Per a recently published study in Nature Communication, a team of scientists at the University of Toronto have identified a mechanism that allows the brain to recreate vivid sensory experiences from memory.
"Our findings demonstrate for the first time how smells we've encountered in our lives are recreated in memory," said Afif Aqrabawi, a Ph.D. candidate in the Department of Cell & Systems Biology in the Faculty of Arts & Science at the University of Toronto, and lead author of the study.
The AON and Our Sense of Smell
In an effort to explore the connection between memory and olfaction, Aqrabawi and graduate supervisor professor Junchul Kim began by examining a region of the brain known as the anterior olfactory nucleus (AON) – a portion of the brain that plays a crucial role in our sense of smell. Through examining structures and function of the AON in mice, the researchers were able to uncover a previously unknown neural pathway between the hippocampus and the AON, which they believed was crucial to memories and scent.
"[Mice] prefer to spend more time smelling a new odor than one that's familiar to them," said Aqrabawi. "When they lose this preference, it's implied they no longer remember the smell even though they have sniffed it before, so they continue to smell something as if for the first time."
To test the functions of the AON, Aqrabawi and Kim designed a set of tests to exploit the preference of mice to sniff new odors. In a set of mice, the researchers disconnected the neural pathway between the hippocampus and AON and compared them to mice with intact connections. They found that mice with a disconnected pathway sniffed previously smelled odors for longer periods of time, while the other mice didn’t.
Detecting Alzheimer’s through Scent
In conclusion of this study, the researchers believe that with a better understanding of neural circuits that they can understand the early stages of Alzheimer’s and the onset of the disease. In other studies, it has already been documented that the AON is involved with Alzheimer's and is among the earliest sites of neurodegeneration. With this research and further studies, the scientists believe that better tests for detecting Alzheimer’s through scent can be created.
"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," said Kim. "Such tests might be more sensitive to detecting problems than if patients were prompted to remember an odor itself. The motivation to develop them is high due to their quick, cheap, and easy administration."