Memory significantly improved with nighttime olfactory enrichment

A study from the University of California reports a 226 percent statistically significant improvement in verbal learning and memory in older adults with normal cognition using nighttime olfactory enrichment.

“Cognitive loss in older adults is a growing issue in our society, and there is a need to develop inexpensive, simple, and effective treatments that can be used at home,” wrote the researchers. Olfactory enrichment was chosen on the basis of prior research indicating that it improves cognition in humans, including in older adults with normal cognition, as well as Parkinson’s disease and dementia patients. [Eur Arch Otorhinolaryngol 2022;279:225-232; Int J Geriatr Psychiatry 2018;33:212-220; PLoS One 2013;8:e61680; Geriatr Gerontol Int 2022;22:5-11]

Study participants were 43 community-dwelling older adults (age range, 60–85 years) with no diagnosis of cognitive impairment or dementia, who were randomly assigned to 2 hours of nighttime exposure to essential oil scents delivered via a diffuser (n=20) or to a sham control condition with trace amounts of odorant (n=23). The enriched group received seven essential oils (rose, orange, eucalyptus, lemon, peppermint, rosemary, and lavender), which were rotated every night. [Front Neurosci 2023;doi:10.3389/fnins.2023.1200448]

“Since high levels of compliance are important to ensure maximal benefit from olfactory enrichment, we tested whether enhanced neural and cognitive outcomes could be achieved with minimal-effort olfactory enrichment at night,” explained the researchers.

Neuropsychological assessment after 6 months of intervention showed a clear, statistically significant (p=0.02) 226 percent difference between the enriched and control group in the Rey Auditory Verbal Learning Test, which evaluates verbal learning and memory, including proactive interference, retroactive interference, delayed recall, retention, and recognition memory.

In addition, the researchers found that the mean diffusivity in the uncinate fasciculus increased in response to olfactory enrichment. “The uncinate fasciculus is a major pathway that connects the basolateral amygdala and the entorhinal cortex to the prefrontal cortex, which has been implicated in episodic memory, language, socio-emotional processing, and selecting among competing memories during retrieval. This pathway has been shown to deteriorate with age and in patients with Alzheimer’s disease,” they highlighted. [Brain 2013;136:1692-1707; Aging Ment Health 2019;23:831-839; Neuroimage 2016;132:213-224]

“We have shown that even minimal olfactory enrichment, delivered at night, is sufficient to induce an improvement in cognition and neural function. This type of sensory enrichment may be particularly useful, as it is low-cost, as well as low-effort,” concluded the researchers.