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    Pinel basics ch14 Pinel basics ch14 Presentation Transcript

    • Chapter 14 Lateralization, Language, and the Split Brain The Left Brain and the Right Brain of Language
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    • Lateralization of Function
      • Major differences between the function of the left and right cerebral hemispheres
      • Cerebral commissures connect the 2 halves of the brain
      • Split-brain patients – what happens when the connections are severed?
    •  
    • Cerebral Lateralization of Function
      • 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 – difficulty performing movements when asked to so out of context – also a consequence of damage on the left
    • Cerebral Lateralization of Function
      • 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
    • 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
      • Functional brain imaging
        • f MRI 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
      • Females may use both hemispheres more often for language tasks than men do – less lateralized
    • The Split Brain
      • Corpus callosum – largest cerebral commissure
        • Transfers learned information from one hemisphere to the other
        • When cut, each hemisphere functions independently
      • Studying split-brain cats – transect corpus callosum and optic chiasm so that visual information can’t cross
    • The Split Brain
    • 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
        • Intact cats or those with an intact corpus callosum or optic chiasm – learning transfers between hemispheres
      • Similar findings with split-brain monkeys
    •  
    • Commissurotomy in Human Epileptics
      • Commissurotomy limits convulsive activity
        • many never have another major convulsion
      • Sperry & Gazzaniga
        • developed procedures to test split-brain patients
      • Differ from split-brain animals in that the 2 hemispheres have very different abilities – most left hemispheres are capable of speech, while the right aren’t
    • Testing Split-Brain Patients
    • Hemispheres of Split-Brain Patients Function Independently
      • Left hemisphere can tell what it has seen, right hemisphere can show it.
      • Studies of split-brain patients:
      • 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 they do not know what it was
      • Left hand can show you what it was, right can’t
    • Cross-Cuing
      • Allows the two hemispheres of a split-brain subject to communicate with each other indirectly .
      • Gazzaniga’s color test showed that neurological patients make use of various strategies, including interpreting their own physical cues, to correct their answers.
    • Learning 2 Things at Once
      • Each hemisphere of a split-brain can learn independently and simultaneously
      • Presented with 2 different visual stimuli
      • Helping-hand phenomenon – the hand that “knows” may correct the other
      • Chimeric figures task
    • Dual Mental Functioning and Conflict in Split-Brain Patients
      • In most split-brain patients, the left hemisphere seems to control most activities.
      • In a few patients, the right hemisphere takes a more active role in controlling behavior, which can create conflicts between the left and right hemispheres.
      • Peter, the Split-Brain Patient
    • Differences Between the Hemispheres
      • For many functions the hemispheres do not differ and where there are differences, these tend to be minimal
      • Lateralization of function is statistical, not absolute
      • Right hemisphere has some language abilities
    • Examples of Lateralization of Function
      • Right hemisphere superiority
        • Spatial ability
        • Emotion
        • Musical ability
        • Some memory tasks
      • Left hemisphere – superior in controlling ipsilateral movement
    • Right hemisphere superiority
      • Spatial ability
        • Better at matching 3-D image with 2-D
      • Emotion
        • Better at perceiving facial expressions and mood
      • Musical ability
        • Better at perception of melodies
      • Some memory tasks
        • Nonverbal material
        • Learning tasks where context doesn’t matter
    • 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 cognitive elements
      • Example – left is better at judging above or below, right at how close 2 things are
    • Anatomical Brain Asymmetries
      • Planum temporale (Wernicke’s Area)
        • Temporal lobe, posterior lateral fissure
        • Language comprehension
      • Heschl’s gyrus - primary auditory cortex
      • Frontal operculum (Broca’s Area)
        • Near face area of primary motor cortex
        • Language production
    • Anatomical Brain Asymmetries
    • Anatomical Brain Asymmetries
