These are fragrances that evoke a mood or a place. Olfactory memory refers to the recollection of smells. The delicious scent of baking bread wafting out from the open doors of a nearby bakery can act like a time portal, instantly sweeping you from a busy street in New York to a tiny cafe in Paris that you visited years ago. Scent particles, in general, can revive memories that have been long forgotten. So many of these odor-driven memories may be childhood memories because those years are when we experience most smells for the first time. But why do smells sometimes trigger powerful memories, especially emotional ones? The short answer is that the brain regions that juggle smells, memories and emotions are very much intertwined. In fact, the way that your sense of smell is wired to your brain is unique among your senses.
When you see, hear, touch, or taste something, that sensory information first heads to the thalamus, which acts as your brain's relay station. The thalamus then sends that information to the relevant brain areas, including the hippocampus, which is responsible for memory, and the amygdala, which does the emotional processing.
But with smells, it's different. Scents bypass the thalamus and go straight to the brain's smell center, known as the olfactory bulb. The olfactory bulb is directly connected to the amygdala and hippocampus, which might explain why the smell of something can so immediately trigger a detailed memory or even intense emotion.
That results in an intimate connection between emotions, memories and scents. This is why memories triggered by scents as opposed to other senses are "experienced as more emotional and more evocative," said Rachel Herz, an adjunct assistant professor of psychiatry and human behavior at Brown University in Rhode Island and author of the book "The Scent of Desire" (Harper Perennial, 2018). Scents are "really special" because "they can bring back memories that might otherwise never be recalled," Herz said. Typically, when a person smells something that's connected to a meaningful event in their past, they will first have an emotional response to the sensation and then a memory might follow. But sometimes, the memory won't ever resurface; the person might feel the emotion of something that happened in the past but won't remember what they experienced, Herz said. "And this is unlike any of our other sensory experiences," she added.
In November 2017, scientists discovered something even wilder about the processes that make odor-linked memories so vivid: The memories may be saved in a part of the olfactory bulb itself. The part responsible is a complex structure called the piriform cortex. The piriform cortex connects to all sorts of places in the brain, including a higher-level structure called the orbitofrontal cortex. This structure is generally responsible for making judgments about sensory input: this sweater feels good, touch it again; that week-old Chinese food smells off, don't eat it. The researchers tried using the same impulses to stimulate this region, and sure enough, it triggered memory changes in the piriform cortex. So not only does your brain's smell center connect right to its memory center, but it also stores long-term memories in-house. Go ahead, take a nice long whiff of that old bottle of perfume or the paperbacks in that used bookstore. The memories that come flooding back to you are a happy side effect of the way your brain is wired.