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Abstract Dysphasia, 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 dysphasic patients. Right hemisphere (RH) regions contralateral to the dysphasiainducing lesion may be recruited to support recovery of language. Several variables affect language recovery–related neuroplastic processes, including patient variables. Patients vary with regard to lesion characteristics and the language deficits that they present. Lesions may extend beyond their structural boundaries, and we therefore recommend using perfusion imaging as well as structural imaging to determine the dimensions of the lesion and, in turn, to determine candidate tissue for recovery. Because it is possible that damage to white matter connections may play a role in dysphasia recovery, we recommend that future studies of language recovery use diffusion tensor imaging to evaluate the integrity of these pathways. Dysphasia following a right hemisphere lesion (crossed dysphasia) in right-handed individuals is rare, most studies shows a prevalence of less than 3%. Two studies reported an increased incidence of about 20% to 25% for language deficits in left- or non-right-handers after right hemispheric stroke. Another study found no such increase and suggested a negligible role of the right hemisphere in speech function in most leftSummary and Conclusions 128 handers without a history of early left-hemisphere damage. Only 38% of hemispheric lesions in the language dominant hemisphere will result in transient, and 18% in permanent dysphasia. Difficulties in the assessment of language performance due to physical exhaustion and deficits in attention in the early stages after stroke and restitution in the later stages may have led to an under diagnosis of dysphasia in right-hemispheric stroke patients. Another shortcoming of studies on differences in dysphasia incidences in left- and right-handers is the small number of lifthanders with right-hemispheric stroke and dysphasia. Additionally, patients with language disturbances after cerebral infraction do not infrequently have pre-existing lesions in the other hemisphere rendering conjectures on the original hemispheric language dominance ambiguous. In addition, patients with crossed dysphasia often have subcortical lesions instead of lesions of classical language areas. Previous research data suggest that the right hemisphere participate in language recovery and treatment gains in dysphasia. In cases of large lesions and poorer recovery, right-hemisphere activity is prominent. The fact that recovery in these cases is poor does not indicate that the right hemisphere is not useful for or necessarily interferes with language processes. Rather, it suggests that right-hemisphere structures are most active when left-hemisphere structures are so damaged that they are not adequate for the task. It is possible that activity in both hemispheres of dysphasia patients interferes with language processes, depending on the patient, the size of the lesion, and the severity of dysphasia. Evidence suggests that silencing such extraneous activity in either hemisphere will have a positive impact on treatment. Previous findings suggest that lateralization of brain processes related to language is not entirely a passive process, but can be influenced Summary and Conclusions 129 by manipulation of attention. Initial findings indicate that pairing an intention manipulation (complex left-hand movement) with picture naming during treatment has a positive impact on outcome and shifts lateral frontal activity toward the right hemisphere. However, these data, especially the fMRI data, should be considered preliminary at this point in time. Much work has to be done before the full impact of this manipulation on treatment can be assessed. For example, it is unknown how much the complex left-hand movement contributes to treatment outcome and re-lateralization of lateral frontal activity to the right hemisphere. Several studies are currently conducting a study to address these questions. Another question that should be addressed is whether the intention manipulation can enhance the effects of other treatment manipulations. Hence, there is much work to be done before we completely understand the potential contributions of the intention component to treatment outcome. At the beginning of this essay, I noted that two simple, related assumptions regarding the development of new treatments for dysphasia. The first was that dysphasia researchers and clinicians can develop treatments to engage specific neural substrates in the service of dysphasia rehabilitation. Implementing this conceptually driven method requires that was learn a great deal more than currently know about the neural substrates of treatment and recovery of function in dysphasia. Doing so will require increasing investment in functional imaging studies. The second, related assumption was that dysphasia researchers can use functional brain imaging to ascertain whether treatments developed in this fashion actually engage the targeted substrates. The findings regarding to the novel intention treatment are promising in this regard. Summary and Conclusions 130 This treatment was developed to help patients with nonfluent dysphasia focus word production mechanisms in the right lateral frontal lobe. CONCLUSION To date, functional imaging data suggest that all studies and researches have been successful in accomplishing this goal. More importantly, the data suggest that fMRI and other functional imaging modalities can be a powerful tool in developing conceptually driven treatments for dysphasia that target specific neuroplastic substrates. Findings from functional imaging can be used to verify the conceptual basis of the treatment and to guide further development |