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# Urology Pearls

## Taste and flavors: Mouth’s marvelous map

In my latest article about the sense of taste, I told you that the tongue map you have learned about in biology class was all wrong.

The human tongue has, on average, about 7,500 taste buds. Each taste bud has the shape of a closed rose with its small opening facing the surface of the tongue. In each taste bud there are 50 to 150 cells, bundled together like a cluster of bananas. All of these cells belong to only three different groups. One type is activated by substances that taste salty; another by substances that taste sweet, bitter, and savory; yet a third type is activated by substances that taste sour. Once activated, these cells produce tiny electrical currents, signals that travel, through nerve fibers, into the brain.

I asked myself, ‘With only three different “electrical switches,” how can we sense so many different flavors?’

To address this interesting question, I reminded myself of the ice cream challenge I was presented with during a high school class in combinatorial mathematics. I remembered questions such as: suppose you are working at an ice cream parlor. How many different combinations of a three-scoop ice cream dish could you produce out of only three different flavors, say chocolate, vanilla, and strawberries. The correct answer had been 9 (you could have the following combinations: CCC, VVV, SSS, VCC, SCC, CVV, SVV, CSS, VSS). But, with each additional flavor, say an additional scoop of pistachio, the number of possibilities would double! Adding an option of a scoop of pistachio would double the number of experiences, and so would adding a choice ‘a plastic cup, or a waffle cone,’ and ‘with chocolate sprinkles on top, or without,’ or ‘would you rather eat your dish here, or have it ‘to-go?'” The number of possible experiences will grow quickly, or, to be mathematically exact, exponentially!

Then I thought, ‘Our sense of taste may be based on only 3 “electrical switches,” but our sensation of taste must also multiply quickly to almost unlimited possible experiences.’ The messages, once produced in our taste buds, are transferred via cranial nerves into the brainstem. From there, information travels to the thalamic, subcortical, and cortical areas of the brain where it is integrated with information from other sources.

How complex is this interaction? Looking for evidence, I stumbled upon an article published in 2014, in Science. In it, Bushdid and colleagues at the Rockefeller University in New York, found that the human nose, with its 400 types of scent receptors, can decipher at least 1 trillion different odors! They proved this by asking 26 study participants to identify certain scents in different mixtures the researches concocted out of a collection of 128 different odor molecules.

All of a sudden, I could truly understand the immense variability of flavors. The sense of taste was no longer a collection of electrical lines transporting a single, simple piece of information such as ‘this is sweet, salty, or sour.’ Instead, it was a network of processors that draw information from several different sources–the sense of smell, the texture and temperature of food, and mental states such as memory, and hunger. In my mind, with each bite, with each gulp, these processors talked with each other, modified each other, and, eventually, translated this information into a unique experience.

I could easily remember instances in my life where the context of food consumption was integral to the experience of tasting; a dinner I had at the end of a long Yom Kippur fasting; a visit with a friend to a favorite restaurant; my Grandma’s stuffed peppers.

The richness of our sense of taste can be understood by mathematical models. With each additional variable, the number of possible experiences doubles. Nature is generous, and it does magic at a very low cost; after all, doubling the number of experiences is as easy as throwing one more additional receptor, or sensor to the mix. It is Nature’s way of giving us a free ride, a two-for-the-price-of-one ticket to the immense world of flavors.

And yet, with all its richness, our sense of taste is still limited. It often fails to inform us about harmful, or toxic ingredients in our food. And it is yet to develop an alarm system that would advise us to stop eating when our nutritional needs are met. This is the reason, why most people, including myself, need to know more about diets and healthy eating.

Editor’s note: Dr. Shahar Madjar is a urologist at Aspirus and the author of “Is Life Too Long? Essays about Life, Death and Other Trivial Matters.” Contact him at smadjar@yahoo.com. He will be signing his new book “Take Love Twice Daily” on Valentine’s Day, Friday, at 5 p.m., at Snowbound Books in Marquette.