LIN175-Midterm3-Prep

Study Guide: Neurobiology of Language Midterm

Neurological Basis of Language Disorders

• Differences between aphasia and motor speech impairments (e.g., Broca’s vs. Wernicke’s vs. Conduction aphasia)
  • Language disorders can arise from many different problems:
    • Broca’s: Speech production. Broken / difficulty producing words. Non fluent aphasia.
    • Wernicke’s: Speech comprehension. Fluent aphasia. Nonsense
    • Conduction Aphasia: Language comprehension mostly intact, but production is distorted by phonemic paraphasias and repetition is severely compromised.
      • 2 theories (W.L. model and 2 pathways)

        • Disconnection syndrome

        • Impaired transfer of acoustic image of words to motor programs via arcuate fasciculus

        • Left supramarginal gyrus

        • Interiorly adjacent tissue deep inside the sylvian fissure

          • Damage to sensorimotor interface, area Spt

        • This is different than the claim in the W.L. model, that claims it arises from damage to the arcuate fasciculus

• Selective vocal cord impairment and its effects on speech production
• Speech errors: phonemic vs. semantic paraphasias, neologisms, and tip-of-the-tongue states
  • Phonemic: Substitute phoneme for another (cat -> bat)
  • Semantic: Substitute word for semantically related word (cat -> tiger)
  • Neologistic: Insert strings of speech sounds for a word target (toothbrush -> sez sez sez sez, hospital -> nezaful)

Neural Models of Language Processing

• Wernicke-Lichtheim-Geschwind model
  

  • M: Broca’s
  • B: Concepts (distributed)
  • A: Wernicke’s
  • Disproved because of double dissociation between language comprehension and speech perception
    • Deficit in comprehension: posterior STS (superior temporal sulcus) lesions
    • Deficit in perception: inferior frontal lesion (and parietal)

• Dual-Stream Model (Dorsal vs. Ventral pathways)
  

  • Split into what and where pathways. Similar dorsal/ventral pathways exist in vision
    • Dorsal (upper): Where
      • Sensorimotor articulation
      • Doing things with language
    • Ventral (lower): What
      • Lexical/conceptual processing
        Key to note: The initial auditory processing steps (spectro temporal analysis and phonological network) are processed bilaterally.
  • Spectro Temporal Analysis: Dorsal STG (superior temporal gyrus).
    • Spectrogram analysis of speech? Key part of converting frequencies to phonemes
  • Phonological Network: Mid-post STS (superior temporal sulcus)
  • Conceptual Network: WIDELY distributed across cortex.
  • Ventral Stream: “Where”. Map sound structure to semantic representations. Forms integrated meanings of complex utterances.
    • Combinatorial Network: aMTG/pMTG (anterior middle temporal gyrus), pITG/aITS (anterior inferior temporal gyrus)
      • Higher order region thought to implement a combinatorial network that plays an important role in constructing the integrated meanings of phrases and sentences, drawing upon both semantic and grammatical information.
      • Left hemisphere dominant
      • Not well elaborated on (in the literature)
    • Lexical Interface: pMTG, pITS
      • A relay station to getting from the phonological structures of words to their semantic structures
      • Weak left hemisphere dominance
  • Dorsal Stream: “How”. From sound to action. Mapping perceptual representations of vocal sounds onto motor representations
    • Sensorimotor Interface: Parietal-Temporal Spt? Spt == (Sylvian parietal temporal, located at the parietal temporal boundary, and a subportion of area tpt)
      • Appears to operate as a device for coordinating or translating between the sound based phonological network in the lateral temporal lobe and the motor based articulatory network in the posterior frontal lobe
    • Articulatory Network: pIFG (posterior inferior frontal gyrus), PM (premotor cortex), Anterior Insula
      • Speech production / auditory verbal short term memory (STM) / Speech perception

• The role of Broca’s area, Wernicke’s area, and Middle Temporal Gyrus in language processing

  • Broca’s:
  • Wernicke’s:
  • Middle Temporal Gyrus:

• The function of the lexical interface and the sensorimotor interface in language comprehension

  • Lexical Interface: Sound -> Word representation/Semantic Structures. Bilateral.
    • “What does this sound mean?”
  • Sensorimotor Interface: Sound -> Motor coordination of speech.
    • “How will i move my body to achieve this action?”

