Memory impairment associated with stroke and aphasia.

Abstract

Brain structures in the perisylvian region that are critical for language also subserve verbal memory processes. Researchers have documented a reduction in verbal memory span in individuals with perisylvian stroke resulting in aphasia, but scant data are available regarding the integrity of long-term memory in such individuals. Whereas dissociated memory processes have been documented in nonaphasic populations, characteristic patterns of short- versus long-term memory have not typically been associated with specific lesion sites in aphasic individuals. The purpose of this study was to examine memory abilities of aphasic individuals in relation to site of neurological lesion resulting from cerebrovascular accident. Fourteen individuals with stroke and aphasia and fourteen demographically matched control subjects were given selected tests of short-term memory (STM) and long-term memory (LTM). The stroke patients represented two distinct groups with regard to site of neurological lesion: seven with anterior lesions, seven with posterior lesions. STM was assessed with Digits Forward and Tapping Forward subtests from the Wechsler Memory Scale-Revised (Wechsler, 1988). Verbal LTM was assessed using two multitrial free recall paradigms. One paradigm required free recall of a word list presented aurally with selective reminding of unrecalled items. The other required free and cued recall of a word list presented with guided semantic encoding. Stroke patients were impaired relative to normal control subjects on tests of verbal memory, with greater impairment of LTM associated with anterior lesions and greater impairment of STM associated with posterior lesions. Individuals with anterior lesions were deficient in the enactment of successful LTM encoding and retrieval strategies. The posterior aphasia group was most impaired for digit span, a task dependent upon subvocal rehearsal. There were no group differences on a test of visual short-term memory. Verbal memory performance did not correlate highly with language ability, and did not appear to be simply a consequence of language impairment. The memory impairments observed in aphasic stroke patients were interpreted as working memory impairments with distinct manifestations dependent upon lesion site.