Lateralization of Language ch.16 (cont’d) and Biopsychology of Memory ch. 11

1. Lateralization of Languagech.16 (cont’d)andBiopsychology of Memorych. 11

2. Lateralizationand Cortical Localization of Language Ch. 16 (cont’d)

3. Outline • Differences Between the Left and Right Hemispheres • Broca’s Area • Wernicke’s Area

4. Differences BetweenThe Left and Right Hemispheres • Language is the most lateralized of all abilities; the left-hemisphere is better than the right at most language-related tasks • however, the right hemisphere proved to be able to understand single written and spoken words (video); also right-hemisphere detects prosody and discourse

5. Differences BetweenThe Left and Right Hemispheres • The right hemisphere proved better than the left at a variety of tasks involving spatial ability, emotional stimuli and musical tasks • LH hippocampus is associated with verbal memory and RH hippocampus is associated with spatial memory

6. Differences BetweenThe Left and Right Hemispheres • The two hemispheres seem to engage different types of memory processing; LH attempts to place its experience in a larger context (relation of parts that make up the whole), while the RH attends strictly to the Gestalt perceptual characteristics of the stimulus (either the parts or whole but not relation between) • This is usually termed analytical (LH) versus holistic (RH)

7. Differences BetweenThe Left and Right Hemispheres • Thus the RH should not be regarded as the minor hemisphere; it has different abilities, not less important ones

8. Differences BetweenThe Left and Right Hemispheres • There are also anatomical asymmetries in the human brain; for example the planum temporale and frontal operculum (language related areas) are larger in LH • However, Heschl’s gyrus (also language related) in larger in RH

9. Differences BetweenThe Left and Right Hemispheres • (not in book) left-handers seem to have symmetrical planum temporales, suffer less severely from LH aphasia, and suffer more severely from RH aphasia • This suggests left-handers may have a more diffuse representation of language and is evident in differential strategies in sentence processing

10. Differences BetweenThe Left and Right Hemispheres • For example in priming studies, when the target word is LILY, right-handers are quicker at deciding that it as a word if they are primed with the word ROSE, where as left-handers are quicker at deciding if primed with the word POND

11. Differences BetweenThe Left and Right Hemispheres • LILY and ROSE fit same syntactic templates • i.e., The ___ bloomed. The ___ is a flower. • LILY and POND are associated in real world semantic representation

12. Three Theories ofCerebral Asymmetry • Analytic-synthetic theory • Motor theory • Linguistic theory

13. Analytic-Synthetic Theory • Suggests that there are two fundamentally different modes of thinking, an analytic mode (LH) and synthetic mode (RH), and that the neural circuitry for each is fundamentally different • LH (pieces of the whole) operates in logical, sequential, analytic fashion • RH (the whole) makes immediate, overall synthetic judgments

14. Analytic-Synthetic Theory • Experienced musicians are left-hemisphere dominant for processing music

15. Motor Theory • Posits that LH is specialized for fine motor movement of which speech is but one example • Two lines of evidence: • Lesions of the LH disrupt facial movements more than do RH lesions, even when they are not related to speech • Degree of disruption of nonverbal facial movements is positively correlated with the degree of aphasia

16. Linguistic Theory • Based on the view that the primary function of the LH is language; this is based on studies of deaf people who communicate using ASL; this ability is lost if these people suffer damage to the LH, even when they are able to make the movements required • (or is this just showing ASL is a language, or that language is highly analytical or that ASL requires fine motor movements of the hand like speech does of the mouth/tongue?)

17. Broca’s Area • Inferior left prefrontal area in left hemisphere • Damage leads to deficits primarily in speech production (problems with expression) and also grammatical comprehension

18. Wernicke’s Area • Left posterior temporal area, just posterior to the primary auditory cortex • Damage leads to deficits to semantic language comprehension (problems with reception) and speech is semantically incomprehensible, despite having correct grammar, rhythm and intonation (word salad)

19. Broca’s area (Broadmann’s area 44 and 45) • Wernicke’s area (narrowly defined as BA22 but can also describe BA37, 39 and 40).

20. Conduction Aphasia • Damage to white matter (heavily myelinated) tract connecting Broca’s and Wernicke’s areas called the arcuate fasciculus • Comprehension and spontaneous speech are intact but patient not able to repeat words they have just heard

21. Arcuate fasciculus

22. Arcuate fasciculus

23. Conduction Aphasia • However, conduction aphasics (temporoparietal lesions) are a heterogeneous group in terms of impairment (some more Broca’s aphasic - like, some Wernicke’s aphasic - like) suggesting arcuate fasciculus may not be the only underlying structure

24. Perisylvian language networks of the human brain (Catani, et al., 2005) • Newly discovered but evolutionarily older structure in addition to the classical arcuate fasciculus • parallel and lateral to classical arcuate fasciculus • Connects “Geschwind’s territory” (inferior parietal cortex that receives multimodal inputs important for semantics; BA39 and 40) to classical language areas (Broca’s and Wernicke’s areas) • Rudimentary form of this network exists in the brain of other primates (macaque monkey)

25. Perisylvian language networks of the human brain (Catani, et al., 2005) Arcuate fasciculus (unique to humans; long segment; medial) and other network(anterior segmentand posterior segment)

26. Perisylvian language networks of the human brain (Catani, et al., 2005) • Corroborates neuropsychological evidence for different types of conduction aphasics • Classical conduction aphasia (long segment lesion; failure in automatic repetition) • Transcortical aphasia (anterior segmentlesion; failure to vocalize semantic content) • Sensory aphasia (posterior segment lesion; failure of auditory semantic comprehension)

28. Broca’s area (Broadmann’s area 44 and 45) • Wernicke’s area (narrowly defined as BA22 but can also describe BA37, 39 and 40).

