The notion that the tongue is mapped into four areas—sweet, sour, salty and bitter—is wrong. There are five basic tastes identified so far, and the entire tongue can sense all of these tastes more or less equally.

As reported in the journal Nature this month, scientists have identified a protein that detects sour taste on the tongue. This is a rather important protein, for it enables us and other mammals to recognize spoiled or unripe food. The finding has been hailed as a minor breakthrough in identifying taste mechanisms, involving years of research with genetically engineered mice.

This may sound straightforward but, remarkably, more is known about vision and hearing, far more complicated senses, than taste.

Maps like this have been around for ages. But they are wrong. LiveScience Bad Graphic. Image: stock.xchange

Only in recent years have taste receptors been identified. One of the first breakthroughs in taste research came in 1974 with the realization that the tongue map was essentially a century-old misunderstanding that no one challenged.

You might know the map: The taste buds for "sweet" are on the tip of the tongue; the "salt" taste buds are on either side of the front of the tongue; "sour" taste buds are behind this; and "bitter" taste buds are way in the back. Wineglasses are said to cater to this arrangement.

The tongue map is easy enough to prove wrong at home. Place salt on the tip of your tongue. You'll taste salt. For reasons unknown, scientists never bothered to dispute this inconvenient truth.

The map has frustrated many a grade-schooler, including me, who couldn't get the experiment right in science class. I failed for insisting I could taste sugar in the back of my tongue.

In fact, there's more to taste than sweet, sour, salty and bitter. Most scientists agree that there's a fifth distinct taste, called umami, identified by a Japanese scientist named Kikunae Ikeda in the early 1900s (and ignored by the West for most of the twentieth century). This is the taste of glutamate. It is common in Japanese foods, particularly kombu, a type of sea vegetable similar to kelp, and in bacon and monosodium glutamate (MSG), which Ikeda isolated and patented. There's considerable debate about the existence of a sixth taste receptor for fat, too.

The tongue map dates back to research by a German scientist named D.P. Hanig, published in 1901. Not familiar with Japanese cuisine, Hanig set out to measure the relative sensitivity on the tongue for the four known basic tastes. Based on the subjective whims of his volunteers, he concluded that sensitivity to the four tastes varied around the tongue, with sweet sensations peaking in the tip, etc. That's all.

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In 1942, Edwin Boring, a noted psychology historian at Harvard University, also apparently unfamiliar with Japanese cuisine, took Hanig's raw data and calculated real numbers for the levels of sensitivity. These numbers merely denoted relative sensitivities, but they were plotted on a graph in such a way that other scientists assumed areas of lower sensitivity were areas of no sensitivity. The modern tongue-map was born.

In 1974, a scientist named Virginia Collings re-examined Hanig's work and agreed with his main point: There were variations in sensitivity to the four basic tastes around the tongue. (Wineglass makers rejoiced.) But the variations were small and insignificant. (Wineglass makers ignored this part.) Collings found that all tastes can be detected anywhere there are taste receptors—around the tongue, on the soft palate at back roof of the mouth, and even in the epiglottis, the flap that blocks food from the windpipe.

Later research has revealed that taste bud seems to contain 50 to 100 receptors for each taste. The degree of variation is still debated, but the kindest way to describe the tongue map is an oversimplification. Why textbooks continue to print the tongue map is the real mystery now.

As for the myth that the tongue is the strongest muscle in the body, this doesn't seem to be true by any definition of "strength." The masseter, or jaw muscle, is the strongest due its mechanical advantage, in which the muscles attach to the jaw to form a lever. The quadriceps and gluteus maximus have the highest concentration of striated muscle fibers, a pure measure of strength. The heart is the strongest muscle if you measure strength as continuous activity without fatigue.

The tongue, on the other hand, wears out quickly—at least with some people.

Christopher Wanjek is the author of the books “Bad Medicine” and “Food At Work.” Got a question about Bad Medicine? Email Wanjek. If it’s really bad, he just might answer it in a future column. Bad Medicine appears each Tuesday on LIveScience.