Mapping the tongue : a novel approach to explore cross-cultural differences in chemosensory perception

The fungiform papillae density (FPD) of the human tongue is considered as an index for responsiveness to oral chemosensory stimuli, which varies among different populations. Manual counting and visual analysis of digital pictures represent the most popular techniques for FPD assessment, despite the limitations and bias- related. The aim of the study was to set up a novel procedure for an automated assessment of FPD and define a specific tongue mapping for different populations. Data were collected on 228 subjects, balanced according to gender, age (19-55 years) and ethnicity (33% Chinese; 34% Danish and 33% Italian). Intensity ratings of PROP bitterness were obtained to characterize subjects’ taste responsiveness. FP numbers were manually counted using the three commonly applied methods (Method 1 according to Nachtsheim & Schlich, 2013; Method 2 according to Masi et al., 2015; Method 3 according to Essick et al., 2003) and through a novel tool for image analysis, in which the whole tongue was analyzed and mapped. This approach will provide an anatomically oriented tongue coordinate system, taking into account specific subject tongue shape, defining a density map of detections related to chemosensory perception (e.g. PROP responsiveness and tactile acuity) and cross-population differences among subjects. Overall, all the counting approach applied correlated to each other. All the methods provided clear discrimination, in terms of FPD, among PROP taster status groups (supertasters, medium-tasters, and non- tasters), albeit in different ways. Methods 1 and 2 highlighted differences between supertasters and the other two groups, while Method 3 allowed better discrimination between non-tasters and taster subjects. Moreover, the visual analysis of tongue pictures provided an evaluation of the size and distribution of fungiform papillae, defining a specific ethnicity mapping of the whole tongue, which could get an insight into the interplay among aspects related to differences in chemosensory perception among populations.