The regions of the brain associated with olfaction are more developed in professional perfumers than in the general population. In addition, the quantity of grey matter in the experts' olfactory regions increases in proportion to their experience. [...] Based on anatomical MRI scans of professional perfumers, perfumery students and control subjects, it shows that training and practice make it possible to reverse the age-related grey matter reduction observed in olfactory regions among the general population.
— For the rest of us, these regions of the brain tend to shrink with age. Read more at Experience modifies the perfumer's brain at CNRS. They scanned the brains of perfumer Jean-Claude Ellena and students at the ISIPCA perfumery school, among others.
I cited this study on my blog not that long ago. The subject concerned how “objective” our sense of smell is. Another blogger claimed that the sense of smell is “unchanging” and implied that any “subjectivity” means a person has a kind of “broken nose.” I have found that certain notes “spike” during one wearing but not another, for example. I have experienced this several times. Then there is overall sensitivity, which seems to be subject to a great deal of variation as well. So, while we are all interested in learning about new “notes,” there seem to be other factors that many if not most never even consider!
It’s true, in fact I think there are so many factors that it’s hard to decide which are most important. But definitely not the case that our sense of smell is unchanging.