We’ve made our way through the other four senses, and now it’s time to talk about the fifth and final sense: smell.
Smell may not immediately seem like the most compelling sense, but in a way, we saved the best for last. There is something special about smell: it has a unique link to memory and emotion, which no other sense has.
Have you ever smelled something that immediately called you back to a memory you’d nearly forgotten? Or, have you ever encountered a smell that affected your emotions, like the perfume of an ex-lover long after you broke up? It’s not just you: smells can have intense emotional effects on anyone, thanks to the way the sense gets processed in our brains.
Yet, how does a scent go from our noses to our emotions? Let’s take a look at this path from start to finish.
First, Smells Travel Through the Air
For us to smell something, there has to be something to smell. Just like there are sounds at times and silence at others, sometimes there are smells around us, and sometimes our environment smells neutral.
Of course, even when we can’t smell anything, smells are still available. They just might not be strong enough for us to detect. Animals with a better sense of smell than ours, like dogs, can detect scents where we find none.
Smells, when they travel through the air before reaching our noses, are simply molecules. Those molecules generally come from chemicals that are volatile—or, in other words, that evaporate easily. Some objects aren’t so volatile, so they don’t have much of a smell, because molecules from them don’t evaporate into the air quickly.
Those molecules float through the air and eventually make their way to our noses, where the process of smell really begins.
Next, Your Nose Decodes the Smell
Inside your nose are many olfactory receptors. Each of your olfactory receptors deals only with a short list of scents. But, put together, all of these receptors can easily decode just about any scent you come across.
Your olfactory receptors are contained inside the olfactory sensory neurons, which lie deep inside your nose. While most of your neurons are below the surface of your body, these neurons sit on the surface and interact with the air inside your nostrils. Your nervous system connects these neurons to your brain. Most smells interact with multiple olfactory receptors at once, so your brain can get a clear idea of what it is you’re smelling.
Before it reaches your nose, a smell isn’t really a smell. It’s just some molecules in the air. But when they get to your nose, those airborne molecules can be translated into something recognizable.
Finally, Your Brain Reacts with Feeling
As with our other senses, our understanding of exactly how smells get processed in the brain is somewhat limited. However, we do know some things about the brain that make our experience of scent unique among the senses.
From your olfactory sensory neurons, information about the scent you’ve encountered gets sent to the olfactory bulb in your brain. Your olfactory bulb is the only sensory processing center that’s located in your limbic system.
The limbic system is a particular part of the brain that’s heavily involved in memory, mood, and emotion. Memory and scent seem to have evolved in tandem, giving them a unique link that’s not shared by any other sense.
Of course, our other senses do play essential roles in our memories, too, but the links aren’t quite as strong, because those senses don’t get processed in the limbic system. Meanwhile, the relationship between scent and memory is so powerful that the loss of smell is often one of the first symptoms of Alzheimer’s.
Because of this link, people tend to have unique emotional reactions to smells, depending on their prior experiences with that smell. A scent that was present during a bad experience can put you in a bad mood. Meanwhile, one that was present during a happy memory can make you feel happy when you reencounter it.
Smells can also bring up nearly forgotten memories thanks to the olfactory bulb’s place in the limbic system. That’s why, sometimes, encountering a specific scent can trigger a memory that you otherwise wouldn’t have thought of. Each of our senses can have fascinating effects on our brains and behavior, but smell is far more emotional and memory-oriented than most.
However, just because it’s emotional doesn’t mean it can’t also trick us. Next, we’ll be looking at some common ways each of our senses plays tricks on our minds—stay tuned to learn more about how the five senses work!