Studies of normal subjects and neurological patients show that the integrity of the left inferior and polar temporal cortex is critical to normal lexical-semantic processes, and that the anatomic substrates of these processes are partially segregated by conceptual category. We will probe the role of these regions in lexical processing using two empirical effects (the semantic interference and word frequency effects) that arise from differential demands on lexical selection and phonological code activation, respectively. The physiologic correlates of these effects, measured with functional magnetic resonance imaging (fMRI), will illuminate the role of the left extrasylvian temporal lobe in normal lexical processing, and clarify whether neural regions specifically involved in lexical processing are segregated by conceptual category. Finally, we will take advantage of a unique Patient Registry including subjects with acquired left temporal lobe damage and anomia. We will examine the correlates of the semantic interference and word frequency effects in these subjects using fMRI techniques that isolate the correlates of successful naming trials. The results will clarify the neural basis for residual lexical retrieval after damage to preferred neural systems. The studies undertaken here address wider issues of plasticity, recovery, and the interplay of systems related to language and memory, and will promote adaptation of fMRI imaging technology to language-impaired patients, in whom it may be used to track the course of disease and recovery, as well as responses to treatment.
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