A new study suggests that the human tongue may be able to do much more than taste.
Unlike humans and other mammals, not all animals have noses with smell receptors, but this does not mean that they have no sense of smell.
For instance, crabs capture smells through the sensory bristles on their antennae, while snakes, although they do have nostrils, actually smell better through their mouths, "fishing" for scents with their forked tongues.
However, smell and taste usually work together in allowing animals to navigate the world. This collaboration is obvious in snails, for instance, whose lower tentacles allow them to smell and taste their environment.
Taste and smell also work as complementary senses in humans. Olfactory (smell) inputs from the nostrils and gustatory (taste) inputs from the tongue interact in the brain to create a complete picture of what, for example, a person is preparing to eat or drink.
Nevertheless, so far, researchers have tended to believe that the senses of taste and smell operate individually in humans and other mammals.
However, a study that Current Biology published earlier this year found that when scientists removed the taste cortex from the brains of rats, this affected not only the animals' ability to perceive taste but also their sense of smell.
Similar research has now led Dr. Mehmet Hakan Ozdener and colleagues from the Monell Center in Philadelphia, PA, to investigate whether mammals — including humans — can also smell with their tongues.
Taste cells could both taste and smell
In the new study, the results of which appear in the journal Chemical Senses, Dr. Ozdener and team used both genetic and biochemical techniques to determine whether the taste buds of mice, called mouse taste papilla cells, might be able to respond to odor molecules. They then tested laboratory cultures of human fungiform taste papilla cells.
First, the researchers found that mouse taste papilla cells actually contained olfactory receptors and that the same was true of the cultured human taste cells.
Following this, the team used a scientific technique called calcium imaging to assess how the cultured taste cells responded to odor molecules, which revealed that the taste cells interacted with them in a very similar way to regular smell receptor cells.
Further experiments then also showed, for the first time, that one taste cell can contain receptors for both smell and taste. This discovery could help shed new light on just how closely taste and smell work together to alert us to the desirability of a particular food, for instance.
"The presence of olfactory receptors and taste receptors in the same cell will provide us with exciting opportunities to study interactions between odor and taste stimuli on the tongue."
Dr. Mehmet Hakan Ozdener
"Our research may help explain how odor molecules modulate taste perception," Dr. Ozdener also notes, adding that it "may lead to the development of odor-based taste modifiers that can help combat the excess salt, sugar, and fat intake associated with diet-related diseases, such as obesity and diabetes."
In the future, the research team hopes to find out whether only certain taste cells contain smell receptors and to what extent the odor molecules that taste cells capture can change how an individual perceives specific tastes.