Have you ever noticed that certain smells have the ability to hit you with a rush of memories? Why is it that freshly-baked cookies can transport you back to Grandma’s house, while even the faintest hint of tequila brings back the embarrassment and regret from that time you partied a little too hard?

The overlap between smell and memory isn’t just a coincidence. Their relationship is actually hard-wired into the structure of our brains.

To explain this phenomenon, we have to understand how the sense of smell is processed by the brain. What is “smell” anyway?

Anything that has a scent gives off tiny chemical particles known as odorant molecules. These travel through the nose and into the nasal cavity, where they eventually land in an area called the olfactory epithelium. Here, there are a bunch of neurons (the cells of the nervous system) that contain specialized smell receptors.

When odorant molecules bind to these receptors, the actual signal transduction of smell begins. In simpler terms, this binding process initiates a series of chemical reactions that relay the “smell signal” to the brain.

How's the brain able to tell different scents apart? It has to do with the characteristics of the odorant molecule and the properties of the olfactory receptor neuron it binds to.

Depending on the odorant molecule, different responses will occur in the neuron upon binding. Each unique response is interpreted as a unique smell by the brain.

In the human brain, smell is processed in two areas. The first area is in a region of the frontal cortex, and it's here that we consciously recognize smells for what they are.

The second area is the amygdala, a structure that's part of the limbic system. This system is responsible for our perception of emotion and memory. The connection between sense of smell and the limbic system is responsible for our association between specific smells and individual memories, especially memories that are emotionally-charged.

When we encode memories, we also encode the sensory information that goes with them, such as scents. Because the smell and memory processing pathways are directly linked, it's believed that experiencing a certain smell can directly trigger the memory associated with it.

The next time you catch a whiff that conjures up memories from your childhood, your favorite holiday, or even a time you’d rather forget, you can thank the organization of your brain for the sudden blast from the past. Smells like nostalgia to me.