It’s likely that at some time in your life, a certain smell, whether the earthy aroma of freshly cut grass or the unmistakable fragrance of your grandparents’ house, triggered a powerful and strangely detailed memory. Well, there’s a biological reason for that. Unlike our four other best-known senses, whose electrical impulses are first sent to our thalamus before being sent to appropriate areas for memory, such as the hippocampus, our sense of smell takes a different route. Instead of being sent to the thalamus, scents go straight to the smell center known as the olfactory bulb. The fact that this bulb is directly connected to the hippocampus and the amygdala (which is responsible for emotional processing) is likely why smell evokes such powerful memories compared to our other senses. These memories can be extremely distinct, and they’re often linked to our childhood, likely because they were first stored when we experienced the scent at a young age.
According to a 2017 study, a part of the olfactory bulb known as the piriform cortex is what allows certain smells to be deposited in our long-term memory, though this cortex requires other parts of the brain to pull this off. The olfactory bulb essentially consults our orbitofrontal cortex, an area of the brain responsible for higher-level taste and smell functions, about whether a smell should be stored in long-term memory.
Companies are very aware that smell can be a powerful reminder of memory and emotion, which is why some of them have even trademarked certain scents (yes, you can do that). Verizon, for example, owns the rights to its “flowery musk scent” used in its stores, and olfactive branding companies work with clients like Nike to leverage the power of smell. Because when it comes to unlocking human emotions and memories, it might be the strongest sense we have.
Humans can smell fear
Human communication is usually associated with sight, hearing, and touch. But our sense of smell also plays an unrecognized role in how we interact, and several scientific studies have discovered a latent human ability to detect chemical signals in human sweat. One study in 2008collected sweat from novice skydivers about to jump out of a plane, as well as sweat from the same participants when they were running on a treadmill. Then, another batch of participants sniffed the “fear” and “non-fear” sweat pads while inside a brain scanner. Although the subjects could not consciously differentiate between the smells of the two pads, the scanners detected increased activity in the amygdala, the region of the brain associated with emotional processing, when sniffing the “fear” sweat pad. Many other studies have since reproduced similar conclusions, but scientists remain stumped as to what chemical is triggering this response. While some people have what’s called a “vomeronasal organ,” which in other animals detects the scent of prey and sex pheromones, the organ is vestigial in humans (meaning it once played a role in our primate past but is no longer functional, sort of like the appendix). Despite this, some scientists argue that the ability to sense chemosignals provides significant advantages for animals that thrive in groups (like humans), and could also explain the mostly noncommunicative bond between a mother and newborn. In other words, there’s still some lingering mystery around what the nose knows.
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