Role of the Right Brain in Recovery of Language Function in Chronic Stroke

Background: Aphasia, a language impairment usually induced by stroke, is typically the result of damage to the left hemisphere. Severity of this disorder can vary across patients, as well as the degree of impairment at various levels of linguistic processes. However, one consistent symptom of aphasia is anomia (or dysnomia) which is a word finding deficit. Given the reliable presence of anomia, picture naming is a common task used both clinically and experimentally to probe linguistic processing. Functional imaging studies have suggested that the right hemisphere may be recruited to compensate for loss of left hemispheric language regions. However, they could not assess the functional significance of the observed activations. In a previous experiment (NIDCD protocol 92-DC-0178), we have identified the areas activated in association with language function (picture naming) in patients with chronic stroke that have partially recovered from an initially severe aphasia and in healthy, age- and gender-matched controls. The preliminary outcome is increased involvement of the right hemisphere for picture naming in recovered aphasics. Objectives: In the present protocol, we plan to test the hypothesis that right hemispheric homologues of traditional left hemispheric anterior and posterior language areas are the neural substrate mediating recovery of language functions in patients with chronic stroke. This investigation is important because it can provide novel evidence on plasticity of language functions in chronic stroke. Study Population: We plan to include chronic stroke patients that suffer from aphasia, and healthy, age- and gender-matched controls. Design: We will test if inhibitory transcranial magnetic stimulation (TMS) of right-hemispheric cortical areas (inferior frontal gyrus - IFG, superior temporal gyrus - STG, middle temporal gyrus - MTG) that are activated during picture naming will result in a decrease in task performance (picture naming latency) in chronic stroke patients, in comparison to stimulation of left hemispheric areas in aphasics, and right-hemispheric homologue areas in healthy controls. The TMS experiment is necessary to identify a cause-effect link between right hemispheric activation and recovery of language functions after chronic stroke. Stereotactic applications of TMS during the picture naming task will be implemented over six cortical sites in both groups: left IFG, left STG, left MTG, and right IFG, right STG, and right MTG. Outcome Measures: The outcome measure will be performance on the picture naming task (primary outcome measure reaction time) during TMS as a function of subject group and stimulation site.