SLH 371 Spring 2025 - Neural Basis of Language

Learning Objectives

  • List areas within the perisylvian region that are important for language processing
  • Compare and contrast classical and dual-path models for language processing
  • Describe how language changes with typical aging
  • Discuss how language processing differs in multilingualism

Models of Language Processing

  • Language:
    • A finite set of arbitrary symbols, agreed upon by a community or society, which can be combined to communicate an infinite number of concepts between community members for social cooperation (Andreatta, 2022)

Receptive & Expressive Language

  • RECEPTIVE
    • Understanding language
  • EXPRESSIVE
    • Producing language

Language Functions

  • Language functions
    • Phonological processing
    • Lexical & semantic processing
    • Syntactic processing
    • Pragmatics
    • Cognitive-executive control
    • Verbal working memory
  • NOT language function:
    • Sensory processing (hearing, vision, tactile)
    • Speech production (after the message has been formulated)

The Perisylvian Region

  • Region surrounding sylvian fissure (lateral sulcus)
  • Left > Right hemisphere activated during receptive and expressive language

Classical Model of Language Processing: Wernicke-Geschwind Model

  • Based on observations by Paul Broca, Carl Wernicke, and Norman Geschwind
    • Broca’s area
      • Inferior frontal gyrus
      • Center for spoken language production and articulation
    • Wernicke’s area
      • Posterior superior temporal lobe
      • Center for spoken language comprehension
    • Arcuate fasciculus
      • White matter connection between Broca’s & Wernicke’s areas
    • Primary auditory cortex
      • Primary input pathway
    • Integrative areas
      • Supramarginal & angular gyri
    • Primary motor cortex
      • Output pathway to primary motor cortex

Problems with the Classical Model

Dual-Path Model of Language Processing

  • Several models, all emphasizing importance of white-matter connections between gray matter processing hubs
  • Pathways and regions support both comprehension and production
    • Dorsal
      • Regions: Parietal & frontal lobes
      • Connections: Arcuate fasciculus & superior temporal fasciculus
      • Important for auditory-motor integration
    • Ventral
      • Regions: Temporal & frontal lobes
      • Connections: Uncinate & inferior fronto-occipital fasciculi, extreme capsule
      • Important for semantic and syntactic processing

The “truth” is likely still more complicated

But - as SLPs, what do we need to keep in mind?

Age Effects on Language

Why do we care?

  • Numbers 2022: 57.8 million ≥≥ 65y
  • 2040: 78.3 million ≥≥ 65y
  • 2060: 88.8 million ≥≥ 65y
  • Impacts of age
    • 33% of Americans ≥≥ 65y report disability
    • Health conditions related to acquired communication & swallowing difficulties increase sharply with age
    • Source: acl.gov

An Aging Nation

  • For the First Time in U.S. History Older Adults Are Projected to Outnumber Children by 2034

Understanding how functions change with age will help us identify differences from disorders

Language Processing in Healthy Aging

  • Semantics
    • Intact or improved semantic systems
  • Lexical/phonological retrieval
    • Slower rate
    • Increased pauses & fillers
    • Increased “tip of the tongue” experiences
  • Comprehension
    • Mixed findings, but some studies report slowed comprehension
  • Reading
    • Read aloud more slowly in the context of unpredictable distractions
  • Supralinguistic
    • More off-topic conversational statements
  • Language network
    • More distributed cortical network
    • Lower levels of functional activation
    • Rossi & Diaz (2016), Burke & Shafto (2014)

Multilingualism

Multilingual Language Processing

  • Language co-activation
    • Multilinguals cannot fully “turn off” their languages in production or comprehension
    • Languages compete for selection
    • Thus, multilinguals use complex cognitive processing for monitoring and controlling activation of language networks
      • Pre-frontal cortex, anterior cingulate gyrus, basal ganglia
    • Languages are not equally proficient in all contexts in an individual
    • Considerable between-individual variability
    • Learning an additional language (at any age) requires substantial neuroplasticity
      • Changes in amount, location, and strength of synapses
    • Rossi & Diaz (2016)

Differences in Multilinguals

  • Improved executive functioning
  • Cognitive control
  • Working memory
  • Selective attention
  • Structural differences
    • Increased grey matter density in older, bilingual adults
  • Cognitive reserve
    • E.g., delay of up to 4 years of cognitive symptoms due to Alzheimer’s disease
    • Rossi & Diaz (2016)

Summary

  • Language function is distributed in the brain, with many bilateral regions activated
    • Primarily Left perisylvian region
  • As tools for measuring brain function improve, our understanding of neural mechanisms change
  • Language control changes with aging and multilingualism
  • Likely related to cognitive function