Pinel basics ch14


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Pinel basics ch14

  1. 1. Chapter 14 Lateralization, Language, and the Split Brain The Left Brain and the Right Brain of Language <ul><li>This multimedia product and its contents are protected under copyright law. The following are prohibited by law: </li></ul><ul><li>any public performance or display, including transmission of any image over a network; </li></ul><ul><li>preparation of any derivative work, including the extraction, in whole or in part, of any images; </li></ul><ul><li>any rental, lease, or lending of the program. </li></ul>
  2. 2. Lateralization of Function <ul><li>Major differences between the function of the left and right cerebral hemispheres </li></ul><ul><li>Cerebral commissures connect the 2 halves of the brain </li></ul><ul><li>Split-brain patients – what happens when the connections are severed? </li></ul>
  3. 4. Cerebral Lateralization of Function <ul><li>Aphasia – deficit in language comprehension or production due to brain damage – usually on the left </li></ul><ul><li>Broca’s area – left inferior prefrontal cortex – damage leads to expressive aphasia </li></ul><ul><li>Apraxia – difficulty performing movements when asked to so out of context – also a consequence of damage on the left </li></ul>
  4. 5. Cerebral Lateralization of Function <ul><li>Aphasia and apraxia – associated with damage to left hemisphere </li></ul><ul><li>Language and voluntary movement seem to be controlled by one half of the brain – usually the left </li></ul><ul><li>Suggests that one hemisphere is dominant, controlling these functions </li></ul>
  5. 6. Tests of Cerebral Lateralization <ul><li>Determining which hemisphere is dominant </li></ul><ul><li>Sodium amytal test </li></ul><ul><ul><li>Anesthetize one and check for language function </li></ul></ul><ul><li>Dichotic listening </li></ul><ul><ul><li>Report more digits heard by the dominant half </li></ul></ul><ul><li>Functional brain imaging </li></ul><ul><ul><li>f MRI or PET used to see which half is active when doing a language test </li></ul></ul>
  6. 7. Speech Laterality, Handedness, and Sex <ul><li>Dextrals: right-handers </li></ul><ul><li>Sinestrals: left-handers </li></ul><ul><li>Left-hemisphere dominant in almost all dextrals and most sinestrals </li></ul><ul><li>Females may use both hemispheres more often for language tasks than men do – less lateralized </li></ul>
  7. 8. The Split Brain <ul><li>Corpus callosum – largest cerebral commissure </li></ul><ul><ul><li>Transfers learned information from one hemisphere to the other </li></ul></ul><ul><ul><li>When cut, each hemisphere functions independently </li></ul></ul><ul><li>Studying split-brain cats – transect corpus callosum and optic chiasm so that visual information can’t cross </li></ul>
  8. 9. The Split Brain
  9. 10. Split-Brain Cats <ul><li>Each hemisphere can learn independently </li></ul><ul><li>Split-brain cats with one eye patched </li></ul><ul><ul><li>Learn task as well as controls </li></ul></ul><ul><ul><li>No memory or savings demonstrated when the patch was transferred </li></ul></ul><ul><ul><li>Intact cats or those with an intact corpus callosum or optic chiasm – learning transfers between hemispheres </li></ul></ul><ul><li>Similar findings with split-brain monkeys </li></ul>
  10. 12. Commissurotomy in Human Epileptics <ul><li>Commissurotomy limits convulsive activity </li></ul><ul><ul><li>many never have another major convulsion </li></ul></ul><ul><li>Sperry & Gazzaniga </li></ul><ul><ul><li>developed procedures to test split-brain patients </li></ul></ul><ul><li>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 </li></ul>
  11. 13. Testing Split-Brain Patients
  12. 14. Hemispheres of Split-Brain Patients Function Independently <ul><li>Left hemisphere can tell what it has seen, right hemisphere can show it. </li></ul><ul><li>Studies of split-brain patients: </li></ul><ul><li>Present a picture to the right visual field (left brain) </li></ul><ul><li>Left hemisphere can tell you what it was </li></ul><ul><li>Right hand can show you, left hand can’t </li></ul><ul><li>Present a picture to the left visual field (right brain) </li></ul><ul><li>Subject will report that they do not know what it was </li></ul><ul><li>Left hand can show you what it was, right can’t </li></ul>
  13. 15. Cross-Cuing <ul><li>Allows the two hemispheres of a split-brain subject to communicate with each other indirectly . </li></ul><ul><li>Gazzaniga’s color test showed that neurological patients make use of various strategies, including interpreting their own physical cues, to correct their answers. </li></ul>