29. Alexia • Damage to the left angular gyrus (area of left temporal and parietal cortex just posterior to Wernicke’s; BA39) • Inability to read despite intact language comprehension and production

30. Agraphia • Also due to damage to the left angular gyrus • Inability to write despite intact language comprehension and production • Involvement of LAG in alexia and agraphia show its responsible for language related visual input

31. Broca’s Aphasic Video(shown in class)

32. Wernicke-Geshwind Model • Seven components in Left hemisphere: primary visual cortex, angular gyrus, primary auditory cortex, Wernicke’s area, arucate fasciculus, Broca’s area, and primary motor cortex

34. Responding to a heard question • Primary auditory cortex to Wernicke’s area where comprehended • To respond, concept generated in Wernicke’s area, goes via arcuate fasciculus to Broca’s area, then to primary motor cortex and articulatory areas (face, lip, and tongue muscles, voice box, and muscles assoicated with lungs) • (animation in class)

35. Reading aloud • Primary visual cortex to left angular gyrus, which transmits visual code to auditory code • Then to Wernicke’s area to arcuate fasciculus to Broca’s to primary motor cortex to articulatory areas • (animation in class)

36. Evidence against W-G Model • Damage to these boundaries has little lasting effect on language • Damage to other brain areas can produce aphasia • Broca’s and Wernicke’s aphasia are rarely “pure” - aphasia is both receptive and expressive • Major individual differences for cortical localization for language

37. Cognitive Neuroscience Approach to Language • Cannot perform lesion studies because humans are only known species with language • Use Cognitive Neuroscience (brain imaging like PET and fMRI) to study relation of brain and language

38. Cognitive Neuroscience Approach to Language • Each of of the components in W-G model can be broken down further into constituent cognitive processes • Phonological analysis (sounds) • Grammatical analysis (structure) • Semantic analysis (meaning)

39. Cognitive Neuroscience Approach to Language (2) Areas of brain involved in language are not solely dedicated to language; many of the constituent cognitive processes also play roles in other behavior Example - some areas involved in short-term memory and visual pattern recognition are involved in reading, too

40. Cognitive Neuroscience Approach to Language (3) W-G model assumes that brain areas involved in language are large, circumscribed, and homogenous but Cognitive Neuroscience assumes they are small, widely distributed, and specialized

41. Dyslexia and Cognitive Neuroscience • Dyslexia is pathological difficulty in reading, does not result from general visual, motor, or intellectual deficits • Developmental dyslexia- apparent in childhood • Acquired dyslexia - damage in individuals who were already capable of reading

42. Developmental Dyslexia (1) Differences between brains of dyslexic and non-dyslexic readers have been reported, however none seems to play a critical role Example - dyslexics do not display the asymmetry of the planum temporale

43. Developmental Dyslexia (2) Several types of dylexias and thus likely to have different causes and brain areas susceptible

44. Developmental Dyslexia (3) Difficult to determine cause-and-effect of brain abnormalities Are these abnormalities the cause of dylexia or the result of lack of reading experience (brain develops differently as a result of different experience)?

45. Acquired Dyslexia • Two strategies for reading aloud: • Lexical procedure - based on specific stored information that has been acquired about written words - looks at it, recognizes it and says it (yacht, aisle) • Phonetic procedure - looks at words, recognizes letters, sounds them out and says word (fish, river, glass)

46. Acquired Dyslexia • Surface Dyslexia - patients lose ability to to pronounce words based on the specific memories of the words (they lose their lexical procedure) • Can pronounce non-words - wug Example: can pronoun words consistent with rules ( fish, river, or glass) but can’t pronounce unusual words (have, lose, and steak are like cave, hose, and beak)

47. Acquired Dyslexia • Deep Dyslexia - patients lose ability to apply common rules of pronunciation ( they lose their phonetic procedure) • Can’t pronounce non-words Example: can say phonetically unusual words like aisle and yacht but cannot pronounce rule-consistent words like fish, river, or glass

48. Acquired Dyslexia • Where are lexical and phonetic processes in the brain? • Deep dyslexia (lose phonetic procedure) due to damage in LH • Surface dyslexia (lose lexical) due to partial LH damage or RH damage

49. The Neuropsychologyof Memory Ch. 11

50. Outline • Review of memory terms • Amnesic Effects of Bilateral Medial Temporal Lobectomy • The case of H.M.