Language

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Language

  1. 1. Language & the Brain
  2. 2. What is Language? <ul><li>A system by which sounds, symbols, and gestures are used for communication </li></ul><ul><li>Sensory/Motor Convergence </li></ul><ul><ul><li>Language enters the brain through sensory inputs (vision, hearing – touch?) </li></ul></ul><ul><ul><li>Produces motor responses  speech, writing </li></ul></ul><ul><ul><li>Processing between sensory and motor systems is the essence of language </li></ul></ul>
  3. 3. For Discussion <ul><li>Is language universal in human society? </li></ul><ul><li>Is language universal among animals? </li></ul><ul><li>Can animals be taught human language? </li></ul><ul><li>How we define language effects our answers  </li></ul><ul><ul><li>Language = communication </li></ul></ul><ul><ul><li>Language (human) is a complex system that employs predictable rules (grammar) </li></ul></ul>
  4. 4. Animals & Language <ul><li>Many animals use specific vocalizations to communicate  claim territory, warn of danger, attract a mate </li></ul><ul><ul><li>Communication is limited, specific, stereotypical </li></ul></ul><ul><li>Human language is a creative process </li></ul><ul><ul><li>The possibilities are effectively endless, limited only by the rules of grammar </li></ul></ul>
  5. 5. Animals & Language <ul><li>Nim Chimpsky </li></ul><ul><li>Washoe </li></ul><ul><ul><li>Chimps raised in human families; taught American sign language </li></ul></ul><ul><li>Koko </li></ul><ul><ul><li>A lowland gorilla, learned more than 1000 words in American sign language and understood at least 2000 </li></ul></ul><ul><ul><li>Demonstrated complex grammar use </li></ul></ul>Can animals “learn” human language, or rules of grammar?
  6. 6. Koko
  7. 7. Historical Perspective <ul><li>Greek & Roman Empires </li></ul><ul><ul><li>Thought that the tongue controlled speech </li></ul></ul><ul><li>Sixteenth century: </li></ul><ul><ul><li>Discovered that speech impairment did not reflect tongue paralysis </li></ul></ul><ul><li>Johann Gesner – 1770 </li></ul><ul><ul><li>Inability to associate images or abstract ideas with their expressive verbal symbols </li></ul></ul><ul><ul><li>Attributed to brain damage from disease </li></ul></ul><ul><ul><li>Cognitive ability may be intact but verbal expression is lost </li></ul></ul><ul><ul><li>The first steps toward modern understanding of aphasia </li></ul></ul>
  8. 8. Historical Perspective <ul><li>Franz Joseph Gall & phrenology </li></ul><ul><ul><li>Speech loss while other mental faculties are retained suggests that there is a specific brain area devoted to speech </li></ul></ul><ul><li>Jean Baptiste Bouillard – 1825 </li></ul><ul><ul><li>Speech is controlled by the frontal lobes </li></ul></ul><ul><li>Simon Alexandre Aubertin – 1861 </li></ul><ul><ul><li>Described a man who had shot away his frontal bone in a failed suicide attempt </li></ul></ul><ul><ul><li>Pressing a spatula against the exposed brain tissue halted speech, which resumed immediately when the pressure was released </li></ul></ul>
  9. 9. Broca’s Area <ul><li>Paul Broca – 1861 </li></ul><ul><ul><li>With Aubertin, examined the brain of a man unable to speak </li></ul></ul><ul><ul><li>Found lesion in the frontal lobes </li></ul></ul><ul><li>Published a study of 8 similar patients in 1863 </li></ul><ul><ul><li>Showed that language expression is controlled by a portion of the frontal lobe in one hemisphere, usually the left </li></ul></ul><ul><li>First clear demonstration that brain function can be localized </li></ul><ul><li>Now called Broca’s area </li></ul>
  10. 10. Broca’s Area
  11. 11. The Wada Procedure <ul><li>A simple procedure to study the function of a single cerebral hemisphere </li></ul><ul><li>Fast acting barbiturate is injected into the carotid artery on one side </li></ul><ul><ul><li>Preferentially carried to the ipsilateral hemisphere </li></ul></ul><ul><ul><li>Acts as a short-term anesthetic </li></ul></ul><ul><ul><li>Limbs on the contralateral side become paralyzed </li></ul></ul><ul><li>Can then assess patients’ ability to speak </li></ul><ul><ul><li>If the injection is on the side dominant for speech, patient is completely unable to talk </li></ul></ul><ul><ul><li>Opposite side retains complete speech ability </li></ul></ul>
