Language and the Brain Chapter 20 PDF

Language and the Brain Chapter 20   Discuss the definitions of language of speech  Learn about areas of the brain localized for langauge Learning processing objectives  Understand the experimental evidence for how the brain processes language and...

Language and the Brain Chapter 20   Discuss the definitions of language of speech  Learn about areas of the brain localized for langauge Learning processing objectives  Understand the experimental evidence for how the brain processes language and what happens when things go wrong   Language  System by which sounds, symbols, and gestures are used for communication  Process  Language comes into brain through visual and auditory systems.  Motor system: produces speech, writing  Brain processing between sensory and motor systems; essence of language What exactly is language?   Language  A system for representing and communicating information  Uses words combined according to grammatical rules  Expressed in a variety of ways including gestures, writing, and speech  Speech  An audible form of communication built on the sounds humans produce Language vs. speech   Involves coordination of over 100 muscles from those controlling lungs to those of larynx and mouth  All muscles controlled by motor cortex  Air exhaled passes through larynx.  Within larynx are vocal folds.  Sounds produced by vibrations in tightened vocal folds Human  Sounds modified at further stages of vocal tract sound &  Phonemes: fundamental sounds of a language speech production   Human language  Complex, flexible, powerful system for communication  Creative use of words according to rules  Animals do vocalize and use gestures.  Controversial whether their communication is “language”  Do not meet definition of human language: complex, flexible, rules Language in animals   Mechanisms in infants  Recognize word sounds very early  Statistical learning—combinations of sounds  Syllable emphasis  “Motherese”  Adults talk to infants—speech slower, exaggerated, vowel sounds clearly articulated Language  Brain mechanisms for language acquisition poorly understood  Dehaene-Lambertz: fMRI of 3-month-old infant’s brain response to acquisition spoken words similar to adults’   Speech and language disorders run in families, more likely to co- occur in identical twins.  Study of KE family generations with verbal dyspraxia  FOXP2 gene single mutation  Affects development of motor cortex, cerebellum, and striatum  Deficits in muscular control of lower face Genes  FOXP2 strongly expressed in brain areas involved in song learning in involved in birds language   FOXP2, CNTNAP2, and KIAA0319 mutations  Specific language impairment (SLI)  Developmental delay in mastery of language  Not associated with hearing difficulty or more general developmental delays Genetic  Important roles in brain development factors in  Dyslexia: appears to have strong genetic link specific language impairment & dyslexia   Aphasia  Partial/complete loss of language abilities following brain damage  Greek/Roman Empires: tongue thought to control speech  Sixteenth century: speech impairment, tongue not affected Discovery of  1770: Gesner: brain damage  1825: Bouillaud: frontal lobes specialized  1861: Aubertin: cortical area in frontal lobe language areas in the brain   Broca’s area (1864): region of dominant left frontal lobe, articulate speech / production Broca’s are & of speech Wernicke’s  Wernicke’s area (1874): superior surface of temporal lobe between area auditory cortex and angular gyrus, lesions disrupt normal speech & understanding of speech How do we  Wada procedure know which  Used to determine hemisphere dominant for speech side of the  Half the brain is anesthetized while the patient is tested for brain these speech & language skills, then repeat for other half of brain language  Used on neurosurgery areas are in? candidates   Damage in motor association cortex of frontal lobe  Speech is nonfluent, agrammatical.  Difficulty speaking but can understand heard/read language  Paraphasic errors  Pauses to search for words (anomia), Broca’s repeats “overlearned” things, difficulty repeating words aphasia   Posterior temporal lobe damage  Fluent speech but poor comprehension (word salad)  Gardner’s case study  Strange mixture of clarity and gibberish  Correct sounds, incorrect sequence  Speech patterns mirrored in playing music, Wernicke’s writing  Area specialized for storing memories of aphasia sounds that make up words Wernicke-  Proposed pathway for talking: Geshwind  Auditory cortex  model of   Wernicke’s area  Arcuate fasciculus  language  Broca’s area  processing in Motor cortex  the brain   Proposed pathway for reading aloud:  Primary visual