The sense of smell is very powerful regarding memories and events. Smelling a favorite food can bring back vivid memories of when you first had it.
The brain processes odors and scents in much the same way as it handles experiences and learning. A recent study by researchers at the University of Toronto shows that smell and memory processing are intertwined in the brain and could lead to better diagnostic tests for Alzheimer’s.
The study, which is published in the journal Nature Communications, explains where in the brain memory and smell are connected. The amygdala, which is a small almond-shaped part of the brain that processes sensory input, sits quite near the hippocampus where memories are stored. Together, sensory information and our experiences create episodic memories. We remember cooking S’mores over a campfire because not only the event is stored in the brain, the sensory stimuli is encoded as well. The smell of wood, melting chocolate and burnt marshmallows are firmly entrenched in the memory banks.
Information about space and time is also processed by a specific part of the brain called the anterior olfactory nucleus. It’s part of the mechanism behind Alzheimer’s disease. Patients with AD often forget what period of time they are in, thinking that they are back in childhood or a person they know is unrecognizable to them. Having scent and spatiotemporal information so closely connected in the brain might be an avenue for research into Alzheimer’s.
Study co-author Afif Aqrabawi is a Ph.D. candidate in the Department of Cell & Systems Biology at the University of Toronto in Canada. Graduate supervisor Jun Chul Kim, a professor in the Department of Psychology at the University of Toronto also worked on experiments in mice that found a previously undiscovered neural pathway between the AON and the hippocampus. Agrabawi explained, "When these elements combine, a what-when-where memory is formed [...] This is why, for example, you might have the ability to remember the smell of a lover's perfume (the what) when you reminisce about your first kiss (the when and where)." Professor Kim added, 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' odors were encountered."
In the study, the researchers disrupted the pathway in the lab mice. Typical mice will prefer to seek out new odors to sniff rather than smelling scents that are familiar to them. When the mice were altered, and this pathway was not present, the mice showed more of a preference for familiar smells. The mice didn’t seem to remember familiar scents of food or treats and acted as if every smell is new to them.
Many patients with Alzheimer’s also have difficulty smelling certain odors, and that has led to a “sniff test” for some patients. The decline in the ability to smell happens early in the disease, and the new information uncovered in the work at the University of Toronto could enhance those tests as a useful early detector of possible dementia. Check out the video below for more information.