Regional Differences in Suprathreshold Intensity for Bitter and Umami Stimuli

The sense of taste is often referred to as a 'nutritional gatekeeper', thought to have evolved to indicate energy sources and prevent ingestion of potential toxins. Fungiform papillae are structures on the anterior tongue in which taste buds are situated. They are concentrated at the tongue's tip and they can provide a useful estimate of overall taste bud density for taste research. Some reports suggest taste perception may differ subtly across tongue regions, irrespective of FP number. Other data show an association between taste intensity perception for the bitter compound 6-n-propylthiouracil (PROP) and FP density. However, contradictions exist in the literature, with more recent, larger studies suggesting little or no association between FP number and perceived taste intensity. Many studies have examined the relation between FP density and PROP perception, while other tastes have been less thoroughly studied. Here, in a cohort of mainly Caucasian individuals, aged 18-45 years, recruited from the campus of a large rural university, we examined regional and whole mouth taste intensities, and FP density using an updated method of a digital still photography method first described in 2005. We found regional differences in suprathreshold intensity. Although all taste sensations were experienced all over the tongue, once again disproving the mythical tongue map, we also observed bitter and umami taste perceptions to be significantly greater on the posterior tongue than on the anterior tongue. In contrast, there were no regional differences observed for sweet, salty, or sour tastes. The relation of FP density to whole mouth intensity of 6-n-propylthiouracil and to the intensity of saltiness of NaCl, sweetness from sucrose or from Acesulfame-K, bitterness of quinine, or burning from capsaicin delivered to different regions of the tongue are also discussed.