February 9, 2020
How Olfactory Performance Sniffs Out Signs of Cognitive Decline
The silhoutte of a human profileSource: Pexels
You’re only as young as your nose, err… What?
More specifically, researchers have been investigating the link between odor identification and how it may be an indicator of cognitive health later in life.
A 2013 Chemical Senses study evaluated 220 participants around the age of 72 years old with mild cognitive impairment and found severe hyposmia – a reduced sense of smell – correlated with “significantly poor verbal and visual memory performance.” Participants with severe hyposmia also displayed attention and executive function difficulties, in addition to slower processing speeds.
Whereas participants without hyposmia had higher performance scores after the researchers adjusted for variables including age, sex, education, and other cognitive performance scores.
“These findings suggest that olfactory impairment might be more closely associated with memory loss compared with other aspects of cognitive functioning in mild cognitive impairment subjects,” the study concluded.
Before diving any further, let’s take a moment to explore how smell works through the olfactory system.
The Olfactory System
Where Does Our Sense of Smell Come From?
A young woman takes a hearty sniff of a sunflowerSource: Pexels
First, take a long, deep whiff. What do you smell? Is it a candle? Perfume? Coffee on your desk? Dirty laundry in the corner of your room? Your dog?
Whatever the smell may be, the specialized chemosensory cells called “olfactory sensory neurons” first have to travel from a small patch high inside your nose to your brain, says the National Institute on Deafness and Other Communication Disorders.
These olfactory sensory neurons are triggered by microscopic molecules from our surroundings. Then, the neurons send signals to your brain to decipher what the molecules are.
Our nose isn’t the only way our brain receives these signals, either. There are two pathways for olfactory sensory neurons to reach the brain: one pathway through the nostrils, and the other through a channel that connects the roof of your mouth to your nose.
The NIDCD gives the example of chewing food, which communicates the aroma through the olfactory sensory neurons in the second channel.
“If the [second] channel is blocked, such as when your nose is stuffed up by a cold or flu, odors can’t reach the sensory cells that are stimulated by smells,” the NIDCD explains. “As a result, you lose much of your ability to enjoy a food’s flavor. In this way, your senses of smell and taste work closely together.”
Additionally, olfactory sensory neurons allow us to distinguish familiar scents and give us the ability to taste food.
“Without smell, foods tend to taste bland and have little or no flavor,” the NIDCD says. “Some people who go to the doctor because they think they’ve lost their sense of taste are surprised to learn that they’ve lost their sense of smell instead.”
Olfactory and Aging
Over the years, researchers have unveiled a body of evidence supporting the idea that olfactory function correlates with cognitive health later in life but research on the general population is rare, says a 2018 Journal of Alzheimer’s Disease study.
2,640 participants, 48 percent of them male and between the ages of 68 to 75 years old, were given the “Sniffin’ Sticks Screening Test.” The results were measured on a 12 point scale ranging from anosmic (loss of smell), hyposmic (partial loss of smell), and normosmic (‘normal’ sense of smell).
Although women tended to score better on the Sniffin’ Sticks Screening Test, the study revealed no gender association with olfactory performance.
However, those who anosmic showed “the worst cognitive performance,” whereas normosmic participants displayed “the best cognitive performance.”
Once again, the study concluded that olfactory dysfunction could be an indicator of cognitive decline and dementia for senior citizens.
A 2017 Neuroscience Bulletin review also discusses how olfactory dysfunction is common among those diagnosed with Parkinson’s Disease and “often predates the diagnosis by years.”
But How Can We Know For Sure?
While multiple studies have shown correlations between olfactory performance and cognitive health, there’s only one way to know for sure how accurate the correlation is: we have to peek inside the brain.
So, researchers did.
A NeuroImage study was published earlier this month that examined the gray matter volumes in the core olfactory and memory areas associated with olfactory performance.
The 422 participants were at least 60-years-old and didn’t have neurodegenerative conditions. Their episodic (personal) and semantic (factual) odor memory was tested along with their episodic and semantic verbal memory while undergoing an MRI.
“In sum, our data provide evidence that differences in olfactory semantic memory performance, as measured by odor identification, are associated with distinct patterns of differences in regional gray matter volume,” the study concluded, thus demonstrating region-specific data of the link between olfactory performance and cognitive health.
Your nose knows best – and it just might know the state of your cognitive health.
While olfactory performance can help neurologist whiff out signs of cognitive decline sooner than later, it’s still worth mentioning there are other causes of hyposmia and anosmia.
For example, three other main causes of olfactory dysfunction are trauma, viral infections, and nasal conditions, says a 2012 German Society Current Topics in Otorhinolaryngology – Head and Neck Surgery review.
However, if you or a loved one are over the age of 60 and think something’s going foul with your sense of smell, it’s important to schedule an appointment with a neurologist.
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