent of language are likely to be small, widely distributed, and specialized

Functional Brain Imaging and Localization of Language

• •

Bevalier’s fMRI study of reading

cortical involvement in reading – sought to establish Reading sentences versus control periods (strings of consonants) – Areas of activity were tiny and spread out – Active areas varied between subjects and trials – Activity was widespread Copyright © Pearson Education 2011

Damasio’s PET Study of Naming

•

Domasio and colleagues (1996) PET study of naming

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Images of famous faces, animals, and tools

•

Activity while judging image orientation subtracted from activity while naming

•

Left temporal lobe areas activated by naming varied with category

•

Activity seen well beyond Wernicke’s area

Cognitive Neuroscience of Dyslexia

• •

Dyslexia – reading difficulties not due to some other deficit (e.g., vision, intelligence) Developmental dyslexia learning to read – apparent when

•

Heritability estimate = 50%

• •

Acquired dyslexia

•

More common in boys than girls Due to brain damage

•

Relatively rare

Developmental Dyslexia: Causes and Neural Mechanisms

• • •

Brain differences identified, but none seems to play a role in the disorder Multiple types of developmental dyslexia – possibly multiple causes Perhaps a deficit of phonological processing rather than sensorimotor processing

Cognitive Neuroscience of Deep and Surface Dyslexia Two procedures for reading aloud: Lexical (using stored information about words), and Phonetic (sounding out) Surface dyslexia Deep dyslexia Lexical procedure lost, can’t recognize words Phonetic procedure lost, can’t sound out unfamiliar words

Note: To view the MyPsychLab assets, please make sure you are connected to the internet and have a browser opened and logged into www.mypsychlab.com

Watch: Video of the forebrain Watch: Video of the midbrain Watch: Video of the hindbrain Interaction: Animation: Wernicke-Geschwind Model Interaction: Animation: The Functions of the Two Cerebral Hemispheres

Acknowledgments

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Slide template template Ch16 Image

3, 17, 38 4 5, 6 14 15 16 18 10, 22, 28, 35, 49 11 12 13 19 21 23, 41 23, 41 24

Image Description

lightning background texture Hands holding model of brain book Figure 16.1

Figure 16.2

painter colored gender symbols man woman brain Figure 16.3

white rat Figure 16.4

Man's head Figure 16.5

choosing between éclair and apple head - woman Figure 16.6

Figure 16.7

notebook yellow pad person reading books

Image Source

©istockphoto.com/Soubrette ©istockphoto.com/Hedda Gjerpen ©istockphoto.com/Amanda Rohde ©istockphoto.com/Carmen Martínez Banús Pinel 8e, p. 412 Pinel 8e, p. 413 ©istockphoto.com/VikramRaghuvanshi ©istockphoto.com/Andrew Johnson ©istockphoto.com/Stephen Kirklys Pinel 8e, p. 415 ©iStockphoto.com/Elena Butinova Pinel 8e, p. 416 ©istockphoto.com/Nicolas Hansen Pinel 8e, p. 417 ©istockphoto.com/Designs of Integrity ©istockphoto.com/Angel Herrero de Frutos Pinel 8e, p. 419; woman: EDHAR/Shutterstock; man: Jason Stitt/Shutterstock Pinel 8e, p. 421 ©istockphoto.com/stockcam ©istockphoto.com/DNY59 ©iStockphoto.com/Francesco Ridolfi Copyright © Pearson Education 2011

Acknowledgments

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Image Description

Table 16.1

person thinking Figure 16.8

woman observing & taking notes grey parrot golden retriever chimpanzee smiling chimpanzee/laptop toddler listening to adult speak child reading aloud Figure 16.10

Figure 16.11

left profile talking right profile talking Figure 16.13

Figure 16.14

Figure 16.15

colored smoke neuron

Image Source

Pinel 8e, p. 423 ©istockphoto.com/akurtz Pinel 8e, p. 425 ©istockphoto.com/Claudio Arnese ©istockphoto.com/Life on White ©istockphoto.com/Lisa Svara ©istockphoto.com/Eric Isselée ©istockphoto.com/Life on White ©istockphoto.com/Jani Bryson Studios, Inc.

©istockphoto.com/bobbieo Pinel 8e, p. 430 Pinel 8e, p. 431 ©istockphoto.com/Digital Savant LLC ©istockphoto.com/See Hear Media, Inc.

Acknowledgments

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Image Description

Figure 16.16

PET scan messy files laptop table and wall

Image Source

2605_lect16.ppt

Transcript 2605_lect16.ppt

Topics

Major differences between the function of the left and right cerebral hemispheres Cerebral commissures connect the two halves of the brain Split-brain patients have been studied to understand what happens when these connections are severed

Cerebral Lateralization of Function

Tests of Cerebral Lateralization

The Split Brain

Split-Brain Cats

Split-Brain Cats

Commissurotomy in Human Epileptics

Commissurotomy in Human Epileptics

Cross-cuing – facial feedback from the other hemisphere

Doing Two Things at Once

The Chimeric Figures Test

The Lens

The Z Lens

Usually in split-brain patients the left hemisphere is dominant in most everyday activities For some, the right is dominant and this can create conflict between hemispheres

Examples of Cerebral Lateralization of Function

Broad categories are not lateralized – individual tasks may be Better to consider lateralization of

– individual congitive elements

Anatomical Brain Asymmetries

Anatomical Brain Asymmetries

Evolution of Human Language

Learning to Read

The Wernicke-Geschwind Model

The Wernicke-Geschwind Model

Lack of evidence that damage to various parts of the cortex has expected effects

Cognitive Neuroscience of Dyslexia

Brain differences identified, but none seems to play a role in the disorder Multiple types of developmental dyslexia – possibly multiple causes Perhaps a deficit of phonological processing rather than sensorimotor processing

Acknowledgments

Acknowledgments

Acknowledgments

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