Neuroanatomy of Language

Human Vocal Tract and Brain

• The human vocal tract has properties that are useful for rapidly producing different sounds.
• The vocal tract gave humans a survival advantage that compensated for the risk of death from choking on food.

Neuroanatomy and Neurophysiology of Language

• The cerebral cortex controls higher-level functions such as planning and reasoning.
• Sub-cortical structures control lower-level functions such as eating and breathing.
• The corpus collosum is a band of fibers that connects the right and left hemispheres of the brain.
• Contra-lateral connections occur when brain hemispheres are connected to the opposite side of the body.
• Neurons are organized into neural circuits that work together.

Neurolinguistics

• Neurolinguistics is the study of how the brain functions to produce language.
• The goals of neurolinguistic investigations are to discover:
  • The neural anatomy and processes responsible for language.
  • What is distinctive in the human brain that makes language possible.
• The human brain is necessary for language, and the existence of sign languages shows that it is not even necessary.

Methods of Neurolinguistic Investigation

• The lesion method is used to study patients who have suffered injuries to different parts of their brains and determine what functions are impaired as a result.
• The goal is to correlate bits of missing brain with bits of missing psychological functioning.

Multicultural Focus

• Foreign-birth adoption: a child is adopted from overseas, often from an institutionalized setting.
• The language outcomes of these children show variability, in part due to the age at which they were adopted, and in part due to the care they received in their birth country.

Evidence in Support of CP/SP

• Late acquisition of sign language: deaf children who are exposed to sign language from infancy are more proficient than deaf children who exposed to sign language later in childhood.
• Second language acquisition: adults who immigrate to the USA at a younger age sound and perform more like native speakers.

The Genetic Basis of Language Development

• The heritability of individual differences:
  • Individual children's rates of language acquisition do vary, and some variation is genetically heritable.
  • Mono-zygotic (identical) twins show more similar rates of language development than di-zygotic (fraternal) twins.
  • Genetic heritability appears to be stronger for syntactic than lexical development.
• The genetics of language impairment:
  • Language impairment appears to have a strong genetic component, as found in twin studies and adoption studies.
  • Language impairment runs in families.
  • Studies of the KE family have suggested a particular gene, FOXP2, is critical for typical language development.

Individual and Sex-related Differences in Brain Organization

• Although 80-98% of the population is left-hemisphere dominant for language, not all people are, and there is some variation in the degree of dominance.
• Left-handed people and women tend to show more bilateral processing of language.

Brain Development and Language Development

• The development of the left-hemisphere specialization for language:
  • Equipotentiality hypothesis: at birth both hemispheres have the potential to host language ability, and specialization occurs as a function of experience.
  • Invariance hypothesis: the left hemisphere has the adult specialization for language from birth, and maturation has no effect on specialization.
• A lot of research support the invariance hypothesis.