Abstract
Knowledge on the patterns of repetition amongst individuals who develop language deficits in association with right hemisphere lesions (crossed aphasia) is very limited. Available data indicate that repetition in some crossed aphasics experiencing phonological processing deficits is not heavily influenced by lexical-semantic variables (lexicality, imageability, and frequency) as is regularly reported in phonologically-impaired cases with left hemisphere damage. Moreover, in view of the fact that crossed aphasia is rare, information on the role of right cortical areas and white matter tracts underpinning language repetition deficits is scarce. In this study, repetition performance was assessed in two patients with crossed conduction aphasia and striatal/capsular vascular lesions encompassing the right arcuate fasciculus (AF) and inferior frontal-occipital fasciculus (IFOF), the temporal stem and the white matter underneath the supramarginal gyrus. Both patients showed lexicality effects repeating better words than non-words, but manipulation of other lexical-semantic variables exerted less influence on repetition performance. Imageability and frequency effects, production of meaning-based paraphrases during sentence repetition, or better performance on repeating novel sentences than overlearned clichés were hardly ever observed in these two patients. In one patient, diffusion tensor imaging disclosed damage to the right long direct segment of the AF and IFOF with relative sparing of the anterior indirect and posterior segments of the AF, together with fully developed left perisylvian white matter pathways. These findings suggest that striatal/capsular lesions extending into the right AF and IFOF in some individuals with right hemisphere language dominance are associated with atypical repetition patterns which might reflect reduced interactions between phonological and lexical-semantic processes.
Highlights
It is well-established that the majority (95%) of right-handers have their left cerebral hemispheres dominant for language (Annett, 1998; Wada and Rasmussen, 2007)
Diffusion tensor imaging disclosed damage to the right long direct segment of the arcuate fasciculus (AF) and inferior frontal-occipital fasciculus (IFOF) with relative sparing of the anterior indirect and posterior segments of the AF, together with fully developed left perisylvian white matter pathways. These findings suggest that striatal/capsular lesions extending into the right AF and IFOF in some individuals with right hemisphere language dominance are associated with atypical repetition patterns which might reflect reduced interactions between phonological and lexical-semantic processes
The syndrome that best fits with the one we found in JAM and AFL after right hemisphere injury is characterized by poor comprehension, fluent Wernicke’s type speech, and lasting right hemiplegia in association with left capsular/putaminal damage and posterior lesion extension to the auditory radiations in the temporal stem (Cases 4, 5, and 6 in Naeser et al, 1982, pp. 8–10)
Summary
It is well-established that the majority (95%) of right-handers have their left cerebral hemispheres dominant for language (Annett, 1998; Wada and Rasmussen, 2007). Crossed aphasia is rare, analysis of language functioning in these subjects represents an ideal opportunity to examine whether their language performance and neural architecture underpinning language functions in the right hemisphere are the same as those reported in subjects with left hemisphere language dominance (Catani et al, 2007; Turken and Dronkers, 2011; Catani and Thiebaut de Schotten, 2012). We report the occurrence of fluent aphasia with severely abnormal repetition and deficits in sentence comprehension (conduction aphasia, CA) in two patients who suffered large right subcortical stroke lesions. This clinical-anatomical correlation is uncommon, but its description can further illuminate the neural organization of propositional language in the right hemisphere. In an attempt to accomplish this, in the present study the localization of damage to white matter tracts underpinning
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