Neurobiology of learning, memory and cognition: Neural basis of language Flashcards
Aphasias
Disorders of language, often in the absence of additional cognitive impairment or inability to move the muscles used in speech.
Hemispheric specialisation
Split brain patients
WADA proceedure
Language deficits associated primarily with damage to left hemisphere.
Split brain patients: had corpus callosum & anterior commissure severed. NB somatosensory information from right hand processed by left somatosensory cortex & vv)
- object in right hand named appropriately
- object in left hand could not be named- only indirect description relying on rudimentary words.
Using WADA procedure: 96% right handers showed speech representation on the left (0 bilateral). 70% left handers showed speech representation on the left (15% bilateral, 15% on right)
Subsequently shown that left hemisphere can respond to written commands, right responds primarily to non-verbal stimuli.
Broca’s aphasia
Site of damage: motor association cortex of frontal lobe
Good comprehension.
Speech is nonfluent, agrammatical
Repetition impaired, paraphasic errors
Wernicke’s aphasia
Site of damage: posterior temporal lobe
Poor comprehension
Speech is fluent, grammatical, meaningless
Impaired repetition, paraphasic errors
Wernicke’s original model
Proposed that the two different aspects of language processing (comprehension & production) were associated by fibre tracts- arcuate fasciculus.
Predicted the existence of conduction aphasics, where damage to the fibre tracts would produce impairment in repetition of the spoken word, in the absence of deficits in spontaneous speech or word comprehension.
WADA procedure
Short acting anaesthetic, e.g sodium amytal, injected into left or right carotid artery -> thus anesthetising the ipsilateral hemisphere.
Patient is asked questions to assess ability to speak.
Lichtheim’s model (extended Wernicke’s)
Suggested that TMA and TSA were due to disconnection of language centres from ‘concept’ centres.
Conduction aphasia
Site of damage: arcuate fasiculus
Good comprehension
Speech is fluent, grammatical
Impaired repetition, paraphasic errors.
Global aphasia
Site of damage: portions of temporal & frontal lobes
Poor comprehension
V little speech
Impaired repetition
Transcortical motor area aphasia (TMA)
Site of damage: frontal lobe anterior to Broca’s
Good comprehension
Speech is nonfluent, agrammatical
Repetition not impaired (can repeat even very long sentances), paraphasic errors
Transcortical sensory aphasia (TSA)
Site of damage: cortex near junction of temporal, parietal & occipital lobes
Poor comprehension
Speech is fluent, grammatical, meaningless
Repetition not impaired, paraphasic errors
Can even make grammatical corrections to a sentance they don’t understand.
Anomic aphasia
Site of damage: Inferior temporal lobe
Comprehension good
Speech is fluent, grammatical
Repetition not impaired, no paraphasic errors.
Wernicke-Geschwind model 1960s
Extended Lichtheims.
Suggested distinct routes for written & spoken word
Spoken word -> area 41, 42 (auditory cortex) -> Wernicke -> hear & comprehend word
Cognition -> Wernicke -> Broca -> Face -> Cranial nerves -> speak
Written word -> Area 17 (visual cortex) -> Area 18,19 (visual cortex) -> Area 39 (angular gyrus) -> Wernicke -> read.
Thus, ultimately written word had to be converted into some kind of auditory format.
NB PROBLEMS.
Role of the right brain in language
Imp in the emotional & tonal colouring of language- prosody.
Patients with anterior right hemisphere damage produce inappropriate intonation in speech.
Patients with posterior right hemisphere damage have difficulty interpreting emotion in others speech.
NB importance to functioning in social settings.
Prosody
The emotional and tonal colouring of language