  14. 16. Learning 2 Things at Once <ul><li>Each hemisphere of a split-brain can learn independently and simultaneously </li></ul><ul><li>Presented with 2 different visual stimuli </li></ul><ul><li>Helping-hand phenomenon – the hand that “knows” may correct the other </li></ul><ul><li>Chimeric figures task </li></ul>
  15. 17. Dual Mental Functioning and Conflict in Split-Brain Patients <ul><li>In most split-brain patients, the left hemisphere seems to control most activities. </li></ul><ul><li>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. </li></ul><ul><li>Peter, the Split-Brain Patient </li></ul>
  16. 18. Differences Between the Hemispheres <ul><li>For many functions the hemispheres do not differ and where there are differences, these tend to be minimal </li></ul><ul><li>Lateralization of function is statistical, not absolute </li></ul><ul><li>Right hemisphere has some language abilities </li></ul>
  17. 19. Examples of Lateralization of Function <ul><li>Right hemisphere superiority </li></ul><ul><ul><li>Spatial ability </li></ul></ul><ul><ul><li>Emotion </li></ul></ul><ul><ul><li>Musical ability </li></ul></ul><ul><ul><li>Some memory tasks </li></ul></ul><ul><li>Left hemisphere – superior in controlling ipsilateral movement </li></ul>
  18. 20. Right hemisphere superiority <ul><li>Spatial ability </li></ul><ul><ul><li>Better at matching 3-D image with 2-D </li></ul></ul><ul><li>Emotion </li></ul><ul><ul><li>Better at perceiving facial expressions and mood </li></ul></ul><ul><li>Musical ability </li></ul><ul><ul><li>Better at perception of melodies </li></ul></ul><ul><li>Some memory tasks </li></ul><ul><ul><li>Nonverbal material </li></ul></ul><ul><ul><li>Learning tasks where context doesn’t matter </li></ul></ul>
  19. 21. What is Lateralized – Broad Clusters of Abilities or Individual Cognitive Processes? <ul><li>Broad categories are not lateralized – individual tasks may be </li></ul><ul><li>Better to consider lateralization of constituent cognitive processes – individual cognitive elements </li></ul><ul><li>Example – left is better at judging above or below, right at how close 2 things are </li></ul>
  20. 22. Anatomical Brain Asymmetries <ul><li>Planum temporale (Wernicke’s Area) </li></ul><ul><ul><li>Temporal lobe, posterior lateral fissure </li></ul></ul><ul><ul><li>Language comprehension </li></ul></ul><ul><li>Heschl’s gyrus - primary auditory cortex </li></ul><ul><li>Frontal operculum (Broca’s Area) </li></ul><ul><ul><li>Near face area of primary motor cortex </li></ul></ul><ul><ul><li>Language production </li></ul></ul>
  21. 23. Anatomical Brain Asymmetries
  22. 24. Anatomical Brain Asymmetries <ul><li>Although asymmetries are seen in language related areas, these regions are not all larger in the left </li></ul><ul><li>Left planum temporal – larger in 65% </li></ul><ul><li>Heschl’s gyri – larger on the right </li></ul><ul><ul><li>2 in the right, only 1 in left </li></ul></ul><ul><li>Frontal operculum – visible surface suggests right is larger, but there is greater volume on left </li></ul>
  23. 25. Theories of Cerebral Aysmmetry <ul><li>All propose that it’s better to have brain areas that do similar things be in the same hemisphere </li></ul><ul><li>Analytic-synthetic theory </li></ul><ul><ul><li>2 modes of thinking, analytic (left) and synthetic (right) </li></ul></ul><ul><ul><li>Vague and essentially untestable </li></ul></ul><ul><ul><li>“ the darling of pop psychology” </li></ul></ul>
  24. 26. Theories of Cerebral Aysmmetry <ul><li>Motor theory </li></ul><ul><ul><li>Left controls fine movements – speech is just a category of movement </li></ul></ul><ul><ul><li>Left damage may produce speech and motor deficits </li></ul></ul><ul><li>Linguistic theory </li></ul><ul><ul><li>Primary role of left is language </li></ul></ul>
  25. 27. Evolution of Lateralization of Function <ul><li>Nonhuman primates tend to use their right hand for certain tasks </li></ul><ul><li>Hand preference is under genetic influence in chimps </li></ul><ul><li>Indicates tool use was not the major factor in the evolution of lateralization </li></ul><ul><li>Lateralization of aspects of communcation and emotion also seen in other species </li></ul>
  26. 28. Antecedents of the Wernicke-Geschwind Model <ul><li>Language localization – intrahemispheric organization of language circuitry </li></ul><ul><li>Broca’s area – production </li></ul><ul><ul><li>Damage > expressive aphasia </li></ul></ul><ul><ul><li>Normal comprehension, speech is meaningful – but awkward </li></ul></ul><ul><li>Wernicke’s area – comprehension </li></ul><ul><ul><li>Damage > receptive aphasia </li></ul></ul><ul><ul><li>Poor comprehension, speech sounds normal – but has no meaning – ‘word salad’ </li></ul></ul>