      • Although asymmetries are seen in language related areas, these regions are not all larger in the left
      • Left planum temporal – larger in 65%
      • Heschl’s gyri – larger on the right
        • 2 in the right, only 1 in left
      • Frontal operculum – visible surface suggests right is larger, but there is greater volume on left
    • Theories of Cerebral Aysmmetry
      • All propose 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”
    • Theories of Cerebral Aysmmetry
      • 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
    • Evolution of Lateralization of Function
      • Nonhuman primates tend to use their right hand for certain tasks
      • Hand preference is under genetic influence in chimps
      • Indicates tool use was not the major factor in the evolution of lateralization
      • Lateralization of aspects of communcation and emotion also seen in other species
    • Antecedents of the Wernicke-Geschwind Model
      • Language localization – intrahemispheric organization of language circuitry
      • Broca’s area – production
        • Damage > expressive aphasia
        • Normal comprehension, speech is meaningful – but awkward
      • Wernicke’s area – comprehension
        • Damage > receptive aphasia
        • Poor comprehension, speech sounds normal – but has no meaning – ‘word salad’
    • Antecedents of the Wernicke-Geschwind Model
      • Arcuate fasciculus – connects Broca’s and Wernicke’s
        • Damage > conduction aphasia
        • Comprehension and speech normal
          • Unable to repeat
      • Left angular gyrus – posterior to Wernicke’s area
        • Damage > alexia (inability to read) and agraphia (inability to write)
    •  
    •  
    • Evaluation of the Wernicke-Geschwind Model
      • Can it predict the deficits produced by damage to various parts of the cortex?
      • Surgery that destroys only Broca’s area has no lasting effects on speech
      • Removal of much of Wernicke’s area does not have any lasting effects on speech
      • Some argue that failure to support the model is due to pathology-related reorganization
    • Effects of Damage to Areas of Cortex on Language Abilities
    • Current Status of the Wernicke-Geschwind Model
      • Empirical evidence supports 2 elements:
        • Important roles played 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 Approach to Language
      • Language-related behaviors are mediated by activity in brain areas involved in the specific cognitive processes required for the behaviors.
      • Brain areas involved in language have other functions.
      • Brain areas involved in language are likely to be small, widely distributed, and specialized.
    • Functional Brain Imaging and Language
      • f MRI and reading – Bavelier determines the extent of cortical involvement in reading
      • Use a sensitive f MRI machine to record activity during reading of sentences
        • Areas of activity were tiny and spread out.
        • Active areas varied between subjects and trials.
        • Activity was widespread.
    • Functional Brain Imaging and Language
    • f MRI and Reading
      • More activity in the left hemisphere than in the right
      • Activity extended well beyond what Wernicke-Geschwind predicted
    • Functional Brain Imaging and Language
      • PET and naming
        • 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 Approach and Dyslexia
      • Dyslexia – reading difficulties not due to some other deficit
      • Developmental dyslexia – apparent when learning to read
      • Acquired dyslexia – due to brain damage
    • Developmental Dyslexia
      • Brain differences identified, but none seems to play a role in the disorder
      • Multiple types of developmental dyslexia – possibly multiple causes
      • Differences could be due to reading problems, not the cause of difficulties
    • Developmental Dyslexia
      • Various subtle visual, auditory, and motor deficits are commonly seen
      • Are these deficits the primary problem – do they cause the dyslexia?
      • Genetic component – yet the disorder is also influenced by culture
      • More English speakers are dyslexic than Italian – due to English being more complex
    • Acquired Dyslexia - Deep and Surface
      • Two procedures for reading aloud
        • Lexical – using stored information about words
        • Phonetic – sounding out
      • Surface dyslexia – lexical procedure lost, can’t recognize words
      • Deep dyslexia – phonetic procedure lost, can’t sound out unfamiliar words
    • Acquired Dyslexia - Deep and Surface
      • Where’s the damage?
      • Deep dyslexia – extensive damage to left-hemisphere language areas
      • How is it that lexical abilities are spared?
        • Lexical abilities may be housed in left language areas that are spared
        • Lexical abilities may be mediated by the right hemisphere
        • Evidence for both exists