חמרא וריחני פקחין

Pointing to scientific discoveries and saying "See, just like it says in Chazal!" is risky. But here's an interesting development. 

Horyos 13b

חמשה דברים משיבים את הלימוד פת פחמין וכל שכן פחמין עצמן והאוכל ביצה מגולגלת בלא מלח והרגיל בשמן זית והרגיל ביין ובשמים והשותה מים של שיורי עיסה ויש אומרים אף הטובל אצבעו במלח ואוכל הרגיל בשמן זית מסייע ליה לרבי יוחנן דאמר רבי יוחנן כשם שהזית משכח לימוד של שבעים שנה כך שמן זית משיב לימוד של שבעים שנה: והרגיל ביין ובשמים:  מסייע ליה לרבא דאמר רבא חמרא וריחני פקחין:

The Gemara recommends five things for retention of knowledge. Of the five, two are stated in the singular, as one one-time actions, which indicates to me that they function as segulos, and three are recommended for regular use, which implies, to me, that their efficacy is biology based, not magical. The three are שמן זית יין ובשמים.

Olive oil, wine, and fragrance. Rava offered his positive personal experience in regard to two - Rava said that wine and fragrance enhanced his wisdom. (I have written elsewhere about a possible homiletic interpretation of Rava's words. I have also written about olive oil.)  Just today, I came across an amazing article that relates to fragrance.

Overnight olfactory enrichment using an odorant diffuser improves memory and modifies the uncinate fasciculus in older adults

Here is the introduction.

Objective: Cognitive loss in older adults is a growing issue in our society, and there is a need to develop inexpensive, simple, effective in-home treatments. This study was conducted to explore the use of olfactory enrichment at night to improve cognitive ability in healthy older adults.

Methods: Male and female older adults (N = 43), age 60–85, were enrolled in the study and randomly assigned to an Olfactory Enriched or Control group. Individuals in the enriched group were exposed to 7 different odorants a week, one per night, for 2 h, using an odorant diffuser. Individuals in the control group had the same experience with de minimis amounts of odorant. Neuropsychological assessments and fMRI scans were administered at the beginning of the study and after 6 months.

Results: A statistically significant 226% improvement was observed in the enriched group compared to the control group on the Rey Auditory Verbal Learning Test and improved functioning was observed in the left uncinate fasciculus, as assessed by mean diffusivity.

Conclusion: Minimal olfactory enrichment administered at night produces improvements in both cognitive and neural functioning. Thus, olfactory enrichment may provide an effective and low-effort pathway to improved brain health.

Along the way, the article cites research showing that cognitive decline goes hand in hand with olfactory decline; that increased exposure to olfactory stimulation restores olfactory sensitivity; and that two hours, while sleeping, of exposure to fragrance produced by a diffuser, led to fantastic cognitive improvements. The improvement was also seen in MRI scans of the  the uncinate fasciculus, the part of the brain related to learning and memory, which deteriorates in patients suffering from dementia.

Those of you who think that ריחני of Rava's חמרא וריחני were cannabis, here's a better pshat. And even if you look askance on the מי שאחזו pharmacopeia, you might want to go out and invest in a diffuser or a nebulizer for your bedroom. Here are some ratings. The last one in the list uses pure essential oil, not oil mixed with water.

Enquiring minds want to know: 

1. I don't know why they used it during sleep. It should be equally efficacious while you're awake. But I just do not know the mechanism involved.

2. Does this work only with pleasant smells, or anything that stimulates the olfactory sense, even noxious odors? 

3. I think, I imagine, that this only works when the fragrance is not constant. A constant stimulus eventually is not even sensed. If it did, then plumbers and sanitation engineers and people who wear cologne or perfume would be immune to dementia, and that's obviously not the case.