  27. 29. Antecedents of the Wernicke-Geschwind Model <ul><li>Arcuate fasciculus – connects Broca’s and Wernicke’s </li></ul><ul><ul><li>Damage > conduction aphasia </li></ul></ul><ul><ul><li>Comprehension and speech normal </li></ul></ul><ul><ul><ul><li>Unable to repeat </li></ul></ul></ul><ul><li>Left angular gyrus – posterior to Wernicke’s area </li></ul><ul><ul><li>Damage > alexia (inability to read) and agraphia (inability to write) </li></ul></ul>
  28. 32. Evaluation of the Wernicke-Geschwind Model <ul><li>Can it predict the deficits produced by damage to various parts of the cortex? </li></ul><ul><li>Surgery that destroys only Broca’s area has no lasting effects on speech </li></ul><ul><li>Removal of much of Wernicke’s area does not have any lasting effects on speech </li></ul><ul><li>Some argue that failure to support the model is due to pathology-related reorganization </li></ul>
  29. 33. Effects of Damage to Areas of Cortex on Language Abilities
  30. 34. Current Status of the Wernicke-Geschwind Model <ul><li>Empirical evidence supports 2 elements: </li></ul><ul><ul><li>Important roles played Broca’s and Wernicke’s – many aphasics have damage in these areas </li></ul></ul><ul><ul><li>Anterior damage associated with expressive deficits and posterior with receptive </li></ul></ul><ul><li>No support for more specific predictions </li></ul><ul><ul><li>Damage limited to identified areas has little lasting effect on language </li></ul></ul><ul><ul><li>Brain damage in other areas can produce aphasia </li></ul></ul><ul><ul><li>Pure aphasias (expressive OR receptive) rare </li></ul></ul>
  31. 35. Cognitive Neuroscience Approach to Language <ul><li>Language-related behaviors are mediated by activity in brain areas involved in the specific cognitive processes required for the behaviors. </li></ul><ul><li>Brain areas involved in language have other functions. </li></ul><ul><li>Brain areas involved in language are likely to be small, widely distributed, and specialized. </li></ul>
  32. 36. Functional Brain Imaging and Language <ul><li>f MRI and reading – Bavelier determines the extent of cortical involvement in reading </li></ul><ul><li>Use a sensitive f MRI machine to record activity during reading of sentences </li></ul><ul><ul><li>Areas of activity were tiny and spread out. </li></ul></ul><ul><ul><li>Active areas varied between subjects and trials. </li></ul></ul><ul><ul><li>Activity was widespread. </li></ul></ul>
  33. 37. Functional Brain Imaging and Language
  34. 38. f MRI and Reading <ul><li>More activity in the left hemisphere than in the right </li></ul><ul><li>Activity extended well beyond what Wernicke-Geschwind predicted </li></ul>
  35. 39. Functional Brain Imaging and Language <ul><li>PET and naming </li></ul><ul><ul><li>Images of famous faces, animals, and tools </li></ul></ul><ul><ul><li>Activity while judging image orientation subtracted from activity while naming – </li></ul></ul><ul><li>Left temporal lobe areas activated by naming varied with category </li></ul><ul><li>Activity seen well beyond Wernicke’s Area </li></ul>
  36. 40. Cognitive Neuroscience Approach and Dyslexia <ul><li>Dyslexia – reading difficulties not due to some other deficit </li></ul><ul><li>Developmental dyslexia – apparent when learning to read </li></ul><ul><li>Acquired dyslexia – due to brain damage </li></ul>
  37. 41. Developmental Dyslexia <ul><li>Brain differences identified, but none seems to play a role in the disorder </li></ul><ul><li>Multiple types of developmental dyslexia – possibly multiple causes </li></ul><ul><li>Differences could be due to reading problems, not the cause of difficulties </li></ul>
  38. 42. Developmental Dyslexia <ul><li>Various subtle visual, auditory, and motor deficits are commonly seen </li></ul><ul><li>Are these deficits the primary problem – do they cause the dyslexia? </li></ul><ul><li>Genetic component – yet the disorder is also influenced by culture </li></ul><ul><li>More English speakers are dyslexic than Italian – due to English being more complex </li></ul>
  39. 43. Acquired Dyslexia - Deep and Surface <ul><li>Two procedures for reading aloud </li></ul><ul><ul><li>Lexical – using stored information about words </li></ul></ul><ul><ul><li>Phonetic – sounding out </li></ul></ul><ul><li>Surface dyslexia – lexical procedure lost, can’t recognize words </li></ul><ul><li>Deep dyslexia – phonetic procedure lost, can’t sound out unfamiliar words </li></ul>
  40. 44. Acquired Dyslexia - Deep and Surface <ul><li>Where’s the damage? </li></ul><ul><li>Deep dyslexia – extensive damage to left-hemisphere language areas </li></ul><ul><li>How is it that lexical abilities are spared? </li></ul><ul><ul><li>Lexical abilities may be housed in left language areas that are spared </li></ul></ul><ul><ul><li>Lexical abilities may be mediated by the right hemisphere </li></ul></ul><ul><ul><li>Evidence for both exists </li></ul></ul>