Can Smell Training Improve Memory?

The loss of smell is often the first indication of future cognitive decline.

Reviewed by Abigail Fagan

Key points

• The olfactory nerve is the shortest cranial nerve.
• Research suggests smell training may help improve both cognitive and neuronal functions.
• Olfactory training could be an effective way to preserve memory and other cognitive functions in the elderly.

Searching for new ways to help my senior patients improve and maintain cognitive functions, I came across an interesting research study from the University of California Irvine (Woo, C. et al. 2023) that I want to share with my readers. The study explored the use of olfactory enrichment (smell training) at night to retain and improve cognitive abilities in healthy seniors.

What is smell training? It is a practice of exposing yourself to different scents on a regular basis to improve or restore your sense of smell. Olfactory training/retraining is mainly used nowadays to help COVID-19 patients. It is estimated that about 60% of COVID-19 patients lost some ability to taste or smell. But can smell training help with cognitive functions?

It sounded kind of crazy at first, but then I paused. Our nose has a direct connection to the brain through the olfactory nerve and olfactory bulb. The olfactory nerve is the shortest cranial nerve. It is the shortest distance from the outside world to our brain. It is only a few centimeters long; therefore smell training may make deep sense.

In the mentioned 2023 study, the subjects (43 men and women aged 60 to 85, with no diagnosis of cognitive impairment or dementia) were randomly assigned to an olfactory enrichment group or a control group. During the six months of the study duration, the subjects in the olfactory enrichment group were exposed to seven different scents of essential oils (rose, orange, eucalyptus, lemon, rosemary, and lavender) delivered by a diffuser at home, one scent per night for two hours and rotating the scents. The subjects were asked to turn on the diffuser when they went to bed and the diffuser released the scent for two hours at night when they were sleeping. The control group received bottles of distilled water with a minimal amount of deodorant to use in the diffuser.

All subjects were assessed at the beginning of the study and at the end of the study (after six months). The assessment contained olfactory abilities (smelling sticks were used), cognitive abilities (assessment of verbal learning and memory, working memory and planning and attention switching tasks) and mental health status. All participants also had brain imaging completed (fMRI scans).

The results were quite impressive because they showed an improvement in both cognitive and neuronal functions. The participants in the olfactory enrichment group had a 226% improvement in learning and memory. The FMRI studies results showed improvement in the left uncinated fasciculus, which is a part of the brain that is involved in episodic memory, memory retrieval, language, and socio-emotional processing.

However, the above study was done on a relatively small group of subjects. Intrigued by the idea, I dove deeper into the subject and found more research on humans and animals which indicated that smell training may improve memory and also other cognitive functions.

In a 2022 study (Cha, H. et al.), 34 patients with dementia in the experimental group were exposed to intensive olfactory training for 15 days (twice a day, a 40-odor set). The control group contained 31 individuals receiving “conservative management”. The results indicated that intensive smell training improved memory, attention language function, and also depression in participants. In an animal study, (Veyrac, A. et al. 2008) the results indicated that when mice were repeatedly daily exposed to a single novel odorant they showed improvement in short-term olfactory memory and neurogenesis in the mouse olfactory bulb.

In a 2022 study (Oleszkiewicz, A. et al.), 55 participants (mean age 58.2) with impaired olfaction were randomly assigned to the standard, twice-daily olfactory training or intense, four-times-a-day training. The participants were given an electrical odor dispenser and were instructed to sniff each five odors for 30 seconds. The results indicated that participants in the twice-a-day olfactory training group showed improvement in verbal semantic fluency and olfactory functions. Some studies indicated that olfactory training can improve verbal functions and subjective well-being in older adults (Wegener, B.A. et al. 2018) and executive functions in patients with mild cognitive impairment (Haehner, A., et al. 2022).

The studies above concluded that olfactory training could be an effective method for preserving and enhancing memory and other cognitive functions in the elderly. This method is also feasible (two hours at night) and has a low cost (requires an infuser and some essential oils), compared to some expensive medications used to prevent cognitive decline in older adults. It's important to note that the loss of smell is often the first indication of future cognitive decline. Therefore, it's crucial to pay attention to our olfactory functions, especially considering that, reportedly, about 70 neurological and psychiatric disorders are linked to some degree of olfactory loss.