NEURAL SUBSTRATES OF MEMORY AND SEMANTIC PROCESSING

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The primary goal of this proposal is to provide further insight into the brain regions responsible for implicit and explicit memory in the verbal domain and lexical-semantic processing at the level of single words. The project will utilize a combined neuropsychological and event-related brain potential (ERP) approach to illuminate controversies surrounding the location and duration of repetition and semantic priming effects, the time course of memory encoding and retrieval, and the nature of conceptual memory stores (i.e., amodal or modality specific). Our previous studies suggested that both left and right inferior temporal- occipital regions are critical for visual word priming. Other results demonstrated that damage to inferior prefrontal cortex and adjacent regions produces significant impairments in lexical-semantic processing and reductions in the amplitude of ERPs observed in a lexical decision task. In the current proposal, we will study groups of patients with defined deficits in memory or language abilities. These patients have focal, MRI-confirmed lesions in subregions of (1) prefrontal cortex, (2) temporal-parietal junction, (3) inferior temporal-occipital extrastriate regions, or (4) hippocampal formation. Two sets of experiments are proposed: (1) Behavioral and ERP studies in controls and patients will systematically examine the neuroanatomical and neurophysiological substrates of implicit and explicit memory; (II) Behavioral and ERP studies of semantic priming for words and pictures will compare lexical and conceptual processing in patients with and without aphasia. This project will provide a wealth of data on the neuroanatomical and elecrophysiological substrates of memory and semantic processing, which are essential for a greater understanding of how these operations are affected by aging, psychiatric and neurodegenerative diseases, and neurological insults. The pattern of spared cognitive abilities in these patients is of great interest with future applications in the development of improved rehabilitation strategies.