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Unformatted text preview: Cognitive Neuroscience Where is language? Where is Language? In the tongue ( as late as the 19C) th In the 4 ventricle (Dark Ages and Renaissance) In the frontal lobes (Gall & phrenologists) rd In the 3 frontal convolution (inferior frontal gyrus) (Broca1861) In the left hemisphere (Broca1865) st In the 1 temporal convolution (superior temporal gyrus) (Wernicke1874) Broca (18241880) 1861 "Tan" (Lebourgne): Good comprehension Could only produce "tan" Selective deficit affecting language production Conclusion: expressive language localized to BA 44,45 Wernicke (18481904) German physician At age 26 (1874) published book on aphasia (The Aphasia Symptom Complex) Described patients with impaired language comprehension and damage to the superior temporal gyrus Language production was also impaired in these patients--not telegraphic fluent and somewhat "empty" Broca's Wernicke's
AL (8 years after his stroke): "Well its a its a its a place and its a girl and a boy ... and they've got obviously something which is is made some made made made well its just beginning to go and be rather unpleasant (ha! ha!) um and this is in the this is the the woman and she's put putting some stuff and the its its that's being really too big to do and nobody seems to have got anything there at all at all and er its ... I'm rather surprised that but there you are this this er this stuff this is coming they were both being one and another er put here and er um um I suppose the idea is that the er two people should be fairly good but I think its going to go somewhere and as I say its down again .. let's see what else has gone er the the this is just I don't know how she di' how they did this but it must have been fairly hard when they did it and er I think there isn't very much there I think." Clinical categories Broca's and Wernicke's aphasia (anterior and posterior aphasias) Both show comprehension and production impairments Overall different patterns of speech and comprehension deficits However, considerable variability among individuals that fall within these general categories The variability indicates that different individuals may have damage to a different subset of the complex set of functions involved in language comprehension and production Language lateralization: Is language exclusively localized to one (left) hemisphere?? Broca only argued for left hemisphere localization of language in 1865 (4 years after his presentation of the case of Tan) He noticed that all his cases had left hemisphere damage Neuroanatomical Asymmetries Neuroanatomical Asymmetries: Planum temporale Heschl's gyrus 1ary auditory Planum temporale st Present from 31 week of gestation Is there ANY right hemisphere language? Techniques: WADA Commissurotomy Hemispherectomy Why should handedness and language lateralization be related? Comissurotomy Initially there appeared to be few consequences Led to jokes about the function of the 200,000,000 fibers of the CC. Its purpose is: to transmit epileptic seizures Prevent the two hemispheres from sagging (Lashley) Testing the hemispheres separately Chimeric figures: Commisurotomy Isolated right hemisphere: No verbal responses In some individuals, limited ability to identify written words In some individuals, limited ability to produce written responses with the left hand Isolated left hemisphere: No spoken or written language impairments Hemispherectomy Surgical treatment for tumors, Rasmussen's syndrome Hemispherectomy Isolated right hemisphere: Children comprehension: very good production: limited Adults comprehension: moderate production: very limited Isolated left hemisphere: Comprehension and production: normal (tone disrupted--"robotic") Right hemisphere language? Evidence from lesion methods At best: Limited, redundant Significant differences between comprehension and production Considerable plasticity in response to early damage Concern: These brains may have been abnormal typically long periods in which reorganization could have taken place Right hemisphere language? Evidence from neuroimaging Bilateral activation is often reported Leftright asymmetry is greatest for: Written vs. auditory input Sentences vs. single words Production vs. comprehension Why the difference between lesion and neuroimaging? Necessary vs. sufficient neural substrates Automatic activation of a formerly active or redundant system with latent language structure Articulation Syntax Phonology, Morphology Lexicon, Semantics Orthography Main Brain areas involved in language (Demonet et. al., 2005) Syntax Local vs Hierarchical Structure The The man asked whether the boy lied The girl read quickly the long story Hierarchical, longdistance dependency between Complementizer whether and Verb lied Local, sequential dependency between Modifier quickly and Verb lied Opitz and Friederici (2007) Are hierarchical and local dependencies processed in different brain areas? Subjects learned an artificial grammar (BROCANTO). Could discriminate between grammatical & ungrammatical sentences (80% corr.) In fMRI, subjects saw grammatical and ungrammatical BROCANTO sentences. Violation in longdistance hierarchical dependency Violation in local dependency Do the different kinds of violations affect different brain areas? The man asked whether the boy aak gum prez rufi lied The girl read quickly the long story aak plox glif rix The girl read lied aak boke the long gum story aak trul rix The man asked quickly the boy lied Ungrammatical Analysis & Results Looked for brain areas that showed increased response to violations and this response correlated with discrimination ability across participants. Found two regions: Left IFG Left vPMC Correct Local Distant Correct Local Distant Analysis & Results Then split subjects into two groups Highproficiency (top half, acc. 86%) Lowproficiency (bottom half, acc. 68%) High Proficiency Low Proficiency High Proficiency Low Proficiency Local Distant Local Distant Local Distant Local Distant Conclusions Hierarchical dependencies Represented in left IFG Learned by the more proficient learners Local dependencies Represented in left vPMC Unaffected by proficiency level Converging hypotheses Fiebach & Schubotz (2006) vPMC: simple sequence processor sequence templates IFG : hierarchical sequence processor (sequences of sequences) Grewe, Bornkessel & colleagues IFG : hierarchical structure linear sequence ...
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This note was uploaded on 07/29/2008 for the course NEUROSCIEN 70 taught by Professor Whitney during the Spring '08 term at Johns Hopkins.
- Spring '08