The Brain & Language

The Brain & Language

1. 2 ways we can investigate this:

   • 2) Brain maturation and development - the appearance of behaviours can tell us about adult cognition
   • 1) Lesion Studies - modularity of language subprocesses - necessity and sufficiency of brain regions for language

2. Brain regions involved in language

   • BROCA'S AREA
     • Cortical region in the POSTERIOR portion of the LEFT INFERIOR FRONTAL GYRUS
       • Long thought to be involved in the PRODUCTION OF SPEECH
   • WERNICKE'S AREA
     • SUPERIOR & POSTERIOR region of the LEFT TEMPORAL LOBE
       • Involved in LANGUAGE COMPREHENSION
   • ARCUATE FASILCULUS (AF)
     • A WHITE MATTER TRACT connecting WERNICKE'S and FRONTAL PREMOTOR / MOTOR areas. Connections are bidirectional

3. The Aphasias

   • Broca's Aphasia
     • Marked by a DEFICIT in the PRODUCTION of FUNCTION WORDS. Nouns and verbs are better preserved.
       • Articulation is OK but WRITING IS IMPAIRED
         • DEFICIT IN GRAMMAR PRODUCTION
   • Wernicke's Aphasia
     • Impaired GRAMMATICAL COMPREHENSION, accompanied by the production of FLUENT but UNGRAMMATICAL speech
       • Phoneme perception and semantic priming are normal
   • Conduction aphasia
     • A language disturbance characterised by fulent spontaneous speech, good comprehension but POOR REPETITION associated with ABUNDANT PHONOLOGICAL PARAPHASIAS (incoherent words substituted for intended words)

4. THE CLASSIC MODEL OF LANGUAGE PROCESSING IN THE BRAIN

   • Geschwind (1972)
     • Input into sensory areas > relayed to Wernicke's areas > then to Broca's area > finally to the motor cortex
       • POSTERIOR INPUT, ANTERIOR OUTPUT
   • Suggest compartmentalised regions of the brain

5. Do experiments support /challenge this model?

   • Wernicke's input / comprehension, Broca's output / production?
     • CARAMAZZA & ZURIF (1976)
       • Studied patients with damage to Broca's area, Wernicke's area or the AF
         • Task: Choose a picture that corresponds to the scenario
           • 1) The book the girl is reading is yellow. 2) The horse that the bear is kicking is brown
             • Semantics help disambiguate 1 (Girls are rarely yellow), but help less with 2, thus rely on syntax
               • Broca's area and AF pateitns - deficits in SYNTACTICAL comprehension (sentence 2)
                 • This DISAGREES with the model because it doesn't fit with the conceptualisation that BROCA'S AREA IS THE OUTPUT PRODUCTION
   • DRONKERS AND WILKINS (2004)
     • 64 Lesion patients
       • Evaluated them for AUDITORY LANGUAGE COMPREHENSION
         • Took BRAIN IMAGES of LESIONS and OVERLAYED them
           • Found that there were many brain regions outside of the classically defined areas were involved in language comprehension deficits. This contradicts the model
   • The right hemisphere also contributes to language
     • Language is lateralised and usually depends most on the LH but RELATIVE PERFORMANCE DIFFERENCES are seen with SIDE of PRESENTATION
       • Word - non-decison task. Present in LVF or RVF
         • People are faster when word is presented to LH (right ear) but can still be done in RH
           • Dichotic listening - when different words are presented. Most individuals only report hearing what is presented in the right ear (LH) - LH is more involved?
     • Split Brain Connection Syndrome
       • RVF naming objects
         • RH processes linguistic input and recognise when the right object is found. Some limited linguistic knowledge - LEXICAL
     • RH activation is also seen in brain imaging studies of language
       • RH is involved in processing certain ASPECTS of PROSODY, patterns of rhythm / inflections of speech e.g. sarcasm
         • Comprehending humour (Bihrle et al 1986)

6. AN ALTERNATIVE MODEL OF LANGUAGE IN THE BRAIN

   • Phonology - Phonemic (smallest units of meaning) and phonetic (sounds) aspects of speech.
     • Anterior lesions associated with deficits in phonetic control - different phoneme being substituted e.g. aspirated p as in 'pill' when trying to say 'spill'. Posterior lesion leads to inappropriate phoneme
   • Syntax - rules governing how words are put together in sentences
     • Anterior aphasia - deficit in ability to produce and comprehend the grammatical aspects of language
   • Semantics (meaning of words and word combinations)
     • Posterior aphasia patients have deficits
       • Posterior input, Anterior output. Posterior semantic, Anterior syntactic
         • DOUBLE DISSOCIATION OF LANGUAGE PROCESSES
           • However, data from patients isn't as clean. It doesn't always fall neatly into these divisions

7. How to model language in the brain

   • Instead, NETWORKS of brain regions may be the best way to characterise how the brain processes language
     • VIGNEAU et al (2006)
       • Meta-analysis of 129 imaging studies to identify phonological, semantic and sentence processing networks
         • Brain regions separated in space but active in concert - argues a LARGE-SCALE ARCHITECTURE OF NETWORKS rather than MODULAR ORGANISATION of language in the LH

8. Most aspects of language processing involve NETWORKS that span the anterior and posterior areas

   • A number of regions are thought to be involved in more than one type of process, which makes sense because we need to join these aspects of language everyday. The smooth functioning of the language system requires INTEGRATION.