How Smells Trigger Certain Memories (And What That Means for Early Alzheimer’s Detection)
We’ve all been there: We get a whiff of something familiar — a perfume, a favorite meal, an old bookstore — and suddenly we can remember things and events that were hidden in our memories for years, perhaps even decades. But how exactly are these “odour memories” formed, and could our ability to retrieve them (or not) be an indication of a bigger concern?
Previous studies have revealed that changes to one’s sense of smell could be an early indicator of Alzheinmer’s disease. But now, scientists have gained new insights into just how our senses, particularly our sense of smell, are represented in memory, and how this connection can potentially help explain why the loss of smell is considered an early sign in Alzheimer’s disease diagnosis.
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In July of 2018, a group of neurobiologists at the University of Toronto sought to better understand how the anterior olfactory nucleus, also known as the AON — the part of the brain that processes smell-related information — receives cues from the hippocampus — the part of the brain responsible for short-term, long-term and spatial memory.
Lead author Afif Aqrabawi, a PhD candidate in the neurobiology department at the University of Toronto noted that their findings “demonstrate for the first time how smells we’ve encountered in our lives are recreated in memory. In other words, we’ve discovered how you are able to remember the smell of your grandma’s apple pie when walking into her kitchen.”
The Relationship Between Smell and Memory
Together with Professor Junchul Kim from the psychology department, Mr. Aqrabawi observed a strong relationship between recognizing odors and sharpness of memory in their study of mice.
Interestingly, in the case of cognitive decline or dementia, the AON is one of the first areas of the brain to be compromised. This likely explains why Alzheimer’s patients, in particular, forget when and where they smelled odors before.
Professor Kim said, “Given the early degeneration of the AON in Alzheimer’s disease, our study suggests that the odor deficits experienced by patients involve difficulties remembering the ‘when’ and ‘where’ odours were encountered. Such tests might be more sensitive to detecting problems than if patients were prompted to remember an odour itself. The motivation to develop them is high due to their quick, cheap, and easy administration.”
What this Research Means for Alzheimer’s Detection
The researchers found a disconnected pathway in Alzheimer’s patients who sniffed previously smelled odors longer than new smells. It’s common to spend more time smelling a new odor than a familiar one, but not for people who have early onset of Alzheimer’s disease and patients did not recognize these odors that they previously smelled.
Smell tests are now being used in detecting the early onset of Alzheimer’s disease and the loss of the ability to smell, has become recognized as an early symptom of Alzheimer’s disease. The research team is working on developing more sensitive smell tests, in order to help prompt patients to remember an odor.
Afif J. Aqrabawi, Jun Chul Kim. Hippocampal projections to the anterior olfactory nucleus differentially convey spatiotemporal information during episodic odour memory. Nature Communications, 2018; 9 (1) DOI: 10.1038/s41467-018-05131-6