As our nation ages, individual and societal concern for brain health continues to skyrocket. Billions of research dollars go into finding the latest drug breakthrough or new therapy that might reverse dementia with its memory loss and cognitive processing issues. Others look at the preventive side hoping to avoid the decline in the first place as the reversal therapies so far have not been impressive. Meanwhile, there may be an effective option to improve memory at various stages of brain health that is right under our noses. In a study out of University of California, Irvine, researchers report that overnight exposure to 7 different essential oils produced a 226% improvement in a verbal learning test along with fMRI (functional MRI) measured functioning of a brain nuclei called the left uncinate fascilulus.
Various approaches to stimulating cognitive function has been attempted in lab animals for decades. Neuroplasticity is the term used to describe a brain’s ability to adapt and to improve responses to cognitive challenges. This neuroplasticity ability fades somewhat as animals, including humans age, but in some it fades much faster than in other. One of the approaches that has shown success in lab animals includes olfactory enrichment, or the regular exposure of the animal to various odorants (smells). Interestingly, in the mouse studies by Rusznak etal (2018), mixtures of such odorants did not improve mouse memory, but exposures to different odorants one at a time did improve memory and promote neurogenesis (new nerve cell growth) in not only the olfactory bulb but also the hippocampus. The hippocampus area of the brain is a major area for memory.
While exposing mice to various smells to stimulate their brains is only mildly exciting, the researchers knew from human studies that as humans’ ability to smell declined, their cognition seemed to decline as well. In studies by Doty et al.(1984) and Schaie et al. (2004) this olfactory decline occurred even before the cognitive decline was observed. Various other studies noted in the primary article link decline in olfactory function with the development of Alzheimer’s disease as well as Parkinson’s Disease, Lewy Body dementia, frontotemporal dementia, and other brain diseases. Interestingly, recent research has linked brain areas affected by olfactory loss to those affected by COVID infection. From there, other research noted in the article demonstrated that olfactory enrichment could improve function after olfactory loss due to post-infectious causes, head trauma, Parkinsons, and aging. Finally, prior studies showed that olfactory enrichment produced increases in some brain areas including the entorhinal cortex or hippocampus which are linked with memory function.
With all of this and other supporting studies in mind, the present authors wanted to know if nighttime exposure of humans to individual essential oils altered nightly could impact cognitive function. They randomly assigned 20 participants to receive nightly exposure to 7 different oil scents (rose, orange, eucalyptus, lemon, peppermint, rosemary, and lavender) and 23 to a sham control of only trace amounts of the oils. In preparation for the study, they measured a variety of cognitive functions using standardized tests and used a validated smell assessment called Sniffin’ Sticks (Sensonics) to measure any possible changes in olfactory ability. Both groups rotated different oils each night for 6 months in a diffuser from Diffuser World. The diffuser would run for 2 hours at the beginning of the night.
By the end of the six month study, they found a 226% improvement on the Rey Auditory Verbal Learning Test, which “evaluates verbal learning and memory, including proactive interference, retroactive interference, delayed recall, retention, and recognition memory.” They also found improved functioning in the left uncinate fasciculus, as assessed by fMRI. This brain pathway serves as a connector for the basolateral amygdala and the entorhinal cortex with the prefrontal cortex. (Ebeling and Von Cramon, 1992; Thiebaut de Schotten et al., 2012; Von der Heide et al., 2013) which declines in aging and Alzheimer’s dementia (Morikawa et al., 2010; Fan et al., 2019). Interestingly, improvements in olfactory ability did not improve statistically in this study.
Helping patients restoring healthier, more abundant lives includes a focus on brain function, especially as we age. With so many medications vying for our health care dollars, I am thankful that researchers like these are searching for simpler solutions which are available to more people earlier in their later years. With a little more digging, we look forward to implementing these safe and potentially effective therapies for our patients dealing with both mild cognitive decline (as well as more severe dementia), including the post-COVID effects we are seeing in so many.
Original Article:
Cynthia C. Woo, Blake Miranda, Mithra Sathishkumar, Farideh Dehkordi-Vakil, Michael A. Yassa, Michael Leon. Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults. Frontiers in Neuroscience, 2023; 17 DOI: 10.3389/fnins.2023.1200448
Thanks to Science Daily:
University of California – Irvine. “Sweet smell of success: Simple fragrance method produces major memory boost: Research into aromas while sleeping sparks 226% cognitive increase.” ScienceDaily. ScienceDaily, 1 August 2023. <www.sciencedaily.com/releases/2023/08/230801131700.htm>.
Further Bibliography:
Doty, R. L., Shaman, P., Applebaum, S. L., Giberson, R., Siksorski, L., and Rosenberg, L. (1984). Smell identification ability: changes with age. Science 226, 1441–1443. doi: 10.1126/science.6505700
Ebeling, U., and von Cramon, D. (1992). Topography of the uncinate fascicle and adjacent temporal fiber tracts. Acta Neurochir. 115, 143–148. doi: 10.1007/BF01406373
Fan, Y. T., Fang, Y. W., Chen, Y. P., Leshikar, E. D., Lin, C. P., Tzeng, O. J. L., et al. (2019). Aging, cognition, and the brain: effects of age-related variation in white matter integrity on neuropsychological function. Aging Ment. Health 23, 831–839. doi: 10.1080/13607863.2018.1455804
Morikawa, M., Kiuchi, K., Taoka, T., Nagauchi, K., Kichikawa, K., and Kishimoto, T. (2010). Uncinate fasciculus-correlated cognition in Alzheimer’s disease: a diffusion tensor imaging study by tractography. Psychogeriatrics 10, 15–20. doi: 10.1111/j.1479-8301.2010.00312.x
Rusznák, Z., Sengul, G., Paxinos, G., Kim, W. S., and Fu, Y. (2018). Odor enrichment increases hippocampal neuron numbers in mouse. Exp Neurobiol. 27, 94–102. doi: 10.5607/en.2018.27.2.94
Schaie, W. K., Willis, S. L., and Caskie, G. I. L. (2004). The Seattle longitudinal study: relationship between personality and cognition aging. Neuropsychol. Cog. 11, 304–324. doi: 10.1080/13825580490511134
Thiebaut de Schotten, M., Dell’Acqua, F., Valabregue, R., and Catani, M. (2012). Monkey to human comparative anatomy of the frontal lobe association tracts. Cortex 48, 82–96. doi: 10.1016/j.cortex.2011.10.001
Von Der Heide, R. J., Skipper, L. M., Klobusicky, E., and Olson, I. R. (2013). Dissecting the uncinate fasciculus: disorders, controversies and a hypothesis. Brain 136, 1692–1707. doi: 10.1093/brain/awt094
Sanctuary Functional Medicine, under the direction of Dr Eric Potter, IFMCP MD, provides functional medicine services to Nashville, Middle Tennessee and beyond. We frequently treat patients from Kentucky, Alabama, Mississippi, Georgia, Ohio, Indiana, and more... offering the hope of healthier more abundant lives to those with chronic illness.
