Olfactory Therapy Sounds Like Aromatherapy

Not sure I can believe all this - because you know as they say, extraordinary claims require extraordinary evidence. 

We're talking about a thing called therapeutic olfactory stimulation, also called olfactory enrichment and olfactory therapy. We start with the first study, which says: 

"Olfactory enrichment can improve the memory of older adults by 226%" 

They took 43 people over 60 years old and exposed them to 7 different odorants a week, one per night, for 2 hours, using an odorant diffuser, and then gave them the Rey Auditory Verbal Learning Test where they saw improved scores, and gave them fMRI scans that showed improved functioning in the left uncinate fasciculus as assessed by mean diffusivity.

I'm not a research scientist working in a lab and writing papers, and so the only thing I see here that's a flag is that the study took place during the covid lockdown, and something about social interaction related to the study could definitely improve brain health, because we know that happens. But that also caused lots of other problems like how they had to remove people from the study because their baseline taken in the office might be so different from follow-ups done remotely. 

They do reference a few other studies that support this idea, so I'll just copy directly:  

...olfactory stimulation during sleep deepens slow-wave sleep (Wolfe and Herzberg, 1996; Goel et al., 2005), which is the most restful portion of the sleep cycle, and people report feeling more vigorous the next day after nighttime olfactory exposure (Goel et al., 2005). Odorants enhance normal sleep, and they also improve abnormal sleep at a magnitude similar to that of sleep medication (Hardy and Kirk-Smith, 1995).

Bottom line is, I think we are eagerly awaiting another study, done not-during a pandemic and with a larger group beyond the 43 people participating here. 

via University of California Irvine Center for the Neurobiology of Learning and Memory: Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults. Cynthia C. Woo, Blake Miranda, Mithra Sathishkumar, Farideh Dehkordi-Vakil, Michael A. Yassa, Michael Leon. Frontiers in Neuroscience, 2023; 17 DOI: 10.3389/fnins.2023.1200448 [full text available]

https://doi.org/10.3389/fnins.2023.1200448

Image credit: AI Art - THC Oil Cartridge w Good Image - 2024

But not so fast, we're not done yet. If the results from the above study are found to be credible, that would make the study below a lot more important:

Smell loss is linked to more than 100 diseases in new study

Oct 2024, phys.org

https://medicalxpress.com/news/2024-10-loss-linked-diseases.html

"We now know that pleasant scents can decrease inflammation, potentially pointing to the mechanism by which such scents can improve brain health." The study delves into the methodical tracking of 139 medical conditions associated with both olfactory loss and heightened inflammation, uncovering insights into a shared pathway linking these factors. Olfactory loss, which often precedes conditions such as Alzheimer's and Parkinson's diseases, may serve as an early indicator of disease onset, allowing for more proactive therapeutic approaches.

By showing how olfactory enrichment can mitigate inflammation, this research has laid a foundation for future studies aiming to explore the therapeutic use of scent to address a broader range of medical conditions.

via Charlie Dunlop School of Biological Sciences at University of California Irvine and Oxford Research Centre in the Humanities: Michael Leon et al, Inflammation and olfactory loss are associated with at least 139 medical conditions, Frontiers in Molecular Neuroscience (2024). DOI: 10.3389/fnmol.2024.1455418

https://dx.doi.org/10.3389/fnmol.2024.1455418

Olfaction and Mental Health

Image: Ship of Fools, a reference to Michel Foucault's Madness and Civilization

The following article/abstract is quoted here as an introduction to the practice of using olfaction to better understand mental health:

The human brain representation of odor identification

Grete Kjelvik , Hallvard R. Evensmoen , Veronika Brezova , Asta K. Håberg, Journal of Neurophysiology. Published 15 July 2012. Vol. 108, No. 2, 645-657 DOI: 10.1152/jn.01036.2010

Odor identification (OI) tests are increasingly used clinically as biomarkers for Alzheimer's disease and schizophrenia.

ODOR IDENTIFICATION (OI) tests examine an individual's ability to correctly name an odor. In the clinic OI tests have been shown to have high sensitivity and specificity for predicting Alzheimer's disease (AD) at an early stage. This OI deficit is considered a central phenomenon as olfactory threshold, detection, and discrimination abilities are preserved (Arnold et al. 1998; Morgan et al. 1995; Serby et al. 1991; Wilson et al. 2007, 2009). Since AD pathology is first observed in entorhinal cortex and subsequently in the hippocampus (Braak and Braak 1992), OI impairments may arise from medial temporal lobe (MTL) pathology. Indeed, the early and specific OI deficit in AD correlates with the number of tangles in entorhinal cortex and the hippocampus (Wilson et al. 2007), and left hippocampal atrophy (Murphy et al. 2003). Structural changes in the entorhinal cortex and hippocampus are also present in patients with schizophrenia (Baiano et al. 2008; Bogerts et al. 1985; Ebdrup et al. 2010; Schultz et al. 2009; Witthaus et al. 2009), another group of patients with a specific OI deficit (Atanasova et al. 2008; Moberg et al. 1997, 2006; Rupp 2010). The utility of OI tests as a clinical tool depends on a better understanding of the neuronal processes underlying OI, and how OI differs from passive smelling (PS).

Notes:

This point about smelling mental illness is fantastically queried by the odor author Annick Le Guérer in Scent the Mysterious and Essential Powers of Smell (1992), where she plays with the possibility of the “odor of sanctum” reported to emanate from certain saintly corpses as a result of extensive abnormal mental states which lower, or encumber the metabolic rate, leading to incomplete combustion of aromatic materials in the body. She reciprocates by suggesting such lower metabolism as a result of sustained meditation. Regardless, it is a general understanding that psychosis brings with it an identifiable smell.