Repeating with the right hemisphere: reduced interactions between phonological and lexical-semantic systems in crossed aphasia?

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.

Recovery from post-stroke aphasia: lessons from brain imaging and implications for rehabilitation and biological treatments.

Aphasia, a condition defined as the partial or complete loss of language function after brain damage, is one of the most devastating cognitive deficits produced by stroke lesions. Over the past decades, there have been great advances in the diagnosis and treatment of post-stroke language and communication deficits. In particular, the advent of functional brain imaging and other brain mapping methods has advanced our understanding of how the intact and lesioned brain takes over the activity of irretrievably damaged networks in aphasic patients. This review examines the contribution of these ancillary methods to elucidate the neural changes that take place to promote improvement of language function in early, late, and very late stages of recovery. Also, functional neuroimaging is helpful to identify brain areas involved in language recovery as well as to characterize the plastic reorganization of neural networks produced by scientifically-based language therapies and biological treatments (drugs, transcranial magnetic stimulation).