Different parts of your tongue taste different things. Sweet at the tip, salty on the sides at the front, sour at the sides at the back, bitter at the back. Every primary school science textbook in Australia between roughly 1950 and 2010 had a diagram. Every Year 7 Science Day had a tasting station to confirm it. Sugar at the tip, lemon at the sides, salt next to the sweet, bitter at the back where it makes you gag. The diagram is so embedded in education that your kid's school probably still has the poster.
The taste map is wrong. All five basic tastes (sweet, salty, sour, bitter, umami) are detected by all parts of the tongue. The myth comes from a 1901 paper by German psychologist David Hänig, who measured small differences in threshold sensitivity across regions of the tongue (you do need slightly more sugar at the back than the front to detect it), and from a 1942 textbook by Edwin Boring at Harvard who turned Hänig's subtle threshold data into a hard map with colour-coded zones. Subsequent research, including a definitive 1974 study by Virginia Collings, showed the differences are tiny, the receptors are everywhere, and the diagram is essentially fictional. The reason it stuck around for sixty years is the same reason taste-map stickers got laminated and put on walls: visual aids feel like they explain something. The actual biology of taste is much more interesting (it's distributed, integrated with smell, modulated by genetics, gendered to a small degree, and changes with age) and entirely incompatible with a cartoon tongue with four flavour zones.
Reception
- Virginia Tech: The Myth of the Tongue MapREFERENCE
- Scientific American: Taste MythsREFERENCE