Conduction aphasia
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Conduction aphasia, also called associative aphasia, is an uncommon form of difficulty in speaking (aphasia). It is caused by damage to the parietal lobe of the brain. An acquired language disorder, it is characterised by intact auditory comprehension, coherent (yet paraphasic) speech production, but poor speech repetition. Affected people are fully capable of understanding what they are hearing, but fail to encode phonological information for production. This deficit is load-sensitive as the person shows significant difficulty repeating phrases, particularly as the phrases increase in length and complexity and as they stumble over words they are attempting to pronounce.[1][2] People have frequent errors during spontaneous speech, such as substituting or transposing sounds. They are also aware of their errors and will show significant difficulty correcting them.[3]
Conduction aphasia | |
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Other names | Associative aphasia |
Broca's area and Wernicke's area of the brain, which are also terms for different types of aphasia | |
Specialty | Neurology |
For example:
Clinician: Now, I want you to say some words after me. Say 'boy'.
Aphasic: Boy.
Clinician: Home.
Aphasic: Home.
Clinician: Seventy-nine.
Aphasic: Ninety-seven. No ... sevinty-sine ... siventy-nice...
Clinician: Let's try another one. Say 'refrigerator'.
Aphasic: Frigilator ... no? how about ... frerigilator ... no frigaliterlater ... aahh! It's all mixed up![4]
In 1970, Tim Shallice and Elizabeth Warrington were able to differentiate two variants of this constellation: the reproduction and the repetition type. These authors suggested an exclusive deficit of auditory-verbal short-term memory in repetition conduction aphasia whereas the other variant was assumed to reflect disrupted phonological encoding mechanism, affecting confrontation tasks such as repetition, reading and naming in a similar manner.[5]
Left-hemisphere damage involving auditory regions often result in speech deficits. Lesions in this area that damage the sensorimotor dorsal stream suggest that the sensory system aid in motor speech. Studies have suggested that conduction aphasia is a result of damage specifically to the left superior temporal gyrus and/or the left supra marginal gyrus.[6] The classical explanation for conduction aphasia is a disconnection between the brain areas responsible for speech comprehension (Wernicke's area) and that of speech production (Broca's area). This is due to specific damage to the arcuate fasciculus, a deep white matter tract. Aphasic people are still able to comprehend speech as the lesion does not disrupt the ventral stream pathway.