More evidence of the positive effects of training on specific anosmia…

In yet another paper concerning training for specific anosmia (=inability to smell a specific odor), it appears that training with the specific odor can overcome the anosmia.*

Although we have some 400 functional odor receptor genes, it seems that we only express somewhere around a fourth of the possible receptors in our nose at any one time. Croy and her colleagues calculated that it is likely that each one of us has an anosmia to at least one specific compound, simply because we do not express all possible receptors. 

We do not know why we don’t express all possible receptors at any one time. There is redundancy in the olfactory system: most odors activate more than one type of receptor. So you may in fact not need expression of all genetically possible receptors. Furthermore, it may be helpful to limit the number of functional receptors expressed in the nose in order to help the signal from important odors in the environment stand out: if you only express receptors for those odors that are important in your environment, your detection capacities won’t be swamped by signals from all the other possible odorants in your environment. 

This is where training comes in: frequent exposure to an odorant over a couple of months would appear to make it salient in your environment.  Croy and her colleagues found that all 25 of their study participants who underwent training no longer had the specific anosmia that they had manifested before training, as shown in the following figure:

What exactly happens with training is unknown:

• One possibility, as suggested above, is that you start to express receptors for the odors with which you trained. 
• Another possibility (which doesn’t exclude the first) is that your entire smell system, from nose to brain, rearranges itself to become more sensitive to signals from the trained odorant.
• A third possibility is that the trigeminal system in your nose becomes more effective at increasing the gain from a faint subthreshold signal so that it is now actively perceived.

It’s my guess that all of these mechanisms come into play. As Croy and her colleagues conclude:

“We propose specific anosmia to occur as a rule, rather than an exception, in the sense of smell. The lack of perception of certain odors may constitute a flexible peripheral filter mechanism, which can be altered by exposure.”

My conclusion: it is worthwhile to contemplate a training course for tea aromas as well as wine, to enhance your capacity to appreciate the many flavor facets of your favorite beverage. 

Keep your eyes on this blog, because friend of Pairteas Marzi Pecen is hard at work creating such a training system, and I'll let you know when it's ready.

* Ilona Croy, Selda Olgun, Laura Mueller, Anna Schmidt, Marcus Muench, Cornelia Hummel, Guenter Gisselmann, Hanns Hatt, Thomas Hummel. Peripheral adaptive filtering in human olfaction? Three studies on prevalence and effects of olfactory training in specific anosmia in more than 1600 participants. Cortex, Volume 73, December 2015, Pages 180–187. doi:10.1016/j.cortex.2015.08.018.