Semantic memory refers to our store of knowledge about the world and about the meaning of words, which we use in countless everyday tasks such as recognizing objects, communicating, and making decisions. Functional imaging research and studies of patients with brain damage show that much of the temporal lobe in the human brain is devoted to storing semantic memory. Despite a wealth of such research, the basic organization of the semantic memory store is not yet understood. The proposed research uses functional magnetic resonance imaging to address four major questions that are central to defining the neurobiology of this system. The first question is whether the temporal lobes store concept nformation in different locations based on either the category of the concept (e.g., animal, plant, artifact) or the perceptual modalities by which the concept is usually experienced (e.g., vision, audition, motor manipulation). The second question concerns how the semantic memory system stores """"""""encyclopedic"""""""" information learned purely through language rather than direct perceptual experience. Despite the importance of such knowledge in everyday life, almost no physiological research on this topic has been conducted. The third question addresses how the brain combines concepts to produce more complex meanings, as happens whenever two content words are used together in a phrase or sentence. Proposed studies will test the hypothesis that much of this conceptual combination happens quickly and automatically within the semantic memory system. This process is ubiquitous in language and thought but has received little attention among neurobiologists. The final question concerns the role of the right, non-dominant hemisphere in semantic memory. Proposed studies will test the hypothesis that the right hemisphere activates a broader network of semantic relationships and alternative meanings than the left hemisphere, allowing it to contribute to the interpretation of ambiguous words and figurative language. Relevance: The issues addressed in this research are central to our understanding of how the brain processes conceptual knowledge. This work will have critical implications for several common brain illnesses that affect the temporal lobes and feature impairments in conceptual processing, including Alzheimer's disease and related dementias, stroke with fluent aphasia, temporal lobe epilepsy, and schizophrenia.
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