Lecture 13 Language

Language

Goals

  • Reconnect with concepts of localization of function, modularity, and connectionism in the context of language.
  • Introduce the language system from a neuropsychological perspective.
  • Examine the influence of brain injuries on language processing.
  • Explore plasticity in the neural basis of language acquisition.

Historical Context of Language Studies

  • Edwin Smith Papyrus (3000 BC):
    • Described cases of paralysis and aphasia in battle-injured soldiers.
    • Early observations of brain-behavior relationships.
  • Paul Broca (1861):
    • Discovered Broca’s area in the left frontal lobe associated with speech production deficits.
    • Studied a patient known as “Tan,” who could only say one word.
  • Carl Wernicke (1874):
    • Identified Wernicke’s area in the posterior temporal lobe, associated with speech comprehension deficits.

Components of Language

  1. Speech Reception: Processing spoken words (auditory system).
  2. Speech Production: Generating spoken language (motor system).
  3. Prosody: Emotional and melodic aspects of speech.
  4. Reading and Writing: Visual and motor systems.
  5. Semantics and Syntax:
    • Semantics: Meaning of words and sentences.
    • Syntax: Rules for combining words into grammatically correct sentences.

Language Disorders (Aphasias)

Broca’s Aphasia (Non-Fluent Aphasia)

  • Characteristics:
    • Difficulty speaking; slow, deliberate speech.
    • Agrammatical; uses content words only (e.g., “son college”).
    • Difficulty understanding complex syntax (e.g., “The boy was hit by the girl”).
  • Neurological Basis:
    • Left inferior frontal lobe lesion, often due to middle cerebral artery stroke.
  • Case Studies:
    • Broca’s original patient “Tan.”
    • Modern video examples demonstrate halting, effortful speech.

Wernicke’s Aphasia (Fluent Aphasia)

  • Characteristics:
    • Fluent but nonsensical speech with paraphasias (word substitutions or neologisms).
    • Severe comprehension deficits; patients often unaware of their condition (anosognosia).
  • Neurological Basis:
    • Lesions in the posterior left temporal lobe.

Conduction Aphasia

  • Characteristics:
    • Fluent speech with frequent paraphasias.
    • Poor repetition; aware of errors and attempts self-correction.
  • Neurological Basis:
    • Damage to the arcuate fasciculus connecting Broca’s and Wernicke’s areas.

Pure Alexia (Alexia Without Agraphia)

  • Characteristics:
    • Letter-by-letter reading with finger tracing.
    • Patients can write but cannot read what they wrote.
  • Neurological Basis:
    • Lesions in the left occipitotemporal region.
    • Considered a disconnection syndrome.

Gerstmann’s Syndrome

  • Characteristics:
    • Agraphia (writing disability).
    • Acalculia (difficulty with arithmetic).
    • Finger agnosia (inability to identify fingers).
    • Right-left disorientation.
  • Neurological Basis:
    • Damage to the left angular gyrus.

Neurological Basis of Language

Brain Regions

  • Broca’s Area: Speech production and syntax.
  • Wernicke’s Area: Speech comprehension.
  • Arcuate Fasciculus: Connects Broca’s and Wernicke’s areas; critical for repetition.
  • Angular Gyrus: Involved in reading and writing.
  • Occipitotemporal Cortex: Visual word form area critical for reading.

Functional Neuroimaging

  • fMRI Studies:
    • Show activation in Broca’s area during syntax processing.
    • Left occipitotemporal activation during word recognition tasks.
  • Electrophysiology:
    • Reveals distinct responses in visual areas for letter strings vs. faces.

Evolution of Language

FOXP2 Gene

  • Found in humans and songbirds; critical for motor control and vocal learning.
  • In Songbirds:
    • FOXP2 affects song learning, motor timing, and sequencing.
  • In Humans:
    • Mutation in FOXP2 linked to speech and language disorders (e.g., KE family).

Mirror Neurons

  • Discovered in area F5 of monkeys (analogous to Broca’s area).
  • Fire during action performance and observation.
  • Suggested link to the evolution of gestural communication as a precursor to spoken language.

Key Concepts in Language Processing

  1. Acoustic and Visual Processing:
    • Spoken Language: Involves acoustic analysis, phoneme recognition, and lexical access.
    • Written Language: Visual analysis leads to orthographic and semantic processing.
  2. Perceptual Narrowing:
    • Infants initially recognize all phonemes but lose sensitivity to non-native phonemes over time.
  3. Hemispheric Specialization:
    • Left Hemisphere: Dominant for words and syntax.
    • Right Hemisphere: Processes prosody and emotional tone.

Study Insights and Applications

  • Language Plasticity:
    • Neural reorganization allows recovery of language functions after injury, especially in younger individuals.
  • Disconnection Syndromes:
    • Highlight the importance of white matter tracts in integrating modular brain regions for language.
  • Clinical Implications:
    • Understanding aphasias aids in diagnosis, treatment, and rehabilitation planning.

Key Terms

  • Aphasia: Loss of ability to understand or produce speech.
  • Paraphasia: Speech errors such as word substitutions.
  • Orthography: Visual representation of language (letters, words).
  • Prosody: Rhythmic and intonational aspects of speech.
  • FOXP2: Gene associated with speech and language capabilities.

This summary integrates historical, anatomical, and clinical insights into language processing, offering a comprehensive resource for understanding the neural basis of language and its disorders.

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