Neural basis of language

Question 1

What are the symptoms of Broca’s aphasia?

Answer 1

1. Speech is slow and laboured
2. Patients are able to communicate using selection of nouns
3. Use of verbs and other grammatical devices is poor/absent
4. Patients are unable to repeat sentences
5. Patients have no impairment in understanding speech

Question 2

What is the location of Broca’s area?

Answer 2

• Left posterior-inferior frontal lobe
• Brodmann’s areas 44 & 45

Question 3

What is the nature of comprehension deficit in Broca’s aphasia?

Answer 3

• Patients are able to understand sentences when the meanings of the sentences are dependent on the meaning of words in sentence.
• When meaning of sentence is dependent on grammatical structure, patients have more difficulty.

Question 4

What are the symptoms of Wernicke’s aphasia?

Answer 4

1. Speech is normal speed and effortless
2. Contents of patient’s speech is often unintelligible because:
   - Use of wrong/non-existent words
   - Confusion of phonemes
3. Patients have impaired understanding of speech

Question 5

What is the location of Wernicke’s area?

Answer 5

• Left superior temporal lobe
• Brodmann’s area 22
• Posterior sector of left auditoy association cortex

Question 6

Which hemisphere is dominant in language processing?

Answer 6

Left hemisphere

Question 7

What is the Wada procedure?

Answer 7

• Subjects were divided into groups based on whether they were left or right-handed.
• Short-acting anaesthetic is injected into the right/left carotid artery and caused transient paralysis of ipsilateral hemisphere.
• Subjects were then assessed on their speech capability.
• Speech impairment implied representation of speech in associated hemisphere.

Question 8

What is the function of the non-dominant hemisphere in language processing?

Answer 8

Prosody (emotional and tonal colouring of speech)

Question 9

What evidence is there to support the function of the non-dominant hemisphere?

Answer 9

1. Posterior right hemisphere damage causes difficulty in interpreting emotions in speech.
2. Anterior right hemisphere damage causes inappropriate intonations in speech.

Question 10

What are the symptoms of conduction aphasia?

Answer 10

1. Unimpaired comprehension of speech
2. Unimpaired speech production
3. Impaired repetition of sentences

Question 11

What are the causes of conduction aphasia?

Answer 11

Damage to the arcuate fasciculus in domaint hemisphere

Question 12

What are the symptoms of transcortical sensory aphasia (TSA)?

Answer 12

1. Impaired comprehension of speech
2. Unimpaired speech production
3. Speech is unintelligible
4. Unimpaired ability to repeat sentences

Question 13

What are the causes of TSA?

Answer 13

Damage to temporal lobe surrounding Wernicke’s area in dominant hemisphere

Question 14

What are the symptoms of transcortical motor aphasia (TMA)?

Answer 14

1. Speech is slow and laboured
2. Patients are able to communicate using selection of nouns
3. Use of verbs and other grammatical devices is poor/absent
4. Unimpaired ability to repeat sentences

Question 15

What are the causes of TMA?

Answer 15

Damage to anterior superior aspects of frontal lobe in dominant hemisphere

Question 16

What is the pathway for spoken word processing in Wernicke-Greschwind model?

Answer 16

1. Auditory information processed in primary auditory cortex.
2. Information passed to Wernicke’s area where comprehension (at least partly) occurs (i.e. how the different sounds translate to words).
3. Information then passed to higher association areas where the semantic elements of speech are decoded (i.e. what the different words mean).

Question 17

What is the pathway for written word processing in Wernicke-Greschwind model?

Answer 17

1. Visual information is processed in the primary visual cortex.
2. Information passed to the angular gyrus where it is converted into an ‘internal monologue’, or speech representation.
3. ‘Internal monologue’ processed by Wernicke’s area like spoken word.
4. Information then passed to higher association areas where semantics are processed.

Question 18

What are the limitations of the Wernicke-Greschwind model?

Answer 18

1. When reading, information from visual cortex does not pass through angular gyrus or Wernicke’s area. This was found when reading words only activated visual cortex and not Wernicke’s area of angular gyrus in fMRI studies.
2. Speech comprehension is not a distinct process from speech production.
3. Specific anomias and other language deficits imply that specch comprehension may not be mediated by one area of the brain (i.e. Wernicke’s area).
4. No inclusion of subcortical areas involved in language (e.g. basal ganglia).

Question 19

What is the pathway for speech processing in Wernicke-Greschwind model?

Answer 19

1. High association areas generate the semantics that need to be expressed.
2. Both Broca’s area and Wernicke’s area are involved in converting semantics into works and ordering the words into coherent sentences.
3. Motor and premotor areas then convert words into series of appropriate muscle movements of mouth and tongue for articulation.