Freshly baked cookies, clean laundry, good coffee – each of these aromas has the power to trigger specific memories that seem to transport us to a different place and time. But it's not just pleasant aromas that have this effect.
"Maybe you went to a restaurant and ordered a dish and then suffered from food poisoning. You'll develop an aversive memory to the scent of that dish," says Omar Danoun, M.D., a neurologist at Henry Ford Health.
It turns out that smells trigger powerful emotional memories largely because the brain regions that process smells, memories and emotions are intimately connected.
How Smell Happens
Most people rely more on sight than smell throughout the day, so why is our sense of smell better at conjuring memories and emotions? According to Dr. Danoun, the power lies in the architecture of the brain. Our other senses travel through the thalamus (the communication hub of the brain). But smell goes directly to the brain’s emotional center, including the areas responsible for processing emotion and memory.
Here's how it works: A scent in the form of a chemical particle travels through the nose and into the olfactory bulb in the brain, where it's processed into a readable scent. From there, brain cells carry information about the smell to the almond-shaped region of the brain that processes emotions (the amygdala), and then to the learning and memory center of the brain (the hippocampus).
"So, it makes sense that our individual human experiences shape how we perceive smells and scents," Dr. Danoun says. "That's why people often connect the scents of their mother's home cooking with positive emotions like warmth, love and nurturing."
But the smells that comfort one person can reawaken a past trauma for another. A person who was abused by a relative who served up hot dogs at family events, for example, might have a hard time stomaching the smell of a ballpark frank. Scientists call these experiences odor-invoked autobiographical memories.
Losing Your Sense Of Smell
Human beings have tremendous smell potential. Research suggests that our brains have 1,000 different receptors for scents. But what happens when aging, a brain injury or infection with COVID-19 hijacks your sense of smell? It's complicated.
"Since smell and memory are so closely linked, losing your sense of smell can affect your memory," Dr. Danoun says. In fact, the relationship between smell and memory also plays a role in memory-related health issues. A loss of smell can be an early sign of Alzheimer's disease and Parkinson's disease, and it can contribute to depression.
"If you lose your sense of smell, you also lose the connection to certain memories," Dr. Danoun explains. "So you're not getting the triggers from smell that flood the brain with feel-good hormones like dopamine."
Recovering A Lost Sense Of Smell
It's true that people lose their sense of smell with age and health conditions, including COVID-19. But all hope is not lost. With something called olfactory training, you can coax your brain to recover those lost connections to smell.
"Olfactory training teaches the brain to remake the connections back to specific scents," Dr. Danoun says. You can do it yourself by exposing your nose to four different pleasing scents during each session — things like lemon, oregano, lavender and cinnamon. Identify the first scent and then let the aroma waft through your nose for 25 seconds. Allow the brain to process that scent for a full minute before moving on to the next.
If you still can't make out the smell, don't fret. "Over time, your brain will make the connections," Dr. Danoun says. "It may take a few weeks or even months, but if you're persistent, your brain's ability to sense them will usually come back." You may need up to three months with the first batch of four scents before you’re ready to move on to the next set.
Still struggling to sense scents? Make an appointment with your primary care provider to rule out other causes. Infections and uncontrolled allergies may impact what you can smell. And if you lost your sense of smell after COVID-19 infection, be patient with olfactory training: It can take up to a year before you recover your sense of smell.
"Smell is a muscle that you can develop the same as you develop other muscles and other skills," Dr. Danoun says. "The more you use your sense of smell, the stronger it gets."
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Dr. Omar Danoun is a neurologist with Henry Ford Health. He sees patients at Henry Ford Hospital in Detroit and Henry Ford Medical Center in Taylor.