Why an odour can transport our minds so quickly, much more so than a sight, sound or touch.
The parts of the brain responsible for smell and memory have a unique connectivity with each other, a study finds.
The results help explain why a smell, like that of cut grass, can so powerfully evoke a long-forgotten memory.
Dr Christina Zelano, study co-author, said:
“…smells are a profound part of memory, and odors connect us to especially important memories in our lives, often connected to loved ones.
The smell of fresh chopped parsley may evoke a grandmother’s cooking, or a whiff of a cigar may evoke a grandfather’s presence.
Odors connect us to important memories that transport us back to the presence of those people.”
The hippocampus — the area of the brain vital for memory — has direct access to the olfactory areas of the brain (those related to smell).
Other primary senses like vision, hearing and touch do not show the same strong connection with memory, the researchers found.
Dr Christina Zelano, study co-author, said:
“During evolution, humans experienced a profound expansion of the neocortex that re-organized access to memory networks.
Vision, hearing and touch all re-routed in the brain as the neocortex expanded, connecting with the hippocampus through an intermediary–association cortex–rather than directly.
Our data suggests olfaction did not undergo this re-routing, and instead retained direct access to the hippocampus.”
The study of brain scans and electrodes placed on the brain also found that the connectivity between memory and smell areas of the brain changes as people breathe in and out through their nose.
Dr Zelano said:
“This has been an enduring mystery of human experience.
Nearly everyone has been transported by a whiff of an odor to another time and place, an experience that sights or sounds rarely evoke.
Yet, we haven’t known why.
The study found the olfactory parts of the brain connect more strongly to the memory parts than other senses.
This is a major piece of the puzzle, a striking finding in humans.”
Loss of the sense of smell has become more of a focus as it is a common symptom of COVID.
Dr Zelano said:
“Most people who lose their smell to COVID regain it, but the time frame varies widely, and some have had what appears to be permanent loss.
Loss of the sense of smell is underestimated in its impact.
It has profound negative effects of quality of life, and many people underestimate that until they experience it.
Smell loss is highly correlated with depression and poor quality of life.”
The study was published in the journal Progress in Neurobiology (Zhou et al., 2021).
