Conduction aphasia Goodglass and his critics

Harold Goodglass in "Understanding Aphasia" (Academic Press, 1993) expresses the correlation with "afferent motor aphasia" (Luria) and central aphasia (Goldstein). The aphasia is fluent with consistent errors, especially phonemic paraphasias (tangling, transposing, substituting/insertion extra phonemes, stutterlike blocking). Errors may preferentially affect nouns/key words rather than grammatical forms, or resemble Wernicke's aphasia with syntactically disordered speech and attempts to repair syntax. Repetition is poor especially polysyllabic words. Auditory and even reading comprehension is relatively remarkably preserved. This feature differentiates from Wernicke's aphasia. Patients lack neologistic speech seen in Wernicke's aphasia and can correct errors offline (Shuren et al.). Mild cases may have paraphrase errors.

The anatomy may involve the supramarginal gyrus, compatible with Geschwind, or other lesions along the Sylvian fissure. Lesion extent is restricted though. K. Goldstein attributed central aphasia to an insular lesion (1948). Damasio and Damasio (1989) Neuroanatomy and Neuropsychological Disorders. Neuroimaging procedures and problmes, New York, Oxford Press) rejected disconnection, and attributed the disorder to a disruption of the perception and short term storage of phoneme strings and their assembly for production (blogger question: Did the Damasios give a hat tip to Luria???). They further stated the cortex and not the white matter had to be involved.

Nadeau reviews the anatomy of conduction aphasia and believes it to be partly reconciliable with the Wernicke-Geschwind model, with a center for auditory images in area 22 is linked to posterior inferior frontal lobe (Broca's area) via the arcuate fasciculus. Nadeau contends there is a two part language cortex, with one part extending from area 22 variably backwards into area 40, and that an anterior area extending variably from Broca's area to areas 4 and 6. There is substantial individual variability. fMRI and cortical stim studies (Ojemann and others) show distributed and hierarchical processes in 2 distributed systems but not necessarily disconnection.

There are white matter tracts between the two areas, and also WITHIN them. Acoustic representations within the STG (Howard et al, 1992, Brain 115: 1769-1782). The connectivity between the two areas could be direct or indirect, and be individually variable. Nadeau defines the anatomy of conduction aphasia as including, variably, the supramarginal gyrus, the posterior part of Wernicke's area, the angular gyrus and possibly the extreme capsule and insula. Nadeau thinks of it as a limited form of Wernicke's aphasia with better lexical access and more preserved acoustic hierarchy. He cites this as the view of Sigmund Freud.

Nadeau's views of PDP processing are elaborated extensively but omitted here.

Psycholinguistic accounts include Dubois et al. (1964) Etude neurolinguistique de l'aphasie de conduction. Neuropsychologia 2, 9-44. They noted worse repetition with longer sylables and witgh "negating prefixes" that confronted the speaker with a "high information decision at the end of the prefix" . In contrast, the anomic aphasics did well on negating prefixes but not with lexical selection. Pate et al (1987) Specifying the locus of impairment in conduction aphasia, Language and Cognitve processes 2:43-81, found identical pholonogical strings were harder to repeat if one word than if 2 words (murderous v. murder us). Geschwind noted difficulties with functor loaded sentences ("no if ands ands or buts") but Goodglass believes that is not reliable.

Warrington, Logue and Pratt (1972) Neuropsycologia 9:377-387 and Warrington and Shallice (1969) Brain 92:885-896 proposed decreased auditory short term memory as a feature of conduction aphasia (again the question: was there a hat tip to Luria for this "new" finding?). Their view was what Nadeau later called "repetition conduction aphasia." (see separate blog entry). That view was disputed by Strub and Gardner 1974 (Brain and Language) . Tzortzis and Albert (1974) and subsequent studies by Goodglass found "invariable" impaired auditory spans that is not adequate to explain the deficit; the persistent auditory trace allows attempts at self correction. The term "reproduction conduction aphasia" refers to the classical form of the disorder with problems beyond auditory memory impairment, encompassing equal impairments of oral reading and naming. Kohn (1984, Brain and Language) emphasized the phonlogical link between successive attempts and target words and considers the problem "post-lexical" ie. after achievement of phonological representation of the word, but before its motor realization, due to a breakdown of "prearticulatory programming" similar to Dubois.

Nadeau described 3 types of conduction aphasia from the literature. Please see separate entry regarding.