F MRI STUDY OF TASTE CORTEX USING FOCAL STIMULI

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The short term goals of this proposal are to determine whether the location of cortical taste processing in humans depends on the location of the taste stimulus on the tongue. We will construct and test a taste stimulator for applying chemical taste stimuli to discrete parts of the tongue and observe the resulting central activation with functional magnetic resonance imaging (fMRI). We hypothesize that taste processing in the primary gustatory cortex as well as in some second or higher order cortical taste areas will be mostly in the right hemisphere in right handed subjects regardless of the side of the tongue that was stimulated. We also hypothesize that taste information from the vallate papillae on the posterior tongue will be processed in a different part of the primary gustatory cortex than that from the fungiform papillae on the anterior tongue. Long term goals include the comparison of left and right handed subjects, and examination of responses to stimulation of other taste bud fields. A long term objective is to understand the nature and limitations of the biological response to peripheral damage to the taste system. The peripheral part of the human taste system includes 5 distinct fields of taste buds, innervated by at least 4 branches of 3 cranial nerves. Thus loss of taste function resulting from peripheral lesions or disease is rarely complete. For example, one of the taste nerves, the chorda tympani, is often damaged during oral surgery, middle ear surgery, or from disease (e.g. Bell's Palsy). The remaining intact taste buds and their innervating nerve fibers can often mediate relatively normal perception. Central compensatory mechanisms may be partially responsible for this recovery. A necessary step for revealing such compensatory mechanisms is to establish normal patterns of central activation resulting from selective stimulation of the individual fields of taste buds.