Fact
The tongue map is completely made up
Sweet at the tip, bitter at the back. It was a mistranslation, and it has been in textbooks for a century.
The familiar diagram came from a 1901 German paper reporting slight regional differences in sensitivity, mistranslated and redrawn into distinct zones. All five basic tastes are detectable across the whole tongue. You can prove it in seconds by putting sugar on the back of your tongue.