New Research Explains Why Scent Triggers Such Powerful Memories

Certain smells, both good and bad, have a way of transporting us back to specific moments in our lives. Likely, you can even call one to mind right now.

A new study published in Progress in Neurobiology explores the power of scent in triggering memories, suggesting this ability comes from the connection between the olfactory system and the hippocampus in the brain.

As part of the limbic system, the hippocampus serves the most primitive aspects of our brain, like memory, pleasure, pain, and motivation. It plays a critical role in our ability to form new memories and acts as a sort of temporary storage and command center for their organization.

A better understanding of the olfactory system could help us better understand broader brain dysfunction and advance intervention and treatment.

What the Study Shows

The new study set out to better understand the human olfactory system and its connection to memory. Lead researcher Christina Zelano, PhD, and the study's team of researchers set out to better understand the profound role our sense of smell has in connecting us to our memories.

With the help of neuroimaging and intracranial electrophysiology, researchers were able to directly compare the ways in which the hippocampus functions across human sensory systems. This comparison revealed that, at rest, the olfactory system is more strongly connected to the hippocampus networks than the other systems of sight, sound, taste and touch.

The Scent-Brain Connection

Evolutionarily speaking, any animal's sense of smell is a critical survival tool, Zelano says. We are constantly monitoring the air around us with every breath, sending information directly to our nervous system.

Zelano describes this system as both fascinating and under-appreciated. "It is our oldest sensory system, evolutionarily speaking, and the one located deepest in our brains," she says.

"It is a complex system, with many parallel paths delivering odor information simultaneously to many brain areas milliseconds after we sniff... This powerful sensory system is critical to our human experience. Yet it is perhaps the most poorly understood system compared to other human sensory systems," says Zelano.

Our sense of smell is also profoundly connected to memory. Studies have shown that odor serves as a stronger trigger than any other sensory cue for recalling personally meaningful memories.

"Smell and emotion intertwine and can be saved in the brain’s software for years," says psychiatrist Leela Magavi, MD. "Scents that soothed children can continue to alleviate stress and anxiety for the entirety of adulthood. Scents that triggered anger and sadness can continue to result in negative emotions for years to come."

"We can also use our sense of smell to very quickly assess complex aspects of our environment: good and bad smells can guide where we go, what we eat, who we like to be with, where we are comfortable or ill-at-ease," she says. "And memory is a critical part of all of these decisions and more."

Smell Loss and Brain Dysfunction

With the COVID-19 pandemic, smell loss has become an epidemic of its own. It's been estimated that, of people with mild cases of COVID-19, about 86% lose some or all of their ability to smell. Within six months, 95% of those people will have regained their sense of smell.

Beyond being recognized as a symptom of COVID-19, smell loss is highly correlated with depression and can have immense negative effects on quality of life, Zelano points out.

As we age, our sense of smell gradually begins to fade, which directly impacts our ability to taste and enjoy food. An inability to smell can also affect our ability to sense danger, like failing to notice that something is burning.

At the same time, smell loss appears to implicate broader brain dysfunction and even neurodegenerative diseases. Dysfunction in the olfactory system is common and serves as an early symptom of conditions like Alzheimer's and Parkinson's diseases. However, Zelano is careful to point out that smell loss is not indicative of having either of those diseases in the future.

A better understanding of conditions like these calls for a better understanding of the facets of the olfactory system and how odors affect the human brain—for example, its aptitude for evoking vivid memory.

"By advancing the basic neuroscience of olfaction... we hope that this will lead to better interventions and treatments of smell loss, and perhaps even other neurological diseases," Zelano says. 

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