Cortical activation studies in aphasia.

Positron emission tomography and functional magnetic resonance imaging are the major techniques of functional brain imaging. Both techniques have been used successfully in studies of the speech-relevant cortex in normal individuals and in aphasic patients with brain lesions. The activation studies basically agree with the classic model of language organization in that the left inferior frontal and superior temporal cortex (Broca's and Wernicke's area, respectively) are the pivotal areas of speech processing. Activation studies additionally emphasize that the speech-relevant cortex is a rather widespread network. It also encompasses contributions from other left hemispheric regions and, to some degree, from the contralateral right hemisphere. The studies of aphasic patients point out that the functional preponderance of the left over the right cerebral hemisphere varies between individuals, and that language recovery after stroke depends on the restitution of the speech-relevant network in both brain hemispheres.