There was a time in the evolution of humans when a powerful sense of smell was an important survival skill. Early humans depended on their sense of smell to warn them of danger from a predator or to lead them to food.

For modern humans, the sense of smell is underused, underdeveloped, and underappreciated. Our modern world is relatively sterile and free of odor compared with the old world. That may be why our sense of smell starts to fall off a cliff after age 60. But some very important research suggests that stimulating your sense of smell may be important for mind health.

Smell and the brain

In August 2023, a study published in the journal Frontiers in Neuroscience demonstrated a strong association between exposure to new odors and improved memory. The researchers call this type of exposure olfactory enrichment. The word olfactory comes from the Latin word for smell, olfacere. The nerve that carries smell from the nose to the brain is called the olfactory nerve.

In the study, researchers from the University of California Irvine’s Center for the Neurobiology of Learning and Memory randomly exposed 43 men and women between the ages of 60 to 85 to two hours of aroma from different essential oils while sleeping (olfactory enrichment) or to an odorless vaporizer (the control group). None of the people in the study had problems with their memory or thinking (cognitive skills).

A battery of memory and cognitive tests and MRI brain imaging were done at the start of the study and six months later at the end of the study.

The results were mind boggling. The olfactory-enrichment group improved their memory and cognitive skills by 226 percent, while the control group’s scores remained unchanged. The olfactory enriched group also had significantly increased activity in memory and learning areas of the brain called the limbic system seen on brain imaging.

The new study builds on a growing body of evidence that shows how closely the sense of smell is linked to thinking and memory. A 2013 study found that olfactory enrichment improved verbal fluency in Parkinson’s disease. A 2018 study found it improved puzzle solving (Sudoku), verbal function, and decreased symptoms of depression. In 2021, three to six months of olfactory stimulation improved cognitive abilities in people with early dementia.

How does smell stimulate the brain?

Have you ever noticed that a certain smell triggers a strong memory, like the smell of baking bread taking you back to a childhood memory of your grandmother’s kitchen? The reason is that the olfactory nerve is the only sensory nerve that goes directly to your brain’s limbic system, where memories are made and stored.

The connection between the nose and the memory centers of the brain is like a two-lane highway. Smells trigger memories going one way, while on the other side of the highway, memory loss may reduce the sense of smell from your nose. In fact, loss of smell is a strong predictor of age-related memory loss, minimal cognitive impairment, and dementia. It may also be the first sign of Parkinson’s disease and has been linked to brain disorders including schizophrenia, multiple sclerosis, and brain tumors.

When your limbic system is exposed to strong or new odors, your brain cells make new connections to recognize and save those smells in your memory bank. This process is called brain plasticity or connectivity. Think of these connections as accessory roads around highways. Connectivity builds new areas of active brain tissue. These connections can be used for increasing your sense of smell, but also for increasing your cognitive abilities, memory, learning ability, and speed of thought.

The sommelier experience

A good example of the untapped potential of olfactory stimulation is the training of wine experts called sommeliers. A master sommelier must be able to identify by smell and taste the grape type, country, region, year (vintage), and quality of 75 percent or more of all wines. Sommeliers also use taste, but about 80 percent of taste is due to smell. Without smell, the only tastes humans can identify are sweet, bitter, sour, or salty.

In a study of sommelier students who were exposed to dozens of wine odors and tastes during 18 months of study, brain imaging studies after training found significant increases in the size of the olfactory nerve and the size of a critical memory centers of the brain compared with before training.

Other benefits of olfactory enrichment

Using olfactory stimulation to prevent or treat loss of smell is now an accepted medical therapy for anosmia, the loss of smell. A recent example is anosmia from COVID-19. Olfactory training involves frequent stimulation with essential oils like eucalyptus, lemon, rose, or clove. According to a recent review, olfactory training has been the best treatment for COVID anosmia, more effective than nasal sprays or oral steroids. Olfactory stimulation studies have demonstrated improvements or return of smell in many other conditions that cause anosmia, including head trauma, infections, and Parkinson’s disease.

Another benefit is improved sleep. Several studies, including the most recent study, have found a significant improvement in sleep time and quality. Previous studies have found that olfactory enrichment at night deepens slow-wave sleep, which is the most refreshing type of sleep.

Olfactory enrichment versus aromatherapy

Olfactory enrichment, olfactory training, and aromatherapy all use essential oils. These oils are extracted from aromatic plants. It takes many pounds of a plant to get a small bottle of essential oil. The molecules of fragrance released from an essential oil are active and carry a strong aromatic odor. There are dozens of these oils, but the most popular include rose, orange, eucalyptus, lemon, peppermint, rosemary, and lavender.

Aromatherapy as a folk medicine has a long history, dating back to ancient Greece and earlier. Today, according to the National Institutes of Health, aromatherapy is used as therapy to improve both mental and physical health. A review from Johns Hopkins University notes there has been “a lot of buzz” lately, and some positive research for treating anxiety, pain, depression, sleep, and nausea. But, aromatherapy is not medicine, so it is not controlled by the FDA.

If you want to try aromatherapy, use oils that are pure, have the Latin name and purity on the label, and are sold in dark, colored glass to protect quality. Aromatherapy is often used along with other alternative therapies like massage and acupuncture. Like olfactory enrichment, aromatherapy can be given through a diffuser, but it can also be used by sniffing a diluted solution or by rubbing the oil during a massage.

What to do

Unlike aromatherapy, which proposes specific benefits for different oils, researchers using oils for enrichment or training believe it is the effect of any strong and stimulating odor on the limbic system that is important. They choose their oils based on a variety of pleasant odors that are more likely to be used repeatedly without any unpleasant reactions. The key is variety and frequency.

For now, olfactory enrichment is available only in clinical research trials, but that may be changing soon. The same team that published the study in Frontiers in Neuroscience is working on a home essential oil diffuser that you can program with a variety of essential oils to go off for two hours when you are sleeping. It is called Memory Air.

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