• fMRI and PET findings on speech perception and comprehension

  • Helps us to discover which regions correspond to what stimulus
    • Think of a control study for real intelligible vs unintelligible multi word utterances. Will isolate activation to higher level regions (corresponded to meaning)
      • This study found activation in left lateral ATL (anterior temporal lobe)
      • ATL may serve as a semantic hub binding diverse lexical concepts?

Aphasia and Language Processing

• Characteristics of Broca’s aphasia vs. Wernicke’s aphasia
  • Broca’s aphasia
  • Wernicke’s aphasia
• Closed-class lexical deficits and their effects on sentence comprehension
  • Open-class words - nouns, lexical verbs, adjectives, and adverbs
  • Closed-class words - pronouns, determiners, conjunctions, and prepositions
    • Do not readily accept new members, have a finite set
• Tests for phonemic discrimination
• Double dissociation between word comprehension and syllable awareness

Sign Language and the Brain

• How signed languages lead to similar aphasia patterns as spoken languages
  • Similarities: Left centralized. A case study of right hemispheric damage was able to keep language abilities despite having unilateral neglect.
  • Differences
• Differences in left vs. right hemisphere involvement in signed vs. spoken language
  • Highly similar areas in left and right hemisphere (BSL and English)
  • Spoken:
    • Left: Language
      • Speech
      • Reading
    • Right: Spatial information
      • Face recognition
      • Maps/Route
    • Signing:
      • Left: Language
      • Right: Spatial information
• The role of spatial syntax in right hemisphere processing

Language Acquisition and Bilingualism

• Critical period hypothesis for second language learning
• Bilingual brain organization: coordinate, compound, and subordinate bilingualism
  • Compound Bilingual: L1 and L2 are learned concurrently at home.
    • Often mother and father may speak different languages, or family. Language acquired in the same environment
  • Coordinate Bilingual: L2 is learned after L1 (after around school age.)
    • Languages learned in different contexts, home vs school.
  • Subordinated Bilingualism: L1 is dominant and translates in into L2.
    • Weaker language is interpreted through the first
    • You think in L1, and consciously interpret into L2
• How brain damage affects bilingual aphasia recovery
  • Pitres Law: The most familiar language is the one that tends to be recovered
  • Minkowski’s Law: The language with the strongest emotional association is less impaired, and recovers first
  • Recovery Trajectories, will use languages A and B as shorthand:
    • Parallel ()
    • Selective () - B no improvement
    • Differential (). A recovers faster
    • Substantial () - Initial stagnation, but explosive growth later
    • Antagonistic () - One recovers while the other doesn’t, or even worsens
  • Mixed recovery - Inappropriate and unrestricted blending of languages. Suggested to be cognitive control, role of inhibition in Wernicke’s aphasia. Inhibition to select (suppress) a language. Broken “language switch”
• Factors affecting bilingual brain activation

Neuroprosthetics and Language Recovery

• Neuroprosthetic research (NEJM article): brain-computer interfaces for speech restoration in ALS
• How the neuroprosthetic works: decoding neural signals for speech production
• Components of the neuroprosthetic (implantation sites, neural decoding)

Theoretical and Research Considerations

• The role of exploratory research in neurolinguistics (e.g., discovery of N400 & P600 ERPs)
  • N400
  • P600
  • Exploratory research: Creating theories has been difficult, so a lot of research devoted to exploration
• Importance of falsifiability in scientific theories
  • Need to be specific enough to both make predictions and be tested/proven incorrect.
    • Being difficult to disprove is bad
• Use of models in neurolinguistic research
  • Guide research, make predictions, allow interesting questions

Self Study / Notes:

Levels of Analysis:

High to Low:

• Linguistic - High level linguistic structures in the brain, phonological, syntactic, etc.
• Psycholinguistic - Architecture and algorithms in brain and language
• Neurolinguistic - Neurobiological machinery enabling algorithms