Role of the nondominant hemisphere and undamaged area during word repetition in poststroke aphasics - A PET activation study

Background and Purpose Although the resting regional cerebral blood flow (rCBF) in aphasic patients has been thoroughly investigated with positron emission tomography (PET) and single-photon emission CT, and PET studies in normal subjects have elucidated the functional localization of language processing, little is known about the activation pattern of language processing in aphasic patients. Methods We measured the changes in rCBF during a repetition task (hearing a single word and repeating it aloud) and the resting state using the (H2O)-O-15 PET activation technique in 6 normal subjects (mean+/-SD age, 58.3+/-8.1 years) and 16 aphasic patients: 10 fluent aphasics (age, 60.3+/-12.5 years) and 6 nonfluent aphasics (age, 50.5+/-8.3 years). Results In normal subjects, the posteroinferofrontal area (PIF) including Broca's area, the posterosuperotemporal area (PST) including Wernicke's area, the rolandic areas, and a few other areas were activated with left side dominance by the repetition task. In the resting state, the rCBF in the left PIF and the left posterotemporal area was reduced in both fluent and nonfluent aphasics. In aphasic patients, the magnitude of activation in the right PIF and PST by the repetition task was greater than in normal subjects. The increase in rCBF during the repetition task in the left PIF correlated with the Western Aphasia Battery score of spontaneous speech in the nonfluent aphasics with a left inferofrontal lesion. Conclusions This study shows the importance in aphasic patients of the mirror regions of the left PIF and PST in the nondominant (right) hemisphere for performing the word repetition task. The results also show the importance for nonfluent aphasic patients of the recruitment of the undamaged PIF for spontaneous speech.