  12. 12. Handedness <ul><li>Handedness is an obvious functional asymmetry </li></ul><ul><li>90% of people are right handed </li></ul><ul><ul><li>Left hemisphere specialized for fine motor control </li></ul></ul><ul><ul><li>Other species show about equal numbers of left and right handers </li></ul></ul><ul><li>The left hemisphere is dominant in speech in 96% of right handed people and 70% of left-handed people </li></ul><ul><ul><li>Thus the left hemisphere is dominant for language in 93% of people </li></ul></ul><ul><ul><li>Bilateral representation of speech occurs only in left-handers </li></ul></ul>
  13. 13. Wernicke’s Area <ul><li>Karl Wernicke – 1874 </li></ul><ul><li>Reported that lesions in the left hemisphere in a region distinct from Broca’s area disrupt speech </li></ul><ul><li>Located on the superior surface of the tempora; lobe between the auditory cortex and the angular gyrus </li></ul><ul><li>Effect of damage to Wernicke’s area is different from that associated with Broca’s area </li></ul>
  14. 14. Broca’s & Wernicke’s Speech Centers <ul><li>Borders of both areas are diffuse, not clearly defined </li></ul><ul><li>Areas vary from one person to another </li></ul><ul><li>Each may be involved in more than one language function </li></ul>
  15. 15. Components of the Language System
  16. 16. Aphasia <ul><li>Partial or complete loss of language function following brain damage </li></ul><ul><li>Much of what we know about language and the brain comes from studying patients with specific deficits </li></ul><ul><li>The occurrence of distinct types of aphasia suggests that language is processed in several stages at several locations in the brain. </li></ul>
  17. 17. Types of Aphasia
  18. 18. Broca’s Aphasia <ul><li>Also known as motor or nonfluent aphasia </li></ul><ul><li>Person has difficulty speaking, although they can understand both spoken and written language </li></ul><ul><li>People with Broca’s aphasia often pause, searching for the right word </li></ul><ul><ul><li>Anomia – inability to find the right word </li></ul></ul><ul><li>Telegraphic speech using only content words </li></ul><ul><ul><li>agrammatism </li></ul></ul><ul><ul><li>use nouns verbs & adjectives </li></ul></ul><ul><ul><li>omit function words – articles, pronouns conjunctions </li></ul></ul>
  19. 19. Wernicke’s Aphasia <ul><li>Clearly different from Broca’s aphasia </li></ul><ul><li>Speech is fluent but comprehension is poor </li></ul><ul><li>Content does not make sense </li></ul><ul><ul><li>Mixtures of clarity & gibberish </li></ul></ul><ul><li>More paraphasic errors </li></ul><ul><ul><li>Substitution of incorrect sounds, sound-alike words </li></ul></ul><ul><li>Seem undisturbed by their own speech </li></ul><ul><li>Comprehension, such as following directions, is lost </li></ul><ul><li>Written language, music are similarly affected </li></ul>
  20. 20. Implication’s of Wernicke’s Aphasia <ul><li>Wernicke’s area is located on the superior temporal gyrus near the primary auditory cortex </li></ul><ul><li>May play a critical role in relating incoming sounds to their meaning </li></ul><ul><li>Stores memories of the sounds that make up words </li></ul>
  21. 21. Wernicke-Geshwind Model <ul><li>A model for language processing in the brain </li></ul><ul><li>System includes: </li></ul><ul><ul><li>Wernicke’s area </li></ul></ul><ul><ul><li>Broca’s area </li></ul></ul><ul><ul><li>The articulate fasiculus </li></ul></ul><ul><ul><li>(a bundle of axons connecting the two) </li></ul></ul><ul><ul><li>The angular gyrus </li></ul></ul><ul><li>Model is an oversimplification, but generally descriptive of language processing </li></ul>
  22. 22. Repetition of Spoken Words <ul><li>Pathway: </li></ul><ul><ul><li>Sounds of incoming speech reach the ear </li></ul></ul><ul><ul><li>Auditory system processes the sounds </li></ul></ul><ul><ul><li>Neural signals reach the auditory cortex </li></ul></ul><ul><li>Wernicke-Geshwind model says that sounds are not understood as words until they are processed in Wernicke’s area </li></ul><ul><li>To repeat the words the signal is passed to Broca’s area via the articulate fasciculous </li></ul><ul><ul><li>Broca’s area converts words to code for muscle movement </li></ul></ul><ul><ul><li>Sends message to motor cortex for lips, tongue, etc. </li></ul></ul>
  23. 23. Wernicke-Geshwind Model Repeating a Spoken Word
