Smelly Facts: Sense of Smell & Pregnancy

A few years ago, in 2007, I had reported here on Fragrance Bouquet on the mistaken, yet still propagated belief that the adult brain does not produce new neurons. In that post I explained that one of the two identified areas in the brain that constantly see the birth of new neurons is the olfactory system (the other is the hippocampus). As I reported back then, neurons in the olfactory system constantly die off, mostly due to their constant exposure to harmful agents and thankfully, they are constantly replaced. Recently, while reading the astonishingly interesting and very humorously written “Why Zebras don’t Get Ulcers” by Robert M. Sapolsky as part of the obligatory books to be learned for my exams in Health Psychology, I came across the following related excerpt which I provide here for your pleasure:

“It turns out that there is a huge burst in the production of those new olfactory neurons early during pregnancy. They are fully on line just around the time of birth, and the scientists who discovered this speculated that these new olfactory neurons are tagged for the task of imprinting forever on the smell of your offspring (a critical event for mothers of most mammals). And what happens early in pregnancy, when those new olfactory neurons are showing up, but not quite making sense yet? I bet this has something to do with the famed nausea of pregnancy, the food aversions and olfactory sensitivities.”

- Sapolsky, R. M., 2004. Why Zebras don’t Get Ulcers. New York, NY: Henry Holt and Company, LLC

Image: Flickr by Raphael Goetter

Smelly Facts : Neuron Renewal

Have you ever heard others say that the adult brain has a fixed number of neurons and is unable to generate new ones once these die out? Indeed it was traditionally believed among scientists that the adult vertebrate brain could only lose neurons, never gain. (Kalat, 2007) Recently though, a small number of exceptions have been found. Among them, and of special interest to us of course, are the olfactory receptors. Indeed, these only tend to survive a couple of months at best, due to the fact that they constantly come into contact with harmful chemicals, as well being subjected to natural wear and tear, exposed as they are to the natural world. Thankfully, the dying olfactory receptors are constantly replaced by new developing cells! Too, adult stem cells within the brain have the ability to propagate daughter cells. These “migrate to the olfactory bulb and transform into glia cells or neurons" (Gage, 2000).


References: Graziadei & de Han, 1973, Gogos et al., 2000 and Kalat, 2007.

Image: Coronal section of olfactory bulb, http://commons.wikimedia.org