Overnight Olfactory Enrichment Improves Memory

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You may have enjoyed the pleasant scents from an essential oil diffuser before, or perhaps you own one in your home. While most people buy these for the intent of making their space smell nice, new research suggests that there may be a hidden perk that these odorant diffusers can provide. A recent study published in July of 2023 by the Department of Neurobiology and Behavior at the University of California, Irvine showed that adults who experienced olfactory enrichment overnight via an odorant diffuser and various essential oils showed a 226% improvement in memory and cognitive function.

“…one in ten adults aged 65 or older have dementia, and 22% are faced with mild cognitive impairment.”

Dementia and cognitive impairment are on the rise with research finding that one in ten adults aged 65 or older have dementia, and 22% are faced with mild cognitive impairment. While these rising rates are often blamed on an aging population, a more plausible explanation is that they are the results of our unhealthy lifestyle which make the brain more susceptible to degenerative changes in older age. Currently, there are no effective and cost-efficient ways for treating cognitive impairments in older adults. Some evidence supports the effectiveness of flavanol supplements in some individuals, and the consumption of a largely plant based diet, like the MIND diet. However, there is a clear need for new approaches to be discovered that will help to treat the increasing number of older patients experiencing memory loss and a decrease in their cognitive function.

In laboratory mice, olfactory enrichment has been shown to improve cognition in a similar way as it does for aging human adults. Olfactory enrichment in the laboratory is achieved by routinely exposing individuals to various odorants and in mice. This intervention was found to be successful in not only improving memory, but symptomatic improvement was associated with neurogenesis (the process in which new neurons are formed in the brain) and memory.

The olfactory system is responsible for our sense of smell, and has a direct connection to the emotional brain networks which play a crucial role in memory and emotion. This system includes hippocampus a brain region involved in the encoding and retrieval of memory which is negatively affected by the onset of dementia. The close connectivity between olfaction and brain networks involved in memory and emotion suggests that scents may have a special role in preserving or improving memory by directly activating these brain networks.

Smells have the power to potentially evoke hidden memories and can even take us back to a time in our past. However, the scientific literature shows that the loss of smell can be predictive of the development of neurological diseases, including types of dementia such as Alzheimer’s Disease. Furthermore, scientists are also seeing that both the olfactory sense and cognitive function will start to significantly decline in most adults over the age of 60. Unlike being prescribed eyeglasses for having poor eyesight, there is currently no treatment available for losing one’s sense of smell. In view of the close connection between cognitive function and the sense of smell, it is imperative that we seek a possible solution to prevent memory loss by stimulating the olfactory system.

In a 2022 study, Cha et, al. found that adults who were diagnosed with moderate dementia were showing significant improvements in their memory, emotions, language, verbal skills, and sense of smell after being exposed to a total of 40 various odorants twice a day over the course of 15 days. While this research was indicative of the powerful connection between sense of smell and memory, it is not probable that an older adult with dementia would be smelling 40 different scents twice a day. However, these findings did suggest that stimulating the olfactory system could be an effective way to increase memory and promote neurogenesis in adults.

“They intended to evaluate the potential effectiveness that the use of overnight olfactory enrichment would have on healthy older adults in improving their cognitive function.”

The researchers at UC Irvine enrolled 43 male and female participants aged 60-85 to participate in their study. To test the hypothesis that the use of overnight olfactory enrichment in healthy older adults is able to improve cognitive function, participants were randomly assigned to the Olfactory Enriched or a Control group. The Olfactory Enriched group was exposed to seven different odorants each week with one aroma per night for the duration of two hours via an odorant diffuser. The Control group underwent a similar protocol, but the enrichment occurred with aromas of minimal strength. The process of using the odorant diffuser overnight lasted for the course of six months.

The overnight approach takes away the added responsibility of individuals having to be reminded to take the time to smell the odors throughout their day. It would be difficult for an individual to realistically set the time aside to smell multiple scents a day, let alone an individual experiencing memory loss. The use of an odorant diffuser overnight makes this task a much more realistic and attainable solution, provided the individuals are still able to receive the same benefits while smelling the aromas when sleeping throughout the night.

“They found a statistically significant improvement of 226%… suggesting that the use of overnight olfactory enrichment may be an effective and efficient treatment option for improving cognitive function and memory.”

After six months of each group experiencing the various scents via the odorant diffuser, the researchers tested the cognitive ability of each group. They used the Rey Auditory Verbal Learning Test to evaluate cognition along with fMRI scans to detect changes in hypothesized brain regions. Brain imaging results obtained at baseline, before beginning the intervention to the follow up were compared with images obtained after the course of six months. They found a statistically significant improvement of 226% in the Olfactory Enriched group compared to the Control group, suggesting that the use of overnight olfactory enrichment may be an effective and efficient treatment option for improving cognitive function and memory.

While there has been a long-understood connection between memory and smell, these recent findings reported from the research at UC Irvine, provide evidence for a realistic, efficient, and cost-effective treatment solution for older adults who are suffering from memory loss or cognitive decline. Even though the overnight use of odorant diffusers and essential oils is a is a promising approach to boost memory and potentially prevent the onset of dementia in older adults, confirmative evidence from larger studies is needed before this strategy can be recommended as a treatment for cognitive decline.

Amanda Johnson Amanda is a recent graduate from the University of Southern California where she received her degree in Psychology. In addition to her university studies, she earned her Integrative Nutrition Health Coach certification from the Institute of Integrative Nutrition (IIN).

This article was reviewed and approved by Emeran Mayer, MD