Think about sipping a sugar-free drink that still tastes sweet. Many of us have puzzled over this illusion. Now scientists at Karolinska Institutet in Sweden reveal how our brains transform smell into taste.

The research, published in Nature Communications, shows that the brain encodes certain aromas as if they were flavors themselves.

How flavor and smell form

Flavor is more than taste. It comes from a combination of gustatory signals and retronasal odors, those aromas drifting from the mouth to the nose.

The insula, known as the taste cortex, was found to integrate these signals earlier than expected. This means the brain does not wait for higher regions to combine taste and smell but merges them immediately into one experience.

Study lead author Putu Agus Khorisantono is a researcher in the Department of Clinical Neuroscience at Karolinska Institutet. 

“We saw that the taste cortex reacts to taste-associated aromas as if they were real tastes,” explained Khorisantono. “The finding provides a possible explanation for why we sometimes experience taste from smell alone, for example in flavored waters.”

“This underscores how strongly odors and tastes work together to make food pleasurable, potentially inducing craving and encouraging overeating of certain foods.”

How the brain links flavor and smell

The researchers tested 25 adults. First, participants learned to identify sweet and savory flavors through combinations of taste and smell.

Later, inside a scanner, they received either tasteless odors or odorless tastes. Algorithms trained on brain responses to actual tastes were then tested on odors alone. The surprising outcome was that odours mimicked the brain’s taste responses.

The study revealed that sweet or savory odors activated the same neural patterns as the corresponding tastes.

This overlap was strongest in the ventral anterior insula, a region connected to olfactory areas. Importantly, the researchers ruled out simple pleasure ratings as the cause. Instead, the brain genuinely encoded odors in a way that matched taste perception.

“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,” said senior researcher Janina Seubert.

“This mechanism may be relevant for how our taste preferences and eating habits are formed and influenced.”

Why flavor and smell matter

The findings highlight the insula as a hub for flavor integration. They also reveal that taste representations can drift over time. Neural patterns of taste identity were less stable across days, echoing results seen in rodent studies.

This suggests that our flavor experiences are dynamic, adapting with exposure, context, and internal states such as hunger, mood, or attention.

A flavor that feels vivid and distinct one day may blur or even shift the next, depending on what the brain has recently learned or anticipated.

This fluid quality points to a system designed not for rigid coding but for flexibility, helping us adjust to changing diets, environments, and cultural influences on taste.

Flavor identity and reward value

The study also observed cross-modal decoding in other regions, such as the orbitofrontal cortex, which is known to encode the value of food.

The researchers propose that the insula forms a shared flavor identity, while the orbitofrontal cortex evaluates its reward value. This dual process could explain why certain odors make foods irresistible and shape long-term eating habits.

The team now wants to test external smells, or orthonasal odors. These are the scents we encounter before eating, like walking past bread or pastries.

“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,” said Khorisantono. “If so, this could have a significant impact on the foods we choose to consume.”

How flavor and smell affect health

This research reframes flavor as a deeply integrated brain process. Smell and taste are not separate streams but overlapping codes that can trick the brain into tasting without tasting.

Beyond solving everyday mysteries like sweet-tasting flavored water, the work raises questions about cravings, overeating, and how our diets are shaped by environments filled with powerful aromas.

The research also suggests that everyday exposure to food-related smells in supermarkets, restaurants, offices, and even advertising spaces may influence us more than we realize.

These aromas may prime the brain to expect certain tastes, creating a loop where scent alone can nudge us toward food choices we might not otherwise make.

Over time, this subtle influence could shape eating habits, nutritional patterns, and even health outcomes, revealing how deeply our sensory world directs behavior long before conscious decisions take place.

The study is published in the journal Nature Communications.

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