Study reveals how the brain interprets certain aromas as taste

Flavored drinks without sugar can be perceived as sweet - and now researchers know why. A new study from Karolinska Institutet in Sweden, published in the journal Nature Communications, reveals that the brain interprets certain aromas as taste.

When we eat or drink, we don't just experience taste, but rather a 'flavor'. This taste experience arises from a combination of taste and smell, where aromas from food reach the nose via the oral cavity, known as retronasal odour. Researchers at Karolinska Institutet have now shown that the brain integrates these signals earlier than previously thought - already in the insula, a brain region known as the taste cortex - before the signals reach the frontal cortex, which controls our emotions and behavior.

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

Putu Agus Khorisantono, lead author, researcher at the Department of Clinical Neuroscience, Karolinska Institutet

The study involved 25 healthy adults who were first taught to recognise both a sweet taste and a savoury taste 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.

May be relevant for our eating habits

The results showed that aromas that are perceived as sweet or savoury not only activated the same parts of the brain's taste cortex as the actual tastes but that they evoke similar patterns of activation. This overlap was particularly evident in the parts of the taste cortex that are linked to the integration of sensory impressions.

"This shows that the brain does not process taste and smell separately, but rather creates a joint representation of the flavor experience in the taste cortex," says the study's last author, Janina Seubert, senior researcher at the same department at Karolinska Institutet. "This mechanism may be relevant for how our taste preferences and eating habits are formed and influenced."

The researchers now plan to investigate whether the same mechanism applies to external smells, known as orthonasal odors.

"We want to find out whether the activation pattern in the brain's taste cortex changes from salty to sweet when we walk from the cheese aisle to the pastries in the supermarket," says Putu Agus Khorisantono. "If so, this could have a significant impact on the foods we choose to consume."

The study was conducted in collaboration with researchers in Turkey and was funded by the European Research Council (ERC) and the Swedish Research Council.