cortex  Wernicke-  Angular gyrus   Wernicke’s area  Geshwind  Arcuate fasciculus  model of   Broca’s area  Motor cortex language  Problems with Wernicke- processing in Geshwins model:  A bit too oversimplified the brain  Many patients’ symptoms just don’t make sense if this model is true   “Newer” language processing models, usually preferred over Parallel the Wernicke-Geshwind model language  Similar to dorsal & ventral streams of visual processing processing  Blue: speech production pathways  Green: syntax structure  Red: word meaning   Disconnection lesion of arcuate fasciculus and parietal cortex  In contrast to Broca’s aphasia and Wernicke’s aphasia: comprehension good, speech fluent  Chief deficit: difficulty repeating words  Symptoms: repetition substitutes/omits words, paraphasic errors, cannot repeat function or nonsense words, polysyllabic words Conduction aphasia   Aphasia in bilinguals: Language affected depends on order or learning, fluency, recent use of language.  Sign language aphasias analogous to speech aphasias  but can be produced by lesions in slightly different locations.  Verbal and sign language recovered together in one case  indicating overlapping regions used for both. Aphasia in  Evidence suggests some universality to language processing in the brain. bilingual & deaf persons Asymmetrical  Split-brain studies language  Roger Sperry (1950s)  Split-brain procedure processing in  Sever axons of corpus callosum (lobotomy) the cerebral  Few behavioral effects  Animals behaved as if they had two hemispheres brains.   Michael Gazzaniga: Brief stimuli delivered only to one hemisphere.  Observations: The two hemispheres initiated conflicting eye movement behaviors, suggesting that indeed only one hemisphere is “seeing” the object Split brains in humans   Right visual field, left hemisphere language dominance Left  Left visual field, difficulty verbalizing by right hemisphere in split brain hemisphere  Image only in left visual field, object in left language hand, unable to describe dominance  Unable to describe anything to left of visual fixation point  Doesn’t seem to bother patients!   Functions of right hemisphere: can read and understand numbers, letters, and Language short words but not with verbal response functions of  Split-brain patient V.J.: right hemisphere able to write but not speak the right  Right hemisphere: drawing, puzzles, hemisphere sound nuances  Left hemisphere: language   Left lateral (Sylvian) fissure longer and less steep than right  Geschwind and Levitsky: left Anatomical planum temporal larger than right in 65% cases asymmetry  Functional human asymmetry: and language more than 90% humans right- handed  Animals: equal numbers of right- handers and left-handers   Language studies  Former method: correlate language Language deficits with postmortem analysis of brain damage studies using  Recent techniques: study language function in living humans with brain electrical brain stimulation and PET scans stimulation &  Three main effects of brain brain imaging stimulation on language  Vocalizations, speech arrest, speech difficulties similar to aphasia   In motor cortex: immediate speech arrest Effects of  In Broca’s area: speech arrest brain from strong stimulation, speech hesitation from weak stimulation stimulation on  In posterior parietal lobe near langauge Sylvian fissure and in temporal lobe: word confusion and speech arrest   Ojemann studies: stimulation in Effects of small parts of cortex at different locations in epilepsy patients: brain naming, reading, repeating facial movements stimulation on  Considerable variability in brain langauge areas where electrical stimulation affects language   fMRI (Lehericy and colleagues): record Imaging of during three different language tasks  Activated brain areas consistent with language temporal and parietal language areas processing in  More activity than expected in the human nondominant hemisphere  A: word generation brain  B: passive listening  C: silent sentence repetition   PET scans indicating blood PET imaging flow to different areas of the brain during language tasks of sensation consistent with neuroanatomical & speech understanding of sensory / motor processing localization   Multiple brain areas critical for language, not just Broca’s and Wernicke’s areas  Brain imaging and stimulation studies have revealed widespread brain areas in both hemispheres involved in language. Summary  Language processing involves a collection of interacting subsystems for different language skills.  Many different components: understanding word sounds, meanings of words, grammar, naming objects, producing speech, and more Quiz hint!  Aphasia types & their symptoms / causes Questions?