  24. 24. Reading Written Text Aloud <ul><li>Incoming information is processed by the visual system </li></ul><ul><ul><li>Striate cortex & higher-order visual cortical areas </li></ul></ul><ul><li>Signals are passed to the angular gyrus </li></ul><ul><li>In the cortex of the angular gyrus, the output evokes the same activity as if the words were spoken </li></ul><ul><li>Process is now the same as the first example </li></ul><ul><ul><li>Wernicke’s area  Broca’s area  motor cortex </li></ul></ul>
  25. 25. Wernicke-Geshwind Model Repeating a Written Word
  26. 26. Conduction Aphasia <ul><li>A lesion disconnects Wernicke’s area from Broca’s area, but leaves both intact </li></ul><ul><ul><li>Usually involves damage to the parietal cortex and the arcuate fasciculus </li></ul></ul><ul><li>Comprehension is good and speech is fluent </li></ul><ul><li>Difficulty is in repeating words </li></ul><ul><ul><li>Greatest difficulty with function words, nonsense sounds </li></ul></ul><ul><li>Comprehends sentences they read aloud, though spoken words contain errors </li></ul>
  27. 27. Aphasia in Bilinguals <ul><li>If an individual is bilingual, does a stroke produce aphasia for both languages? </li></ul><ul><li>Depends on order learned and relative fluency </li></ul><ul><li>If languages were learned to same level of fluency at about the same time, both are equally affected </li></ul><ul><li>Language is better preserved in the language learned more fluently and/or earlier in life </li></ul><ul><li>If learned at different times, one will be affected more than the other </li></ul><ul><li>Suggests that a second language may use a different population of neurons </li></ul>
  28. 28. Aphasia in the Deaf <ul><li>Left hemispheric lesions cause a language deficit in deaf subjects who use American Sign Language, similar to verbal aphasics </li></ul><ul><li>Conditions analogous to both Broca’s and Wernicke’s aphasia exist </li></ul><ul><li>Suggests universality of language processing in the brain </li></ul>
  29. 29. Model of Language Processing
  30. 30. Split Brain Studies <ul><li>Corpus callosum is severed to treat seizures </li></ul><ul><li>Hemispheres may retain some communication via the brain stem and smaller commisures </li></ul><ul><li>No significant impact observed in animal studies </li></ul><ul><li>Humans are different </li></ul><ul><li>Asymmetry in ability to verbalize answers to questions perceived by the different hemispheres </li></ul><ul><li>Demonstrated by presenting visual stimuli to one hemisphere </li></ul>
  31. 31. Visual Stimulation of One Hemisphere
  32. 32. Asymmetrical Visual Stimulation <ul><li>Only the right hemisphere sees objects to the left of the point of fixation and vice versa </li></ul><ul><ul><li>True as long as the eyes can’t move to bring images together in the fovea </li></ul></ul><ul><li>Pictures or words are flashed for a fraction of a second </li></ul><ul><ul><li>Shorter than time needed to move the eyes </li></ul></ul><ul><li>Numbers, words, & pictures presented to the right visual field are repeated/described easily; on the left they cannot be described </li></ul><ul><li>Objects manipulated with the right hand can be described; objects in the left hand cannot </li></ul>
  33. 33. Language on the Right Side of the Brain
  34. 34. Functional Asymmetry <ul><li>Deficit is speech specific, not language specific </li></ul><ul><ul><li>Can read and understand letters and numbers with the right hemisphere if the response is nonverbal. </li></ul></ul><ul><ul><li>Patient “says” he sees nothing - but successfully picks matching card </li></ul></ul><ul><li>Some patients can write with the right hemisphere </li></ul><ul><li>Right brain can understand complex pictures </li></ul><ul><li>Right brain can be shown to dominate certain tasks such as perspective and complex puzzles </li></ul><ul><li>The 2 hemispheres can function as independent brains that have different language abilities </li></ul>
  35. 35. Anatomical Asymmetry <ul><li>If function differs, does structure differ between the hemispheres? </li></ul><ul><li>Most significant difference is in the planum temporale on the superior surface of the temporal lobe </li></ul><ul><ul><li>Larger on the left side than on the right in about 65% of brains </li></ul></ul><ul><ul><li>In some cases 5x larger </li></ul></ul><ul><li>Larger even in prenatal development, so not the result of use </li></ul><ul><li>Relationship to language asymmetry uncertain </li></ul>
