First of all, the information given in most textbooks depicting a taste map of the tongue, i.e., divided into regions where it can detect salty, sour, sweet and bitter sensations, like zip codes, is completely wrong. There are no fixed areas for the fundamental tastes. The sense of taste as far as the tongue is concerned, is more like an essay exam, which the teacher has to process, giving weight to certain criteria to be processed for the brain’s assessment of what it tastes like. This is what scientists Dr. David Smith and Dr. Robert Margolskee with their colleagues learned from their studies on the sense of taste (Scientific American, March 2001).
True, the taste buds in the tongue are located within those tiny protrusions called papillae which in turn are found along the vertical line center of the tongue, the inner sides, scattered along the inner tongue near the tonsils, as well as the outer portion that is readily seen when you stick your tongue out. In other words, they are everywhere. But while there are no specific areas responsible for detecting certain tastes, there are certain proteins or "ion channels" with which the saliva-dissolved chemicals from the food we eat called "tastants" interact, causing electrical changes in the taste buds that send chemical signals to the brain. And whola! You can now recognize the taste of food!
The four fundamental tastes – sweet, bitter, sour and salty – are so because no matter how different the chemical structures of the food we taste are, we sense them as such or a combination of any or all of them. Take, for instance, sugar substitutes like asparteme and saccharin. They are chemically different from sugar, yet we sense them as "sweet" like we do with sugar. Or bittermelon or ampalaya and certain medicines, or even dark chocolate – they do not necessarily share the same chemical make-up but we characterize them in a blanket manner as "bitter." Some researches on taste have identified a possible fifth element called "umami" (only the Japanese seem to have a word for it). It is apparently elicited by a chemical from meat, fish and legumes that could also be found in the form of MSG (monosodium glutamate). I have a strong hunch, though I cannot back this up scientifically for now, this "umami" sensation is what infanticipating or PMS women crave for. So digressing for a moment, if you are what they call a "hormone hostage" by a pregnant or PMS woman, you may want to consider as damage control, indulging her in what she wants to gorge on during that captive period. I should look into this in the future because it seems that "cravings" for certain tastes, the studies showed, are really your body’s way of telling you what you need to eat. Evidence of previous researches has shown that undernourished humans instinctively chose food that are rich in nutrients they badly needed and that these cravings did indeed also produce the chemicals in the body required to process this food. Though why it is required by an infanticipating woman that the very rare fruit she wants has to be snatched from a certain backyard tree from some island far and away, I think, is beyond the scope of physical science research.
Aside from the fundamental four (or possibly five) tastes, the studies also found that the tasting process also includes an assessment by the brain of taste as either pleasant, unpleasant or neutral and even react to taste associated with how it "feels" like, i.e, by texture and temperature. This dimension to taste is crucial to our survival as physical beings as this guides our senses on what to ingest and what to avoid. When I was three, my cousins who numbered six then, appointed me as "leader" in a game of "follow the leader." It was all going swell until the last portion when I saw a really attractive plant and led all my cousins to eating what turned out to be little red hot chilis! We then all went scampering to our mothers for relief! Up to now, my cousins and their parents tell that story with amusement and a detectable tinge of reproach while looking at me. But unlike rats which have a better memory association of taste with what can be lethal to them (that is why it is difficult to trap mouse with "food"), I grew up to like spicy food. I can imagine our human ancestors then on a trial-and-error mode to what they can eat without getting themselves maimed or killed. I set off in a fancy trying to imagine what the human who discovered you can eat langka (jackfruit), durian or rambutan, was thinking, or the really desperate human who had to smash the coconut and the walnut to be able to luxuriate in their tastes. If I had been born that early, I am sure I would have passed on the chance since I would be one of those who would never think of needing to use a hammer-like tool to be able to snack. But luckily, our ancestors had better instincts that some of us, including myself, still lack, that we now enjoy the taste of the uncountable menu of life.