Language in the Brain

• Broca's aphasia

  • Slow, laboured speech output
  • Problems with grammar in production and comprehension
  • Some degree of anomia
  • Paraphasic errors: substituting incorrect speech sounds
  • Telegraphic speech (no ifs, thens, ands, thes, buts, whens etc)
  • Repetition of multisyllabic words impaired
  • Aware of deficit and easily frustrated
• Agrammatism


  • Difficulties understanding and producing grammatically 'difficult' utterances (such as the passive voice)
  • Telegraphic speech is a manifestation of this deficit in production
  • Failure to properly use verbs (frequently not conjugated)
• Wernicke's aphasia


  • Problems understanding spoken and written language
  • Speech is fluent with normal grammar, apparently normal stress and intonation, but meaningless/nonsensical
  • Phonemic and semantic paraphasia (substituting words for others with related meanings, e.g., dog for cat; not always possible to tell whether this has occurred or not)
• Wernicke's area


  Posterior part of the superior temporal gyrus
• Wernicke found that patients with this form of aphasia tended to have damage located in the posterior part of the superior temporal gyrus
• Broca's aphasia Summarised


  • Main site of damage: Inferior frontal gyrus (Broca's area) and nearby regions
  • Comprehension: Good (except for complex grammatical structures)
  • Speech: Nonfluent, agrammatical
  • Repetition: Impaired (multisyllabic words)
  • Paraphasia: YES (phonemic)
• Wernicke's aphasia

  • Main site of damage: Posterior temporal lobe (Wernicke's area and nearby regions)
  • Comprehension: Poor
  • Speech: Fluent, grammatical, meaningless
  • Repetition: Impaired
  • Paraphasia: YES (phonemic, semantic)
• Conduction aphasia summarised


  • Main site of damage: Arcuate fasciculus (other regions?)
  • Comprehension: Good (normal)
  • Speech: Fluent (almost normal)
  • Repetition: Impaired (reading aloud and speech)
  • Paraphasia: YES (esp. when repeating/reading aloud)
• Global aphasia summarised

  • Main site of damage: Temporal & frontal areas incl. (but not restricted to) Broca's and Wernicke's areas
  • Comprehension: Poor
  • Speech: Very little
  • Repetition: Impaired
  • Paraphasia: Too little speech to determine
• The Wernicke-Geschwind model describes how different regions/structures with different functional roles interact in the production and comprehension of language (particularly speech)
• Wernicke-Geschwind model


  • Includes both Broca's and Wernicke's areas
  • Broca's area is involved in the planning of language
  • Wernicke's area is involved in the comprehension of language and processing of meaning
  • Auditory cortex is involved in sensory processing of speech sounds
  • Motor cortex is involved in the production of articulatory movements
  • The arcuate fasciculus is a bundle of axons that links Wernicke's and Broca's area
• Repeating spoken words


  1. The auditory cortex processes the speech sounds

  2. Meaning is accessed in Wernicke's area

  3. Signals are transmitted via the arcuate fasciculus to Broca's area

  4. Broca's area accesses/forms a speech-type representation of the word

  5. Instructions are sent to the motor cortex to execute action
• Repeating written words


  1. Written word is processed by the visual cortex

  2. Information is transmitted to the angular gyrus

  3. The visual code of the written word is converted into a phonological code in the angular gyrus

  4. The phonological representation is interpreted in Wernicke's area

  5. 5, 6, 7. Same as 3, 4, 5 in the first example
• The arcuate fasciculus connects Wernicke's and Broca's areas
• Without the connection of the arcuate fasciculus, it would be impossible to read out loud, to repeat what someone said to you
• Wernicke himself predicted that if a stroke or some trauma damaged the arcuate fasciculus then a type of aphasia with a distinct deficit pattern should result
• Comprehension and production should be unaffected in conduction aphasia, but reading and repetition of speech should be disrupted
• Conduction aphasia is commonly associated with damage to the arcuate fasciculus
• The Wernicke-Geschwind model is oversimplified and it is rare to find aphasic patients with a pattern of deficit consistent with the functional roles the model ascribes to Broca's area, Wernicke's area, the angular gyrus and the arcuate fasciculus
• This might be because it is difficult to find patients where damage is confined to those regions alone, so symptoms will be a mixture of those associated with two or more types (mixture of Broca's, Wernicke's and Conduction)
• Wernicke-Geschwind model


  Model of language processing in the brain
• Studies over the last 30-40 years have revealed that Broca's area is, at best, only partly responsible for the functions originally ascribed to it by Broca and in the Wernicke-Geschwind model
• People with damage to Broca's area do not necessarily show the symptoms of Broca's aphasia
• Brain imaging studies have shown that the expected activity in Broca's area during word repetition is absent or much less than in other areas
• Broca's area (and/or nearby areas) are involved in comprehension of more complex grammatical structures than simple statements
• Broca's area plays a role in comprehension and perception, though the deficits associated with damage are quite mild
• When Broca's area tissue is removed surgically, the effects are much less pronounced than when the damage is due to a stroke in that area
• Recent neuroimaging results have implicated Broca's area in speech perception
• The damage affecting Broca's patients also affected the insula cortex, other deep white and grey matter structures and extended into the forebrain nuclei (including striatum and the globus pallidus)
• The functions ascribed to Broca's area seem to involve a number of regions in the vicinity of this area and not just this area
• The functional distinction between perception, comprehension and production does not appear to be mirrored in the brain: regions implicated in production may also be involved in comprehension and perception
• Contrary to the Wernicke-Geschwind model, visual information can reach Broca's area without going via the angular gyrus and Wernicke's area
• The Wernicke-Geschwind model represents a substantial oversimplification
• Damage to Wernicke's area alone produces rather mild symptoms
• The more severe symptoms associated with Wernicke's aphasia are not due to lesions of Wernicke's area itself, but to damage to neighboring regions
• Far more brain regions and structures are involved in language than are included in the Wernicke-Geschwind model
• Lichtheim model


  Extension to Wernicke's original model, proposed that interpretation of language required conceptual knowledge stored in a region outside the classic Broca and Wernicke areas
• Transcortical sensory aphasia symptoms have been observed, where patients are able to repeat what they have heard and to correct grammatical errors, but they are unable to understand what it means
• Transcortical motor aphasia symptoms have been observed, where patients have a tendency to obsessively repeat heard phrases (echolalia)
• Varieties of aphasia


  • Broca's Aphasia
  • Wernicke's Aphasia
  • Conduction Aphasia
  • Global Aphasia
  • Transcortical motor Aphasia
  • Transcortical sensory Aphasia