Oral Somesthesis and Taste

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The long-term goal of this project is to understand how the somesthetic and gustatory systems function together to produce oral sensations and flavors This goal will be pursued by taking advantage of three recent psychophysical findings that provide novel insights into how somatosensory stimulation can influence taste. First, studies will be conducted to investigate the phenomenon of thermal taste, in which tastes can be induced by temperature alone. Of particular interest are sources of individual and spatial variation in thermal taste, interactions between thermal taste and chemical taste, and the spatial and temporal characteristics of thermal tastes as they relate to the sensitivity to warmth and cold. Second, the induction and perception of 'phantom' tastes caused by brief bouts of cold stimulation on the front of the tongue will be investigated. These cold-induced phantoms (CIPs) are perceived after rather than during cold stimulation, and are localized away from rather than at the site of cooling. Experiments are proposed to test the hypothesis that CIPs, which reversibly mimic clinical dysgeusias, arise when putative tonic inhibition within and between oral sensory systems is interrupted by cold-block. Third, preliminary observations indicate that capsaicin, the prototypical "trigeminal" irritant, can evoke significant bitterness in the circumvallate region of the tongue, and that both sensory irritation and perception of warmth are much weaker there than on the tongue tip. Experiments will investigate the possibility that some glossopharyngeal neurons that contribute to perception of bitterness are sensitive to irritants, and more generally, that the relationship between somesthesis and taste is different on the back of the tongue, where both kinds of stimulation are mediated solely by the glossopharyngeal nerve. Overall, these studies will advance our understanding of oral sensory processing in humans as well as provide data on sensory interactions that may be helpful in understanding the source of certain types of oral sensory pathologies (e.g., dysgeusias).