You can track your sleep stages and heart rate variability to get a better understanding of your health. But the one sense with the most direct line to your memory is the one you have no number for — and the one you probably pay the least attention to.
Olfactory Decline
It might seem obvious that your ability to smell (just like every other sense) declines with age. But it’s also the one we tend to notice the least. In a nationally representative sample of American adults aged 57 to 85, 22% had measurable olfactory dysfunction. But only 12% of them recognized the decline in their smell. After the age of 80, 39% to over 75% have olfactory loss, depending on the sensitivity of the testing methods used.
People whose smell was intact reported it accurately, and people whose smell was impaired mostly did not know. You might notice when you have a stuffy nose and lose your sense of smell quickly. But when you gradually lose your olfactory function each year across decades, it’s not noticeable.
You Need to Train Your Smell
You need to stimulate your smell just like you stimulate your brain by learning new things, or your heart by going to the gym.
A study followed trainee London taxi drivers and a group of controls through three to four years of learning a city's layout. In the taxi driver group that passed, grey matter in the posterior hippocampus increased because they were learning and recalling something new.
The same results have been shown with smell. Researchers in Canada followed 12 sommelier students and 13 control students across 18 months of training, imaging both groups at intervals. Olfactory bulb volume increased in the sommelier students and did not change in the controls, and the right entorhinal cortex — part of the memory system, and the cortex the olfactory pathway feeds directly — thickened.
A few years later, Dr. Leon published a study that showed exposing older adults to rotating natural fragrances during sleep boosted memory performance by 226%.
By strengthening the memory center of the brain through smell, you can tolerate more damage before symptoms appear. This is called cognitive reserve, and it's why olfactory stimulation may be able to delay future cognitive decline or the likelihood of developing diseases like Alzheimer's.
What Else Does Olfactory Enrichment Do for the Brain?
We now understand that olfactory enrichment can physically change the structures in the brain related to memory. But what else can it do?
In a randomized trial, 91 adults aged 50 to 84, all with normal olfactory function at the outset, either trained twice daily with four scents for five months or, in the control group, completed a daily Sudoku puzzle. The group that had olfactory enrichment not only improved on verbal fluency and short-term memory, but also reported significantly higher general wellbeing and showed a greater decrease in depression scores than the controls.
Dr Leon reports similar findings from his own trials: participants reported sleeping better and feeling happier. In a study from another lab, participants said that they felt around six years younger.
The Bottom Line
Your sense of smell has probably already declined, and you almost certainly haven't noticed. This can have longstanding consequences on your memory, cognition, and overall brain health.
Memory Air was built to solve this problem by enriching the nose-to-brain connection. It’s a bedside device that delivers 40 distinct scents across the night. It runs while you sleep and asks nothing of you beyond going to bed.