For decades, teachers and textbooks have perpetuated the idea that different parts of the tongue are exclusively correlated with different basic tastes. However, this idea is a misconception with no basis in modern physiology. In reality, taste buds are capable of detecting all five modalities of taste –– sweetness, sourness, saltiness, bitterness, and umami –– with individual perception of each taste being influenced by various factors like age, genetics, and cultural background.
This common misconception of a “tongue map” is believed to have originated from Dr. E. Boring’s poor analysis of a German paper, “Zur Psychophysik des Geschmackssinnes,” On the Psychophysics of Taste, written by D.P. Hänig in 1901. The original paper had merely identified slight variations in sensitivity for detecting each of the basic tastes across the tongue. Dr. Boring’s paper, by contrast, erroneously exaggerated these minute differences and transformed them into a suggestion that each part of the tongue was exclusively responsible for a different taste.
This proposal became swiftly integrated into the popular and academic understanding of the human sense of taste until it was at last disproved by researcher Virginia Collings in 1974. Like in Dr. Häning’s original paper, Collings discovered that the differences in concentrations of taste receptors across the mouth were so slight as to produce an altogether negligible effect on taste.
Modern physiology understands taste buds to contain clusters of taste-receptor cells responsible for mediating the human sense of taste. Within a given taste bud, some receptor cells are specialized to sense sweetness, while others are more primed to sense sourness, saltiness, bitterness, or umami. When a person consumes food or drink, each of these specialized cells sample oral concentrations of a large number of molecules contained within the said food or drink and thereafter report the overall sensation of taste to the brainstem.
The perception of the more pleasant tastes of sweetness and umami is mediated by a set of receptors called T1R. These receptors come in pairs, with T1R2 and T1R3 working together to bind molecules associated with sweetness, and with T1R1 and T1R3 working together to bind molecules resulting in savouriness, such as L-glutamate and L-amino acids. Bitter and sour flavours are detected by a separate set of receptors called T2R and TRP, respectively. Interestingly, the scientific literature on the perception of saltiness is still relatively limited and remains an area of ongoing research and investigation.
The physiology of taste is more complicated than the model of the “tongue map,” so why is the map so persistent in modern education and culture? Perhaps it is because people enjoy the simplicity and visual appeal of a map wherein sections of the tongue can be divided into neat, clear categories. However, modern research shows that the physiological mechanisms of taste are much more subtle and arise from the presence of large numbers of specialized receptor cells in taste buds that enable all parts of the tongue to sense all five modalities of taste.