0317_brain_imagi

0317_brain_imagi - Brain imaging and sentence comprehension...

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Brain imaging and sentence comprehension Ted Gibson March 17, 2005 9.59 / 24.905
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To do today: 1. Deficit-lesion analyses 2. Brain imaging methods: 1. PET 2. fMRI 3. Event-related potentials (ERPs) 4. Magneto-encephalography (MEG) 3. ERPs in detail
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Language and the brain: Evidence from brain damage: Aphasia Broca's aphasia a. spontaneous production difficulty: labored speech, missing function words “son ... university ... smart ... boy ... good ... good”
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Broca's aphasia b. difficulty understanding more complex syntactic relations: object-extracted relative clauses (RCs): poor performance on picture matching or question-answering “The lion that the tiger chased watched the leopard.” Did the tiger chase the lion? subject-extracted RCs: good performance “The lion that chased the tiger watched the leopard.” Did the tiger chase the lion?
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Wernicke's aphasia Language comprehension difficulty: patients cannot understand spoken or written language, but speak fluently, often nonsensically. “I called my mother on the television and did not understand the door. It was not too breakfast, but they came from far to near. My mother is too old for me to be young.'' These and other aphasias are diagnosed behaviorally : based on symptoms of speech production and comprehension.
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Broca's aphasics often have deficits in Broca's area: Left-lateralized, pre-frontal cortex Brain diagram removed for copyright reasons.
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Wernicke's aphasics often have deficits in Wernicke's area: Left-lateralized Brain diagram removed for copyright reasons.
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Imperfect correlation between deficits and lesion sites The Wernicke-Geschwind model / hypothesis : Lexicon (word-meaning relations) is stored / accessed in Wernicke’s area. Broca’s area guides word production. But: Some Broca's aphasics have no deficit in Broca's area. Some Wernicke's aphasics have no deficits in Wernicke's area. Some patients with damage to Broca’s area don’t have Broca’s aphasia. Some patients with damage to Wernicke’s area don’t have Wernicke’s aphasia. We are a long way yet from a functional neuroanatomy of language. Issues: (1) People’s brains are different: (slightly?) functional architectures. (2) All deficits are different.
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Language and the Brain: Language is left-lateralized From the reading (Bear et al. text): • The Wada procedure (developed by John Wada): A fast-acting barbituate is injected into the carotid artery on one side of the neck. The drug is preferentially carried to the ipsolateral hemisphere, acting as an anesthetic for ~10 minutes. 96% of right-handed people have left hemisphere control of speech 70% of left-handed people have left hemisphere control of speech 93% overall have left hemisphere control of speech • Language processing in split-brain patients Surgeons severed the corpus callosum in patients suffering from severe epilepsy Visual stimuli presented in the right visual field cannot be named by these patients. “I see nothing.”
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Neuroimaging and language • Techniques Positron Emission Tomography (PET) Functional Magnetic Resonance Imaging (fMRI) Event-Related Potentials (ERP) Magnetoencephelography (MEG)
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Comparison of Techniques Graph removed for copyright reasons.
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