Cerebral Localisation and Language Flashcards
Components of communication
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
Spectrogram
A photographic or other visual or electronic representation of a spectrum.
Speech perception theories
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
Vocalisation circuits
DIAGRAM
Auditory processing
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
How is auditory processing different to visual?
Representation of stimuli Sensitivity to temporal rather than spatial factors
Aphasia
Partial or complete language deficit
Broca’s discovery
Aphasic patient Tan had neurosyphilitic lesion in left hemisphere (on Broca’s area)
Wernicke’s discovery
Again localised to left hemisphere, but PRODUCTION, challenged Broca’s view that speech was localised to a single area –> a language network
The Wada procedure
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.
What does the Wada procedure support?
Supports the notion that speech is usually represented in the left hemisphere
Inactivation of left hemisphere inhibits both spoken and signed language
Modern view of the hemispheric localisation of speech
Left dominance is more generalized to communication-relevant information rather than words & speech per se
Global aphasia
Inability to understand language, speak or write
Broca’s (expressive) aphasia
This affects speech production and is associated with left hemisphere frontal lesions
Wernicke’s (receptive) aphasia
This affects comprehension and is mainly associated with lesions in Wernicke’s area of the left hemisphere
Flaws in the distinction between Broca’s and Wernicke’s aphasias?
Gross oversimplification
Broca’s aphasia
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)
Broca’s aphasia: Agrammatism
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.
Broca’s aphasia: Anomia and Articulation
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.
Insular cortex
100% overlap in insular lesions for patients with speech apraxia (deficit in motoric aspects of speech production)
Wernicke’s Aphasia
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.
Wernicke’s Aphasia symptoms
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 (theyre not deaf) so they will recognize a doorbell sound, bird singing, dog barking, etc. but they cannot understand speech.
Wernicke’s Aphasia: Word Deafness
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.
Wernicke’s Aphasia: Word Comprehension
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
Arcuate fasciculus
A direct connection between Wernicke’s and Broca’s enables patients with TSA to repeat words they cannot understand
Cause of TSA
Damage to the posterior language area; patient cannot understand the meanings of words but can repeat them
Sound and Word Repetition: Conductive Aphasia
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).
