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Lecture 14

PSYO 2470 Lecture 14: language II

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PSYO 2470
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Language II Language and the Brain - When relying on using people with brain damage as study subject, relying on difficulty pinpointing areas o Usually damage spreads beyond one single specific brain area - People with aphasias – very few have trouble using muscles for eating, but have trouble with speech o Trouble in brain to produce words rather than muscular problem o Aphasias – language impairment - Wada procedure o Procedure takes advantage of the two separate hemispheres of the brain o GABAergic drug injected – inhibitory (GABA agonist) ▪ Injected into corroded artery – get reduced firing in one whole hemisphere of the brain • Inhibitory tone in one side of the hemisphere – see how it effects speech ▪ Used to look at roles of hemispheres in language ▪ If inactivate left hemisphere temporarily, people show an inability to speak ▪ • Looked at handedness as well as which hemisphere speech is represented in o Majority of people who are right handed are left hemisphere dominant in speech ▪ Majority of left handed people also had left speech representation in hemisphere • But lower percentage than right handed people – also greater percentage had right hemisphere representation for speech • Majority of people have left hemisphere dominance for speech • Much less of an effect on right hemisphere o Most people are left hemisphere dominant when it comes to language ▪ Some people, though few, had right dominance – more left handed people saw right dominance than right handed people - Laterality with fMRI o Left hemisphere dominance in tasks involving selecting synonyms of words ▪ More activity produced in left hemisphere during task o Activation seen in posterior temporal lobe, medial temporal lobe, and visual cortex o Also activation in auditory cortex o Recruitment of left hemisphere centres of language functions - Language specific areas o o Broca’s area ▪ Larger in left frontal lobe than right frontal lobe ▪ Close to motor areas ▪ Lesions in this area impair articulate speech • Impairs ability to get speech out fluidly – difficulty using vocal apparatus of the mouth and throat to speak • Broca’s area aphasia associated with difficulty in speech production ▪ Important for speech production o Wernicke’s areas ▪ Important for understanding of speech ▪ Superior surface of temporal lobe • Between primary auditory cortex and angular gyrus ▪ Lesion – disrupts speech comprehension • Not difficulty in mechanics of speech, but difficulties with comprehension o Difficulty understanding spoken instructions and will also say things that don’t make sense ▪ Is larger on the left hand side than right hand side of brain o Broca’s aphasia ▪ Problem with moving muscles of the mouth • Effects global apparatus of speech o No problems with other functions of the mouth (i.e. eating) ▪ Depending on age that results in aphasia, can show some improvement after damage • Compensation from different areas or hemispheres of the brain – plasticity o Wernicke’s aphasia ▪ Problems with speech comprehension • Can produce speech – is often nonsensical and can have difficulty understanding verbal instructions Types of aphasia - o Broca’s ▪ Damage to motor association cortex of frontal lobe, or posterior temporal lobe ▪ Good understanding/comprehension of speech ▪ Produced speech is impaired ▪ Have a problem with repletion • Also problems with paraphasic errors – substitute incorrect words or sounds o Wernickes ▪ Daamage to posterior temporal lobe ▪ Comprehension is poor • But produce fluent, grammatical speech that is meaningless o Speech – inserting wrong words, not flowing properly ▪ Have impaired repetition and paraphasic errors o Anomic aphasia ▪ Inability to find words ▪ Affected error – inferior temporal lobe ▪ Can be fluent and grammatical, but still trouble finding words they need - Specific impairment with damage to specific areas o Suggests specific circuits that have specific functions in language Wernicke-Geschwind model - Trying to find unified circuit in language - - Arcuate fasciculus – black arrows in figure o Connects Broca’s and Wernickes via the angular gyrus - Important for production of normal speech patterns and comprehension - How language is communicated – weather oral or written – is important for which system is involved o Auditory language ▪ When repeating a spoke word – activity in auditory cortex • Activity in the loop o All areas involved o Visual ▪ Repeating a written word – primary visual cortex sends projects to angular gyrus • Processing in Broca’s and Wernickes • Activation of primary visual cortex o Activation of Arcuate fasciclus fibre tract loop - Language comprehension and production areas work together o Arcuate fasciculus – fibre tract that connects Broca’s are and Wernicke’s area - When repeating a written word, also see activation in occipital lobe and communication between occipital and language areas o Activation at primary visual cortex ▪ Language comes in and goes through Broca’s area loop - Model is oversimplified Parallel language pathways - - Analogous to previously seen dorsal and ventral streams - Two dorsal pathways (green and blue) o Blue ▪ Involved in speech production and repeating words • Simple language tasks – not a lot of semantic processing – don’t need to know meaning ▪ Activation in Wernicke’s area but bypasses Broca’s area • Involves Wernicke’s area synapsing with premotor cortex o Green ▪ Preferentially active when people have to analyze words according to grammar system • H
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