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This diagram is the result of research done over 100 years ago. It has largely been abandoned by modern biologists, although it remains published in science textbooks. The gist is that the taste buds are localized in specific areas of the tongue, and that sensitivity to specific tastes are much higher in those areas. More recent research states that these tastes are distributed over the entire tongue, although certain areas might be slightly more sensitive to certain tastes than others. As such, the "new taste" of umami has not been placed on the map.
Personally, I give a little more credit to the tongue map than is the current scientific opinion. This stems from my personal "research" into the subject. I was coding one night with a 1 lb. paper bag of sour fruit salad on my desk. Piece after piece of acid-coated sugar globules found their way into my mouth. After a while, I realized I had eaten about 3/4 lb. of it. I also noticed that my tongue was in considerable pain. For a week afterwards, I had painful red sores on the sides of my tongue, precisely where the tongue map shows the sour taste buds to be. I refuse to deny the validity of this plain-as-day evidence. Ever since then, I purchase my sour fruit salad in four separate 1/4 lb. bags.
A Scientific American
article was published recently on the subject:
More in-depth info can be found at: