| Sumario: | Many parts of the brain are responsible for different aspects of memory functioning; however, researchers disagree over whether memory consists of a single system or several interrelated systems. To differentiate theories of explicit and implicit memory, provide convergent validation for imaging studies, replicate and extend Dillon (1996, unpublished master's thesis), and better understand processes involved in rehabilitation of stroke patients, 20 stroke patients with discrete brain lesions and 20 controls were tested with explicit (awareness of having learned) and implicit (priming) memory tasks in both auditory and visual modalities. Stroke patients were divided into anterior versus posterior and left versus right groups based on location of cortical and subcortical lesions. The current study did not consistently agree with findings from imaging studies done with neurologically normal subjects. Whereas brain imaging studies generally found increased activation in anterior and hippocampal brain structures during performance of explicit memory tasks and decreased activation in posterior brain structures during performance of implicit memory tasks, all subjects but those in the left posterior brain lesion group were impaired on explicit recall relative to normal controls, and all patient groups demonstrated preserved implicit priming. This study did replicate the unusual finding from Dillon (1996) that altering modality conditions affected explicit memory performance. Within-modality performance was greater than cross-modality performance in normal controls for explicit but not for implicit memory performance. Lesion location did influence modality effects. Anterior lesions impaired cross-modality recall, whereas posterior lesions impaired within-modality recall. Modality of presentation was determined to be an important consideration in rehabilitation. The idea that there is a single memory system was not supported by this study. Data are more consistent with the ideas that items to be remembered are located in multiple cortical and subcortical regions of the brain and that there are separate systems or pathways for explicit or implicit access to these items. Thus, lesions of multiple areas of the brain produce similar memory deficits.
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