Why do certain smells trigger powerful memories?

Have you ever smelled a flower and been suddenly flooded with a childhood memory or did a certain smell of curry remind you of your grandmother? A new study has now decoded why and how the brain does this.

The researchers show that in humans there is unique connectivity between the hippocampus in the brain which plays a major role in learning and memory and the olfactory system (the sensory system used for smelling).

Guangyu Zhou, from Northwestern University in Chicago, explains the process in detail in an email to The Hindu: “During evolution, primate brains (including humans) massively expanded, developing the neocortex. Due to this expansion, direct connections between sensory areas and the hippocampus also expanded…In our study, we compared how the olfactory system connects to the hippocampus with how other sensory areas (vision, hearing and touch) do. We found that olfaction had stronger functional connectivity with the hippocampus than these other sensory systems.” He is the first author of the study.

The team writes that this strong connectivity is like a superhighway from smell to the hippocampus and may be the reason why odours can powerfully elicit memories. The results were published in the journal Progress in Neurobiology.

“Another fascinating finding from our study is that with every inhale, connections to our brain’s memory centres strengthen. We found that the connectivity between the olfactory cortex and hippocampus changes rhythmically with natural breathing. This is interesting because it shows that something as fundamental and natural as breathing is intimately connected with how memory works in our brain,” says Christina Zelano, Assistant Professor in the Department of Neurology at Northwestern University and senior author of the study in an email to The Hindu.

The team hopes that this work will contribute to the development of treatments for smell dysfunction and loss which has gained special attention in the era of COVID-19.

“We plan to further investigate a special link between breathing rhythms and brain rhythms. Inhaling and exhaling, especially through your nose, generates rhythms that move through your brain and change how your brain works. We are interested in comparing nose breathing with mouth breathing, and better understanding how these respiratory rhythms affect the brain,” adds Guangyu Zhou.