(Author's Abstract) The long-term goal of this research is to understand the influence of genetic and pathological variation in taste sensations on health and quality of life. Humans show genetic variation in taste. This variation is characterized by the number of fungiform papillae (structures that house taste buds) and the ability to taste the bitterness of PROP (6-n-propylthiouracil). Because the fungiform papillae receive innervation from taste, pain, and touch neurons, those who have the highest number of papillae (i.e., supertasters) perceive more intense taste, oral burn (e.g., chilis) and oral touch (e.g., fat) sensations. Genetic taste variation is linked to distaste for bitter foods and preference for sweet and far foods (this includes fruits and vegetables, foods that are important mediators of cardiovascular disease and cancer). Genetic taste variation is also linked to alcoholism and smoking. Pathologies involving the chorda tympani nerve are linked to oral phantoms (sensations in the absence of stimulation); these occur for taste (dysgeusia) and oral pain (burning mouth syndrome). The hypothesis under evaluation is that the chorda tympani nerve (taste, anterior tongue) normally inhibits the glossopharyngeal nerve (taste, posterior tongue) and the trigeminal nerve (pain, anterior tongue). Damage to the chorda tympani thus releases that inhibition leading to intensified taste and pain sensations as well as phantoms (e.g., dysgeusia, burning mouth syndrome) in susceptible individuals. Susceptible individuals appear to be those who have the densest taste and pain innervation (i.e., supertasters). The proposal includes psychophysical and anatomical experiments. One group of experiments will use recent advances in psychophysical methodology and taste anatomy to determine the magnitude of oral sensory differences across nontasters, medium tasters and supertasters. Additional experiments will test the hypothesized release of inhibition on taste and oral burn. The chorda tympani will be anesthetized in normal volunteers. Patients will include those with acoustic neuromas in whom the chorda tympani must necessarily be surgically severed central to its cell bodies; the nerve will degenerate from the cut into the brain possibly leading to central reorganization. Patients will also include those with mastoidectomies or stapedectomies in whom the chorda tympani must necessarily be severed peripheral to the cell bodies; the nerve will degenerate from the cut into the tongue possibly altering peripheral anatomy. A final group of patients are those with taste and/or oral pain phantoms; they will be evaluated for possible damage to the chorda tympani nerve.
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