ABSTRACT
There is substantial evidence that individuals with language impairments resulting from brain damage, such as stroke-induced aphasia, show recovery of language function despite sustained damage to left perisylvian language areas (1). A long-held view is that language recovery following left hemisphere injury depends on right hemisphere mechanisms. Lesion studies support this claim, i.e., language recovers to some degree in individuals with large left hemisphere lesions (2,3), and patients with left hemisphere lesions show disruption of residual language after transient anesthesia of the right hemisphere with sodium amobarbital (4). Further, patients, who show recovery following left hemisphere lesions, show deterioration of language after a second lesion in the right hemisphere (5). Studies of language development and restitution in left-hemispherectomized individuals also provide compelling evidence that the right hemisphere has the capacity to subserve language (6,7). However, there also is clinical evidence that recovery of function involves expanded cortical language regions in the left hemisphere (8). For example, individuals with aphasia often show further language decline following a second stroke in the left hemisphere (2), suggesting that cortical regions in the left hemisphere are recruited into the language network when brain damage occurs. Findings from lesion studies, thus, indicate that the primary neural mechanisms instantiated to sustain language recovery include areas in the right hemisphere, and=or spared brain tissue in the damaged (usually left) cerebral hemisphere. More recently, neuroimaging studies
examining the mechanisms underlying recovery of language in aphasia have been reported with evidence largely supporting these patterns, but providing additional detail regarding the tissue recruited in recovery and highlighting variability in recovery patterns. In this chapter, neuroimaging studies of brain-damaged individuals are reviewed and factors related to neuroplastic processes in aphasia are discussed.
