Sniffing Out Memories Keeps the Brain Fresh

Ever wonder how a fragrance can unlock a once-forgotten memory?

In a study published in Frontiers in Neuroscience, UC Irvine scientists have discovered that exposing older adults to complex smells while they slept, improved their cognitive and neural functioning. 

The ability of smell to transport you to a time and place of the past can be a beautiful driver of nostalgia.

But could the scent of madeleines do more than just prompt a smile?

Interestingly, there is a direct connection between our olfactory system and the brain regions crucial for memory and emotion. Taking advantage of this Proustian pathway, scientists have questioned whether overnight odorant diffusion can strengthen memory and brain connections in older adults.¹

Passing the Smell Test

As we age, our sense of smell is the first sense that starts to decline. Previous research linked loss of smell with memory impairment, and the association between odorant use and improved memory.^2,3

This intriguing observation has been difficult to put into practice because the experiments required the test subjects to sniff up to 80 different scents—that’s a lengthy daily routine. This study, however, took a novel approach. The researchers measured the effect of odorant diffusion at night.¹

Since overnight aromatherapy is as simple to try as adding a few drops of oil to a diffuser before hopping into bed this made for an easy fix.

The study enrolled participants who met the following essential criteria:

• Male or female aged between 60 and 85.
• Good health.
• The ability to smell odours.
• Fluent in English.
• Willing to avoid scented oils and candles for the duration of the study.

The study randomly assigned 20 participants to nightly essential oil exposure. The remaining 23 participants served as a control and experienced low levels of odorant each night.

The researchers assessed the participant’s cognition before and after the six-month intervention. They did this using several memory tests. Similarly, the participants had an MRI before and after the study to track any changes in the brain.

Improvements in Cognitive Scores

Regarding learning and memory, the overnight odorant group experienced a 226% improvement compared to the untreated control group.

The MRI findings were also promising. Scans taken after the trial showed improved brain function in the exposed participants compared to the control group. Odorant use also targeted brain regions linked to language, memory, and emotional processing.

As these regions decline during Alzheimer’s disease, these findings offer a practical prevention measure.

Unfortunately, the Covid-19 pandemic impacted data collection. Social distancing meant the follow-up memory test could not occur in person. Instead, the study included participants who completed their six-month intervention before the pandemic.

They excluded those who completed the tests at home. The researchers cited the reduced sample size as a limitation of the study. 

Silver Linings

However, the pandemic did not serve as a complete disadvantage. As a link exists between COVID-19 infection and loss of smell, the researchers adapted the study to include this factor.

They wanted to determine whether exposure was associated with any brain changes. If changes did exist, they also wanted to assess if odorant diffusion improved it.

For the MRI assessment, the study further divided groups into whether they had a history of infection or not.

The results revealed that COVID-19 infection did not affect brain function in the control or odorant-exposed group. More research is needed since this finding contrasts with previous research on the impact of Covid-19 on brain health.

Encouraging Results

Although in its infancy, many believe the field of sensory stimulation holds real potential.

Following the success of music therapy for dementia patients, the next logical step was to test its potential for olfaction.⁴ The current study proposes that overnight odorant use may offer a low-cost, practical approach to improving memory.

However, an unmet need remains to verify its value in younger adults and those with an existing cognitive impairment.

References

1. Woo, C.C. et al. Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults, Frontiers in Neuroscience 2023; 17. doi.org/10.3389/fnins.2023.1200448

2. Doty, R.L. et al. Smell identification ability: Changes with age, Science, 1984; 226 (4681), pp. 1441–1443. doi:10.1126/science.6505700. 

3. Birte-Antina, W. et al. Olfactory training with older people. International Journal of Geriatric Psychiatry, 2017; 33(1), pp. 212–220. doi:10.1002/gps.4725. 

4. Sihvonen, A.J., Soinila, S. and Särkämö, T. Post-stroke enriched auditory environment induces structural connectome plasticity: Secondary analysis from a randomized controlled trial, Brain Imaging and Behavior 2022; 16(4), pp. 1813–1822.