Taste cells in the tongue contain the same smell receptors as those found up our noses, researchers say.
The findings suggest that the main components of food flavour, taste and smell, work together on the tongue, rather than being first combined in the brain.
The researchers were inspired to investigate whether human tongues could smell by snakes, which are known to sniff at the air by flicking out their forked tongues.
By learning exactly how the sensation of flavour is created, the experts say, we may one day develop taste-modifying agents to help combat diet-related diseases.
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The researchers found that human taste cells contain many of the same key molecules as found in olfactory (smell) receptors in our noses (stock image)
Now, researchers from the Monell Chemical Senses Center in Philadelphia and the New York University have used genetic and biochemical methods to study human taste cells grown in a dish.
The researchers found that human taste cells contain many of the same key molecules as found in olfactory (smell) receptors in our noses.
Next, the team used a technique known as calcium imaging to show that their taste cells respond to odour molecules in the same way as olfactory receptor cells.
Other tests by the researchers revealed that a single taste cell on the tongue can contain within it both taste and smell receptors.
‘Our research may help explain how odour molecules modulate taste perception,’ said senior author Mehmet Hakan Ozdener, who is a cell biologist at the Monell Center.
‘This may lead to the development of odour-based taste modifiers that can help combat the excess salt, sugar, and fat intake associated with diet-related diseases such as obesity and diabetes,’ he added.
For example, food could be made to taste sweeter than it really is, helping to minimise the desire to eat more.
Although we commonly think that we discern the characteristic flavours of food and drink through our sense of taste, it is our sense of smell that actually plays the more important role in this process.
Taste — which can identify bitter, salty, sour, sweet and umami (or savoury) molecules on our tongues — actually evolved to help us evaluate the nutritional values and potential toxicity of foodstuffs.
In contrast, it is our sense of smell that provides us with detailed information on the flavour of foods — enabling us to distinguish between, say, strawberry and chocolate.
It had previously been thought that it was only in the brain that that taste and smell were combined to create the overall sensation of flavour.
The findings of the new study, however, suggest such that these two senses may come together much earlier than was thought.
Dr Ozdener was inspired by snakes to study whether human tongues might also be able to smell.
Snakes are known to flick out their receptor-full tongues to sniff the air.
Dr Ozdener was inspired by snakes to study whether human tongues might also be able to smell. Snakes are known to flick out their receptor-full tongues to sniff the air (stock image)
With this initial study complete, the researchers are now working to determine if the olfactory receptors on the tongue are mainly located in cells that handle particular tastes — such as salty or sweet detecting cells.
Other studies planned will explore how odour molecules might alter the responses of taste cells and, by extension, our overall sensation of taste.
‘The presence of olfactory receptors and taste receptors in the same cell will provide us with exciting opportunities to study interactions between odour and taste stimuli on the tongue,’ Dr Ozdener said.
In addition, the new findings may also provide a new tool with which scientists can study how we smell things — as it remains unclear which molecules activate the majority of the around 400 different types of human olfactory receptors.
The taste cells cultured in the lab could be applied to help screen molecules and identify those which activate given receptors.
The full findings of the study were published in the journal Chemical Senses.
HOW DOES THE HUMAN OLFACTORY SYSTEM WORK?
Smelling is a complex process.
The olfactory systems detects molecules in the air.
Breathed into the nasal cavity, odorous molecules come into contact with olfactory epithelial tissues at the top of the nose.
Each molecule stimulates multiple chemical receptor cells.
The olfactory nerve passes the information from the receptor cells into the brain for processing.
The information transmitted includes measures of the odour intensity and quality.