  36. 36. Asymmetry of the Sylvian Fissure <ul><li>In most right-handed people, Sylvian fissure is longer on the left hemisphere than on the right </li></ul><ul><li>Runs at a more shallow angle </li></ul>
  37. 37. Brain Stimulation and Language <ul><li>Wilder & Penfield </li></ul><ul><ul><li>Electrical stimulation at different cortical sites without general anesthesia (patients are conscious) </li></ul></ul><ul><li>Stimulation of motor cortex in area that controls mouth and lips caused speech arrest </li></ul><ul><ul><li>Occurred with stimulation on either side of the brain </li></ul></ul><ul><li>Stimulation of Broca’s area (left hemisphere only) </li></ul><ul><ul><li>Speech stopped, or with weaker stimulation, was hesitant </li></ul></ul><ul><ul><li>Mild transient anomia </li></ul></ul><ul><li>Stimulation of 2 other sites also affected speech </li></ul><ul><ul><li>In the area of Wernicke’s area and the arcuate fasciculus </li></ul></ul>
  38. 38. Further Electrical Stimulation Studies <ul><li>George Ojemann - building on Wilder and Penfield </li></ul><ul><ul><li>Stimulation of small parts of the cortex at specific locations interferes with reading, naming, or repetition of facial movements </li></ul></ul><ul><ul><li>Different results are obtained at nearby stimulation sites </li></ul></ul><ul><ul><li>Similar results are obtained at distant sites </li></ul></ul><ul><li>Suggests language areas are more complex than Werrnicke-Geshwind model </li></ul><ul><ul><li>Cortical areas other than Broca’s area and Wernicke’s area are involved in language </li></ul></ul><ul><ul><li>Also the thalamus and striatum </li></ul></ul><ul><ul><li>Specialized areas may also exist within Wernicke’s and Broca’s areas </li></ul></ul>
  39. 39. PET Imaging of Language <ul><li>Researchers studied differences in brain activity between sensory responses to words and production of speech </li></ul><ul><ul><li>Either listened to words that were read or looked at words flashed on a monitor </li></ul></ul><ul><ul><li>Measured blood flow levels corresponding to the sensory input </li></ul></ul><ul><li>Visual stimuli showed increased activity in the striate cortex and extrastriate cortex </li></ul><ul><ul><li>Did not respond to auditory or visual stimuli that were not words </li></ul></ul><ul><li>Auditory stimuli also showed activity in the primary and secondary auditory cortex </li></ul><ul><li>No increased activity in Wernicke’s area or the angular gyrus </li></ul>
  40. 40. PET and Word Repetition <ul><li>Repetition requires the subject to first see or hear the word </li></ul><ul><li>Thus it requires both brain areas for the perceptual process as well as those for speech </li></ul><ul><li>To isolate speech, subtracted the components found with the simple sensory task previously described </li></ul><ul><ul><li>Speaking words = repeating spoken words - listening to words </li></ul></ul><ul><li>Shows high activity in the primary motor cortex and supplementary motor area </li></ul><ul><li>Also increased activity around Sylvian fissure near Broca’s area </li></ul><ul><li>Increased activity was bilateral </li></ul>
  41. 41. PET and Word Content <ul><li>For each word, subject stated a use </li></ul><ul><ul><li>Cake -> eat </li></ul></ul><ul><ul><li>Task required thinking and comprehending, as well as speaking </li></ul></ul><ul><li>To isolate verb-noun association, results from just speaking the word were subtracted </li></ul><ul><li>Activated left inferior frontal area, anterior cingulate gyrus, and posterior temporal lobe </li></ul><ul><ul><li>Frontal & temporal cortex are thought to be associated with word association task </li></ul></ul><ul><ul><li>Cingulate cortex may be related to attention </li></ul></ul>
  42. 42. <ul><li>PET IMAGING </li></ul><ul><li>(a) Listening to words </li></ul><ul><li>(b) Speaking words </li></ul><ul><li>(c) Generating verbs </li></ul>
  43. 43. Conclusions from PET Imaging <ul><li>PET results are consistent with language areas determined from studies of aphasia </li></ul><ul><li>PET & fMRI studies show similarities in processing of spoken language, sign language and Braille </li></ul><ul><li>All studies indicate that language processing involves complex mechanisms beyond interaction between the 2 major language areas </li></ul><ul><li>This is the subject of ongoing research </li></ul>

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