The nose is a clever smell prediction system

Think your sense of smell is just some animal instinct, ready to react when you sniff a tasty snack or a whiff of danger? Think again. A new study reveals that your nose is an amazingly clever prediction machine, constantly working behind the scenes to help you make sense of the world.

The nose vs. eyes (and ears)

Scientists at Stockholm University discovered that our sense of smell is way more influenced by expectations and other sensory cues than our sight or hearing. This discovery challenges the common perception of smell as a basic, reactive sense.

“The main finding is that smelling was much more dependent on predictions than vision was. This is interesting because many people think that smell is primitive and reactive, when our research shows it is in fact quite sophisticated and proactive,” said Stephen Pierzchajlo, PhD Student at the Department of Psychology, and main author of the study.

Think about it: a strange smell in your apartment instantly makes you look around to discover its source. Or perhaps the scent of cinnamon rolls triggers the expectation of seeing a cozy bakery. These aren’t random reactions.

This research supports the “predictive coding” theory of the brain, which suggests our brains are continuously making predictions about what we’ll experience next. Our sense of smell appears to be exceptionally skilled at this predictive game.

Smell and prediction

When we smell something unexpected, it doesn’t just activate the areas of our brain dedicated to processing scents. Surprisingly, it also triggers activity in our visual cortex – the part of the brain responsible for processing what we see – even if there’s nothing visually present.

“The olfactory brain thus has a completely unique way of processing smells and it is about whether the smells are expected or not. The sense of smell warns us of smells that we had not expected, and engages the visual brain, perhaps to be able to see what it is that smells,” said Professor Jonas Olofsson, co-author of the study.

This suggests that our brains are trying to create a more complete sensory picture when an unexpected smell arises. It’s as if our sense of smell alerts the visual system, saying “Hey, there’s something out there you might want to take a look at.”

Understanding brains prediction via smell

Let’s illustrate the above discussed mechanisms with some examples. Imagine walking into a bakery – the familiar scents of vanilla and sugar likely make your mouth water before you even see the treats.

This is your brain’s prediction system in action. You’ve learned to associate those smells with delicious baked goods, so your brain prepares you for the pleasant experience to come.

But what about a strange, burning smell? This unexpected scent disrupts your brain’s predictions. Suddenly you’re on high alert, eyes scanning for the source of the problem. Your nose has signaled “something’s not right,” triggering a heightened sense of awareness.

“We have all experienced that we react to when an unexpected smell appears, for example when we enter someone’s flat and encounter a new smell. Our research shows that the sense of smell is highly influenced by the cues from other senses, while the sense of sight and hearing are affected to a much lesser extent,” said Jonas Olofsson.

This highlights how our sense of smell works in tandem with our other senses and past experiences to create a continuous understanding of our surroundings.

Applications of smell prediction

In the world of VR, the integration of olfactory cues could significantly enrich user experiences. Until now, VR has predominantly focused on visual and auditory stimuli. However, incorporating smell, based on the predictive coding model, could create more immersive and realistic virtual environments.

For instance, a VR simulation of a forest could include not just the sights and sounds but also the earthy scent of moss and the freshness of pine, anticipated by the user’s brain, thereby enhancing the overall experience. This leap in sensory integration could revolutionize gaming, education, and even virtual tourism, making experiences more lifelike and engaging.

Beyond entertainment and education, the practical applications of these findings in smell training and rehabilitation are profound. Understanding that the sense of smell operates on predictions allows for the development of targeted therapies for individuals with impaired olfactory functions.

Developers could create tailored smell training programs aimed at retraining the brain’s ability to predict smells. This approach has the potential to restore or improve the sense of smell for those who have lost it through illness, injury, or as a part of aging. Improving someone’s sense of smell can greatly enhance their quality of life.

Study significance

Our noses seem designed to prioritize the unexpected. This makes sense from an evolutionary perspective – an unfamiliar scent could signal danger or a potential resource.

This research raises some fascinating questions. Could we improve our ability to predict smells through training and experience? Think about expert wine connoisseurs. Could their ability to discern a wine’s vintage by its aroma alone be a result of a finely-tuned smell prediction system? They’ve developed an extensive library of “smell expectations” through years of practice.

It’s something for scientists to continue exploring – and perhaps a fun experiment to try at home. Start paying closer attention to familiar smells and try guessing what they are without looking at the source. You might be surprised by how much your nose already knows.

The study is published in The Journal of Neuroscience.

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