Smelling with your tongue

A new study suggests that besides tasting, the human tongue may be able to smell its environment. Many animals already taste and smell their surroundings through the same organ in their body. 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.

In humans, taste and smell were considered as complementary senses that operate individually. 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. Studies published earlier have shown 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 other researchers to investigate whether mammals — including humans — can also smell with their tongues. In the new study, the research 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 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 provides exciting opportunities to study interactions between odor and taste stimuli on the tongue.

The research may help explain how odor molecules modulate taste perception and could lead to the development of odor-based taste modifiers that can help combat the excess salt, sugar, and fat intake associated with dietrelated diseases, such as obesity and diabetes