Neural activation patterns in chronic stroke patients with aphasia : the role of lesion site, lesion size and task difficulty

Functional 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 language functions in chronic phase for patients with different site and size of lesion when different tasks are used. The present study was aimed at exploring the role of perilesional, ipsilesional and contralesional regions in neural recovery in participants with aphasia with different site and size of lesion using three different language tasks. All patients in the present study were in the chronic stage who had achieved high levels of recovery. Functional magnetic resonance imaging (fMRI) was used to characterize cortical activation in eight stroke patients and eight age/gender matched controls during lexical decision, semantic judgment and picture naming. An event related design using jittered interstimulus intervals (ISIs) was employed to present the stimuli. The fMRI scans revealed differences in activation patterns across the three tasks. Normal control participants and participants with aphasia mainly activated the left perisylvian region during the lexical decision task and the semantic judgment task. However, during the picture naming task, all participants activated bilateral posterior regions irrespective of the site or size of lesion. Subsequent regions of interest analysis and laterality index analysis revealed that patients with larger lesions produced greater right hemisphere activation than patients with smaller lesions during the picture naming task. The results of this study demonstrate that recovery is task, lesion site and lesion size specific. Further, the findings of the present study indicate a role for both homologous contralesional cortex and perilesional and ipsilesional regions as efficient mechanisms for supporting language functions in chronic stroke patients.