Right hemisphere activation in recovery from aphasia -: Lesion effect or function recruitment?

Background: Some neuroimaging studies have suggested that specific right hemispheric regions can compensate deficits induced by left hemispheric lesions in vascular aphasia. In particular, the right inferior frontal cortex might take part in lexical retrieval in patients presenting left-sided lesions involving the homologous area. Objective: To address whether the involvement of the right inferior frontal cortex is either unique to recovering aphasic patients or present also in other circumstances of enrichment of lexical abilities, i.e., in non-brain-damaged subjects over learning of new vocabulary. Methods: Ten post-stroke aphasic patients experiencing word finding difficulties were intensively trained to retrieve object names in French over a 4-week period. Twenty healthy subjects were similarly trained to name these items in either Spanish or English, i.e., foreign languages that they learned at school but did not master. By analogy to aphasic patients, healthy subjects had to work out the phonetic/phonologic representations of long-acquired but forgotten words. Brain activity changes were assessed in two H-2 O-15 PET sessions involving picture naming tasks that were performed before and after training. Results: Comparable post-training performance and changes in regional cerebral blood flow including mainly the right insular and inferior frontal regions were found in both groups. Conclusion: Our results suggest that enhanced activities in right-sided areas observed in recovering aphasia is not the mere consequence of damage to left-sided homologous areas and could reflect the neural correlates of lexical learning also observed in control subjects.