This is why smells and memories have such a strong connection

Smell is perhaps the most underappreciated of the five senses. True, it isn’t quite as glamorous as our sense of sight, and may not be as useful as the ability to hear. Yet, our noses color and fill in so many of the smaller details of our lives. That new car smell. The creeping aroma of a nearly finished dinner emanating from the kitchen. That trademark movie theater smell of popcorn mixed with way too much butter.

Such smelly cues often spark something unexpected in our memories. How many times have you smelled something that reminded you of a past event or particular memory? It’s a universal human experience, made famous by French writer Marcel Proust’s legendary seven-volume story In Search of Lost Time. In the novel, the smell and taste of a madeleine (French cookie) evoke an intense wave of long-forgotten childhood memories in the protagonist.

The close connection between smell and memory is undeniable, but up until now the physical and neural reasons for this association have remained a mystery. A groundbreaking new study just released by Northwestern University is changing all that.

This new research shows that the brain’s memory center (the hippocampus) is directly connected to the body’s olfactory system (the sensory system that facilitates the sense of smell) in a way unlike sight, taste, hearing, etc. Study authors even go so far as to call the pathway between the nose and the hippocampus a “superhighway.”

Just like pretty much everything else about our bodies, the team at Northwestern says evolution played a big role in the close modern relationship between smell and memory. 

“During evolution, humans experienced a profound expansion of the neocortex that re-organized access to memory networks,” says lead study investigator Christina Zelano, assistant professor of neurology at Northwestern University Feinberg School of Medicine. “Vision, hearing and touch all re-routed in the brain as the neocortex expanded, connecting with the hippocampus through an intermediary–association cortex–rather than directly. Our data suggests olfaction did not undergo this re-routing, and instead retained direct access to the hippocampus.”

So, while sights, sounds, and sensations have to pass through a few intermediaries, odors have a direct line to the hippocampus. 

“This has been an enduring mystery of human experience. Nearly everyone has been transported by a whiff of an odor to another time and place, an experience that sights or sounds rarely evoke. Yet, we haven’t known why. The study found the olfactory parts of the brain connect more strongly to the memory parts than other senses. This is a major piece of the puzzle, a striking finding in humans. We believe our results will help future research solve this mystery,” Zelano explains.

The exact reasons why the olfactory system evolved to connect so closely with the hippocampus remain up for debate. Perhaps it was more advantageous for early humans to pick up on learned danger cues via odors than other senses. For example, one often smells a fire before seeing it, and associating a particular odor with a poisonous plant or mushroom is probably easier than memorizing colors, shapes, or patterns.

Regardless of the evolutionary reasons, the fact remains that our sense of smell is a big part of how we interact with and learn about the world around us.

“Smells are a profound part of memory, and odors connect us to especially important memories in our lives, often connected to loved ones. The smell of fresh chopped parsley may evoke a grandmother’s cooking, or a whiff of a cigar may evoke a grandfather’s presence. Odors connect us to important memories that transport us back to the presence of those people,” Zelano adds.

The full study can be found here, published in Progress in Neurobiology.