Regional Variation of Bitter Taste and Aftertaste in Humans

Abstract

Despite widespread and persistent myths of a tongue map, all 5 prototypical taste qualities are sensed over the entire tongue. However, modern psychophysical data also suggest there may be more nuanced differences in suprathreshold intensity across oral loci, especially for bitterness. Here, we test whether bitter stimuli matched for whole-mouth intensity differ in perceived intensity across regions of the oral cavity in 2 experiments. Experiment 1 consisted of a whole-mouth sip and spit approach and Experiment 2 consisted of a spatial taste test using cotton swabs. In Experiment 1, participants (n = 63) rated overall intensity of 3 bitter solutions at 5 different loci (front, middle, back of tongue; roof of mouth; and lip). Temporal effects were explored using in-mouth and aftertaste ratings. In Experiment 2, participants (n = 48) rated the intensity of quinine and Tetralone solutions after solutions were painted on fungiform, circumvallate, and foliate papillae with a swab. After the spatial taste test, participants completed a questionnaire on self-reported beer intake. Analysis of variance results of both experiments show a significant locus by stimulus interaction, suggesting different bitterants were perceived differently across the various loci. This result was apparently driven by low-intensity ratings for Tetralone on the anterior tongue. Aftertaste ratings in Experiment 1 also revealed significant temporal effects: ratings on the anterior tongue decreased for all bitterants and ratings for quinine decreased at all loci. Reasons for these effects are not known but may suggest differential expression of bitter taste receptors or differences in bitter agonist-receptor binding affinity across tongue regions.

Keywords: bitter taste; hops; papillae; spatial taste test; taste perception; tongue map.

Figure 1.

Mean log intensity ratings and standard error of the mean for in-mouth ratings at different oral loci to represent the stimulus effect from Experiment 1. The intensities between stimuli at each locus were compared using t-tests (see text for details). To perform a Bonferroni adjustment for multiple comparisons within a single locus, the P-value shown should be multiplied by 3 (e.g., P = 0.001 would be adjusted to P = 0.003).

Figure 2.

Mean log intensities and standard errors at different oral loci for aftertaste ratings made 15 s after spitting out the sample. Other details are the same as in Figure 1.

Figure 3.

Mean in-mouth and aftertaste log intensity ratings for (a) quinine hydrochloride, (b) sucrose octaacetate (SOA), and (c) Tetralone, a hop extract, from Experiment 1. Comparisons at each locus represent t-tests following a significant locus by time interaction in the repeated measures ANOVA conducted separately for each stimulus (see text for details). To perform a Bonferroni adjustment for multiple comparisons across the 5 different loci, the P-value shown should be multiplied by 5 (e.g., P = 0.005 would be adjusted to P = 0.025).

Figure 4.

Mean log intensity ratings from the spatial taste test used in Experiment 2. Significance for the t-tests between the solutions at each locus is noted. To perform a Bonferroni adjustment for multiple comparisons across the 3 different loci, the P-value shown should be multiplied by 3 (e.g., P = 0.04 would be adjusted to P = 0.12).

Figure 5.

Intensity ratings (logged) for Tetralone on the foliate papillae plotted against self-reported pale ale consumption frequency (annualized, and quarter root transformed) for each participant in Experiment 2. The dashed line represents the correlation across all participants (n = 48), while the solid line represents the correlation among regular pale ale consumers (n = 28) after removing individuals who reported consumption of pale ales 1–2 times per year or less. These non-consumers (n = 20) are shown by the light gray shading in the bottom portion of the graph.