Sensors that detect odours in the nose have been found in human taste cells on the tongue, scientists have discovered.
The finding suggests that interactions between our senses of smell and taste may begin on the tongue and not in the brain, as previously thought.
Until now, taste and smell were considered to be independent sensory systems – but Mehmet Hakan Ozdener, a cell biologist at the Monell Center, Philadelphia, was prompted to challenge this belief when his 12-year-old son asked him if snakes extend their tongues so they can smell.
The discovery could lead to the development of “odour-based taste modifiers”, Ozdener said, which could one day help deter people from consuming excess salt, sugar, and fat.
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While many people equate flavour with taste, the distinctive flavour of most food and drink comes more from smell, the researchers say.
Taste, which detects sweet, salty, sour, bitter, and umami (savoury) molecules on the tongue, evolved as a gatekeeper to evaluate the nutrient value of what we put in our mouths.
Smell provides detailed information about the quality of food flavour, for example – are you eating banana, liquorice or cherry? The brain then combines input from all these senses to create a multi-modal sensation of flavour.
Ozdener and colleagues used genetic and biochemical methods to examine taste cells in culture (where they are grown under controlled conditions outside of the mouth). They found human taste cells contain many key molecules known to be present in sensors found in the nose.
The researchers also used a method known as “calcium imaging”, and found the taste cells responded to odour molecules similar to the sensors found in the nose. This lead them to believe that scent and taste cells interact on the tongue.
Other experiments by the scientists found that a single taste cell can contain both taste and olfactory (scent) receptors, ”[this] provide us with exciting opportunities to study interactions between odour and taste stimuli on the tongue,” said Ozdener.