Smells can be surprisingly emotive. A passing scent of perfume might remind you of an old friend, or the aroma of dinner cooking on the stove might take you back to your grandmothers’ cooking. In a new study, reported Progress in Neurobiology, researchers show how human evolution and the brain's wiring may help to explain how smells manage to spark such strong memories.
Scientists at Northwestern University looked at the different networks that hook up our primary sensory areas - sight, sound, touch, and smell - to the hippocampus, a complex brain structure involved in emotions and memory formation. They discovered that the hippocampus has a significantly stronger connection to the sensory system used for smelling, the olfactory system. They argue that this supercharged direct-line between the olfactory system and the hippocampus might help to explain why smells can elicit such a strong emotional response in people.
According to the researchers, this sensory autobahn between the olfactory system and the hippocampus is most likely a reflection of how the brain architecture underwent some subtle rewiring while it was evolving.
“During evolution, humans experienced a profound expansion of the neocortex that re-organized access to memory networks,” Christina Zelano, study author and assistant professor of neurology at Northwestern University Feinberg School of Medicine, said in a statement.
“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,” explains Zelano.
Considering the importance of smell on our emotions, the researchers also highlight how a smell of loss can greatly impact the quality of life. A solid amount of research has even linked the loss of smell with depression
This is of particular recent concern since COVID-19 is known to be closely associated with a loss of smell, aka asomnia. In fact, the loss of smell is one of the most commonly reported side-effects of long-COVID and can often endure for weeks, if not months, after the initial infection. This new study did not specifically look at asomnia related to COVID-19, but it could provide some clues into how the infection, as well the lingering effects of long-COVID, may have a profound impact on peoples' quality of life.
"The COVID-19 epidemic has brought a renewed focus and urgency to olfactory research. While our study doesn't address COVID smell loss directly, it does speak to an important aspect of why olfaction is important to our lives: smells are a profound part of memory, and odors connect us to especially important memories in our lives, often connected to loved ones," adds Zelano.