Cerebral Localisation and Language

Question 1

Components of communication

Answer 1

Signal (what can be observed) –> channel (e.g. air) –> modified signal –> receiver
If receiver responds message can be deduced from observing behaviour
Repertoire deducible given observation of all signal-response pairs

Question 2

Spectrogram

Answer 2

A photographic or other visual or electronic representation of a spectrum.

Question 3

Speech perception theories

Answer 3

Auditory Theory: the continuous, varying auditory signal is matched to a finite
number of stored representations.
Motor Theory: auditory signal matched with internal speech motor program

Question 4

Vocalisation circuits

Answer 4

DIAGRAM

Question 5

Auditory processing

Answer 5

First cortical stage is primary auditory cortex (A1; Heschl’s Gyrus)
A1 of LH and RH both respond to speech sounds (Binder et al., 2000)
If these sounds are intelligible then LH temporal lobe becomes more active (Scott et al., 2000)
RH more responsive to melodic sounds

Question 6

How is auditory processing different to visual?

Answer 6

Representation of stimuli Sensitivity to temporal rather than spatial factors

Question 7

Aphasia

Answer 7

Partial or complete language deficit

Question 8

Broca’s discovery

Answer 8

Aphasic patient Tan had neurosyphilitic lesion in left hemisphere (on Broca’s area)

Question 9

Wernicke’s discovery

Answer 9

Again localised to left hemisphere, but PRODUCTION, challenged Broca’s view that speech was localised to a single area –> a language network

Question 10

The Wada procedure

Answer 10

The Wada procedure studies the function of a one hemisphere.
A fast-acting barbiturate (sodium amytal) is injected into the carotid artery on one side of the neck.
The drug effect is ipsilateral to the injected hemisphere - lasts about 10 minutes.
Limbs on the contralateral side are paralyzed and sensation is lost.
Asking the patient questions can assess his or her ability to speak.
If the injected hemisphere is dominant for speech the patient will be unable to talk until the anaesthetic wears off.

Question 11

What does the Wada procedure support?

Answer 11

Supports the notion that speech is usually represented in the left hemisphere
Inactivation of left hemisphere inhibits both spoken and signed language

Question 12

Modern view of the hemispheric localisation of speech

Answer 12

Left dominance is more generalized to communication-relevant information rather than words & speech per se

Question 13

Global aphasia

Answer 13

Inability to understand language, speak or write

Question 14

Broca’s (expressive) aphasia

Answer 14

This affects speech production and is associated with left hemisphere frontal lesions

Question 15

Wernicke’s (receptive) aphasia

Answer 15

This affects comprehension and is mainly associated with lesions in Wernicke’s area of the left hemisphere

Question 16

Flaws in the distinction between Broca’s and Wernicke’s aphasias?

Answer 16

Gross oversimplification

Question 17

Broca’s aphasia

Answer 17

Damage to Broca’s area disrupts the ability to speak. Broca’s patients:
Show slow, laborious speech; Have great difficulty saying function words (a, the, some, in,
about, etc.); But can produce content words (nouns, verbs, adjectives
and adverbs); Show some deficit in language comprehension (agrammatism); This is much more than a deficit in the motor sequencing for speech production (as attributed to Broca’s area by Wernicke)

Question 18

Broca’s aphasia: Agrammatism

Answer 18

Agrammatism: A deficit in using grammatical
constructions.
‘The horse kicks the cow’
Broca’s patients can understand sentences where the meaning is clear:
They have major problems when the meaning is not clear and you have to
rely on grammar for meaning.

Question 19

Broca’s aphasia: Anomia and Articulation

Answer 19

Anomia: A deficit in word ‘finding’; words are missed or inappropriately
substituted (a primary symptom of aphasia).
Articulation: A deficit in pronunciation, often altering the sequence of sounds.
Loci of damage: Articulation deficit is thought to be related to damage of
insular cortex.
Agrammatism and anomia are thought to be related to damage to inferior frontal lobes.

Question 20

Insular cortex

Answer 20

100% overlap in insular lesions for patients with speech apraxia (deficit in motoric aspects of speech production)

Question 21

Wernicke’s Aphasia

Answer 21

Damage to Wernicke’s area disrupts the comprehension of words and the production of meaningful speech.
Wernicke’s patients:
Show normal speech flow; no searching for words (Broca’s); Speech contains function words and appears grammatical; However, there are few content words; Extreme cases produce meaningless jumbles of words; Show poor comprehension (e.g., cannot point to ‘the object that contains ink’); Are apparently unaware of their deficit.

Question 22

Wernicke’s Aphasia symptoms

Answer 22

Wernicke’s symptoms can be grouped into three deficits:
recognition of spoken words
;comprehension of word meaning; ability to convert thoughts into words
Word Recognition: Contrasts to word comprehension. Recognition is perception.
Damage to left temporal lobe can produce a deficit in auditory word recognition – pure word deafness.
Patients can hear (they􏰄re not deaf) so they will recognize a doorbell sound, bird singing, dog barking, etc. but they cannot understand speech.

Question 23

Wernicke’s Aphasia: Word Deafness

Answer 23

Patients with word deafness:
have excellent speech; can understand speech by lip reading (so comprehend OK); can communicate by writing.
Two types of brain injury cause word deafness:
disruption of auditory input to Wernicke’s area; disruption of Wernicke’s area itself.

Question 24

Wernicke’s Aphasia: Word Comprehension

Answer 24

Word Comprehension: failure to comprehend the meaning of words
and an inability to express thoughts in meaningful speech.
Damage to the posterior language area (that spares Wernicke’s area) causes transcortical sensory aphasia (TSA).
Patients with TSA: can repeat words spoken by others; don’t understand the meaning of words they hear and repeat; can’t produce their own meaningful speech
So comprehension and recognition are carried out by different areas.
Wernicke’s aphasia = word deafness + transcortical sensory aphasia

Question 25

Arcuate fasciculus

Answer 25

A direct connection between Wernicke’s and Broca’s enables patients with TSA to repeat words they cannot understand

Question 26

Cause of TSA

Answer 26

Damage to the posterior language area; patient cannot understand the meanings of words but can repeat them

Question 27

Sound and Word Repetition: Conductive Aphasia

Answer 27

Patients with TSA: can repeat words that they hear; have intact Wernicke’s and Broca’s areas.
The arcuate fasciculus connects Wernicke’s and Broca’s areas. This axon bundle appears to convey information about the sounds of words but not their meanings. The arcuate fasciculus is damaged in conduction aphasia.
Patients with conduction aphasia can repeat speech sounds only if these sounds have meaning (i.e., make a real word known to them).