1. Copyright © 2009 Allyn & Bacon Chapter 16 Lateralization, and the Split Brain

2. Copyright © 2009 Allyn & Bacon 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 – what happens when the connections are severed?

3. Copyright © 2009 Allyn & Bacon The cerebral hemispheres and cerebral commissures

4. Copyright © 2009 Allyn & Bacon Discovery of 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 – difficulty performing movements

5. Copyright © 2009 Allyn & Bacon Cerebral Lateralization of Function (continued) 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

6. Copyright © 2009 Allyn & Bacon Discovery of Speech Laterality, Handedness, and Sex Differences Left hemisphere is speech dominant in almost all dextrals (right-handers) and most sinestrals (left-handers) Females may use both hemispheres more often for language tasks than men do (females may be less lateralized)

7. Copyright © 2009 Allyn & Bacon 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 to contralateral hemisphere

8. Copyright © 2009 Allyn & Bacon The Split Brain (continued) Restricting visual information to one hemisphere in cats

9. Copyright © 2009 Allyn & Bacon 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

10. Copyright © 2009 Allyn & Bacon Myers and Sperry’s (1953) groundbreaking split-brain experiment.

11. Copyright © 2009 Allyn & Bacon 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

12. Copyright © 2009 Allyn & Bacon Commissurotomy in Human Epileptics (continued) The testing procedure that was used to evaluate the neuropsycho- logical status of split-brain patients

13. Copyright © 2009 Allyn & Bacon Split-Brain Patients’ Hemi- spheres Function Separately Left hemisphere can tell what it has seen, right hemisphere can only show it 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

14. Copyright © 2009 Allyn & Bacon Examples of Lateralization of Function Right hemisphere superiority Spatial ability Emotion Musical ability Some memory tasks Left hemisphere – superior in controlling ipsilateral movement

15. Copyright © 2009 Allyn & Bacon Abilities that display cerebral lateralization of function

16. Copyright © 2009 Allyn & Bacon Chapter 16 Lateralization, and the Split Brain

17. Copyright © 2009 Allyn & Bacon 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 – what happens when the connections are severed?

18. Copyright © 2009 Allyn & Bacon The cerebral hemispheres and cerebral commissures

19. Copyright © 2009 Allyn & Bacon Discovery of 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 – difficulty performing movements

20. Copyright © 2009 Allyn & Bacon Cerebral Lateralization of Function (continued) 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

21. Copyright © 2009 Allyn & Bacon Discovery of Speech Laterality, Handedness, and Sex Differences Left hemisphere is speech dominant in almost all dextrals (right-handers) and most sinestrals (left-handers) Females may use both hemispheres more often for language tasks than men do (females may be less lateralized)

22. Copyright © 2009 Allyn & Bacon 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 to contralateral hemisphere

23. Copyright © 2009 Allyn & Bacon The Split Brain (continued) Restricting visual information to one hemisphere in cats

24. Copyright © 2009 Allyn & Bacon 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

25. Copyright © 2009 Allyn & Bacon Myers and Sperry’s (1953) groundbreaking split-brain experiment.

26. Copyright © 2009 Allyn & Bacon 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

27. Copyright © 2009 Allyn & Bacon Commissurotomy in Human Epileptics (continued) The testing procedure that was used to evaluate the neuropsycho- logical status of split-brain patients

28. Copyright © 2009 Allyn & Bacon Split-Brain Patients’ Hemi- spheres Function Separately Left hemisphere can tell what it has seen, right hemisphere can only show it 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

29. Copyright © 2009 Allyn & Bacon Examples of Lateralization of Function Right hemisphere superiority Spatial ability Emotion Musical ability Some memory tasks Left hemisphere – superior in controlling ipsilateral movement

30. Copyright © 2009 Allyn & Bacon Abilities that display cerebral lateralization of function

31. Copyright © 2009 Allyn & Bacon Dyslexia Pathological difficulty in reading Developmental Apparent in children 5.3-11.8% Boys more often than girls Acquired Caused by brain damage Rare

32. Copyright © 2009 Allyn & Bacon Developmental Genetic component (50% heritability) No single kind of brain pathology has been identified  so many kinds; no consistency So many neurological correlates Attentional & sensorimotor deficits caused by damage to magnocellular layers of LGN Phonological Processing