Thermal Taste

TOUCH the tip of your tongue to an ice cube for a few seconds. If the flavour starts turning salty, you’ve passed the thermal taste test. Such an experiment exemplifies the finding that the temperature of the tongue tempers taste. Specifically, researchers have discovered that heating the tip of the taste and speech organ evokes sensations while cooling it produces sour and salty flavours. In other words, depending on the temperature of your food you can consider whether the meal is tasty or not.
The temperature-taste tie could help explain how the brain is told what the tongue is experiencing, said study authors Alberto Cruz and Barry Green of the Yale School of Medicine in New Haven, CN. They described the first evidence that warming and cooling regions of the tongue can produce tastes.
While pervious electrical recordings of taste nerves had pointed to their sensitivity to heat and cold as well as to chemicals, scientists have puzzled over whether the brain interprets such terminal stimulation as taste or as temperature. New research showed cooling the tongue tip about 15 degrees Celsius below normal mouth temperature produced a sour taste, chilling it another 10 degrees elicited a salty flavour and rewarming it induced the sensation of a sweet taste. While some of the 16 subjects noted no difference, many others reported a surprising “clarity and strength” in the effect, the researchers said.

Researchers have absolutely no idea about the mechanism underlying the phenomenon. These findings remind us how little we know about the coding of sensation in the oral cavity. How the nervous system filters out activity due to changes in the temperature, pH, and various concentration gradients from those associated with tastes per se.
Understanding how the nervous system is fooled into registering a temperature change as taste, may help us understand some of the basic processes in taste coding.
Knowing that manipulating the tongue’s temperature can produce the same gustatory effects, as do chemicals, provides clues to the physiology of taste. It was discovered that specific tastes can be produced by temperature stimulation, just as certain chemicals can evoke only certain taste qualities.
The implication is that the tongue’s receptors that respond to chemicals have properties that also make them sensitive to a change in temperature. Furthermore, the receptors that respond to cold and heat likely are not uniformly distributed since the thermal taste differs on different parts of the tongue, the tip being the most prone to perceive sweetness, the side, sourness, and the back, bitterness.

Thermal taste probably does not affect the taste of most foods and beverages because the temperature conditions that produce it are rarely encountered during eating and drinking, and when they are, the chemical taste of foods and beverages tend to mask thermal tastes.

Frozen foods and desserts provide the best opportunity for determining how thermal taste can influence flavour. To a salt-sensitive person, for example, an ice cube held to the tip of the tongue will begin to taste salty after a few seconds. The study is significant in at least three ways: First, thermal taste answers a very long-standing question about the temperature sensitivity of the taste nerves and indicates that the (central nervous system) interprets this stimulation as taste, not as thermal sensation.
Second, the phenomenon raises several questions about the physiology of taste. Most notably, what is it about transduction mechanisms for the types of temperature change? And the third, the differences in incidence of thermal taste on different parts of the tongue and across individuals indicate that there is a great deal of diversity in taste innervations. Finding out more about this diversity should provide important new information about how the taste system works and how the perception of taste varies from person to person.

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