Tasting with Your Nose: Brain Imaging Reveals Role of Retronasal Olfaction

By Stephanie Feuer

The last time you had a cold, you likely noticed that your food tasted bland. That’s because smell is part of what we experience as flavor, and a key contributor is retronasal odor. 

A new study from Karolinska Institutet in Sweden, published in Nature Communications, sheds new light on exactly how our brains build the perception of flavor and shows that we interpret certain aromas as taste. Their results reveal that taste-odor integration happens in the insula, a deep structure within the brain, located between the cerebral cortex and the limbic system  processes sensory information.

 “We saw that the taste cortex reacts to taste-associated aromas as if they were real tastes,” lead author Putu Agus Khorisantono says. “The finding provides a possible explanation for why we sometimes experience taste from smell alone, for example in flavoured waters. This underscores how strongly odours and tastes work together to make food pleasurable, potentially inducing craving and encouraging overeating of certain foods.”

Not only can retronasal smells trick the brain, researchers found that these signals are processed together.

Janina Seubert says that “the brain does not process taste and smell separately, but rather creates a joint representation of the flavor experience in the taste cortex. This mechanism may be relevant for how our taste preferences and eating habits are formed and influenced.”

The study involved 25 healthy adults with verified normal sense of taste and smell. They were  first taught to recognise sweet tastes (golden syrup, lychee and raspberry) and savory tastes (smoky bacon, chicken and onion) through combinations of taste and smell. This was followed by two brain imaging sessions using functional magnetic resonance imaging (fMRI), in which the participants were given either a tasteless aroma or a taste without smell. The researchers trained an algorithm to recognise patterns in brain activity for sweet and savoury tastes, and then tested whether the same patterns could be identified when the participants were only given aromas.

The researchers conclude that their findings “provide a neural basis for the quasi-synaesthetic perception of taste and retronasal odor during food consumption.” Their work explains that when our brains are tricked into thinking something tastes sweet based on its smell - like flavored, unsweetened water -  it is because “odors and taste evoke comparable neural codes.”