Dr Karl › Dr Karl's Great Moments In Science

Tastebud map a sensational tale

While commonly thought to sense only four tastes, our tongues can actually sense five. Dr Karl pokes his tongue out at the so-called taste-bud map of the human tongue.

Last time, I began by talking about the basic anatomy and physiology of taste.

Now most of us have heard that there are four basic taste sensations and that they are each localised to a specific part of the tongue.

You might have seen the tongue taste map showing that we sense sugar at the tip of the tongue, sour along the sides and bitter at the back of the tongue.

This belief is wrong in two different ways. First, there are five basic taste sensations not four. Second, we sense all five taste sensations all around the tongue.

How did this wrong belief get passed along to generations of school and university students?

It began way back in 1901, when a young PhD student, called Hanig, published his thesis in the journal, Philosophische Studien.

He knew that the taste buds were most densely distributed around the perimeter of the tongue. He wanted to see if the then-known four basic taste sensations were detected differently across the tongue.

He used sucrose to test for the sensation of sweetness, and quinine to test the sensation of bitter. He also used very dilute hydrochloric acid to test for the sensation of sour and, of course, used salt to test for saltiness.

Dr Hanig found that all four tastes could be detected around the whole perimeter of the tongue. Yes, there were slight differences around the perimeter of the tongue, but they were quite small.

Sure, sweet was best detected at the tip of the tongue, and worst detected at the base of the tongue, but it was still very well-detected all around the perimeter of the tongue.

The sensation of bitter was the opposite. Worst at the tip, best at the base, but still very well-detected all around the perimeter of the tongue.

And similarly sour was best-detected at the middle of the sides of the tongue and worst-detected at the tip of the tongue. But it was still very well-detected all around the perimeter of the tongue.

Finally, the sensation of salt was detected fairly equally all around the perimeter of the tongue.

Dr Hanig then made a rather impressionistic and very rough graph of his findings. It was so rough that he didn't even have any values or numbers on the vertical axis of his graph.

He just wanted to show that for the sensations of sweet, sour and bitter, there was a slight variation around the perimeter of the tongue.

In 1942, the distinguished experimental psychologist, Edwin G. Boring, wrote about Dr Hanig's work. He transformed Dr Hanig's data, and in the process, unfortunately made a new graph with added numbers where previously there had been none. He also smoothed off a few bumps from Dr Hanig's data.

Dr Boring did not, at any stage, write that for, say, sweetness the sensation was greatest at the tip of the tongue and virtually zero everywhere else.

But if you didn't understand physiology, you could easily misinterpret Dr Boring's work and graphs. And so other people (and we're not sure who they are) did misinterpret Dr Boring's misinterpretation of Dr Hanig's original work.

They made the familiar tongue taste map, with the sensitivity for sweet only at the front, sour only at the sides and bitter only at the back.

And that's how the familiar, but very wrong, tongue taste map came into existence, to be taught to generations of children, teenagers and gullible grown-ups.

But here's something odd. This map claims that sweetness, and only sweetness, is detected at the tip of the tongue. But if you place some salt on the tip of your tongue, you definitely taste salt.

In the face of such simple evidence, why on Earth did people continue to believe such a wrong thing from the middle of the 20th Century right up to the present day?

In 1974, Virginia Collins did try to set the record straight. She also found taste buds in places other than the tongue, including on the soft palate on the roof of your mouth and on the epiglottis (the movable flap that stops food going down your windpipe or trachea).

But there's another thing wrong about the four basic tastes being mapped onto the tongue.

It's that there are five basic tastes, not four. The fifth one is called umami.

Umami was first identified way back in 1901, by the Japanese scientist Kikunae Ikeda.

It's found in some Japanese sea vegetables, soy sauce, ripe tomatoes, smelly cheeses, meat broths, grains, beans and well-grilled meats.

It's also the taste of monosodium glutamate, which Ikeda isolated and patented.

Who knows, if in the future, we'll identify more than the five basic tastes? Maybe for that, we'll need the sixth sense.

^ to top