Task-modulated neural activation patterns in chronic stroke patients with aphasia

Background: Neuroimaging research on language recovery in patients with aphasia due to left hemisphere damage has generated some intriguing results. However, it is still not clear what role the right hemisphere plays in supporting recovered language functions in the chronic phase for patients with different site and size of lesion when different tasks are used. Aims: The present study aimed at exploring the role of perilesional, ipsilesional, and contralesional activation in participants with aphasia with different site and size of lesion using two different language tasks. All participants were in the chronic stage with wellrecovered or significant improvements in language functions. Methods & Procedures: Functionalmagnetic resonance imaging (fMRI) was used to characterise brain activations in eight stroke patients and eight age/gender-matched controls during semantic judgement and oral picture naming. An event-related design using jittered interstimulus intervals (ISIs) was employed to present the stimuli. Outcomes & Results: The fMRI scans of both language tasks in patients revealed differences in activation pattern relative to the normal control participants. The nature of this difference was task specific. During the semantic judgement task patients without lesions involving the left frontal region activated the left inferior frontal gyrus similar to observations in the normal control participants. Participants with left frontal lesions activated contralesional regions in addition to perilesional left frontal regions. During the picture-naming task all participants activated bilateral brain regions irrespective of the site or size of lesion, consistent with other published studies utilising this task. Subsequent regions of interest analysis and laterality index analysis revealed that patients with large lesions produced greater right hemisphere activation than patients with small lesions. Conclusions: The results of this study demonstrate that recovery is task, lesion site, and size specific. Further, the results also indicate a role for both activation of homologous contralesional cortex and activity of left hemisphere regions (perilesional and ipsilesional) as efficient mechanisms for supporting language functions in chronic stroke patients.