It’s that time again, the holidays. For me, like many, it’s a time for nostalgia; mulling spices in the kettle on the wood stove in Maine, filling the house I grew up in with aromas of cinnamon and clove… decorating our freshly cut pine tree with peppermint candy canes… and my Grandmother’s kitchen filling with the smell of melting sugar and butter as she made her famous chocolate fudge.
Photo from Flickr courtesy of vanlaar
It is no coincidence that these aromas are so strongly linked with vivid memories of the holidays as a kid. When we smell something tied to an emotional experience, like the comforts of family around the holidays or the excitement of reindeer on rooftops, the neurons that hold that well preserved memory are directly linked to the sensory neurons that hold the related smells that were there when that memory was formed. This linking leads to these neurons firing together when we smell that familiar aroma again, and the result is that we remember. For me, last night making fudge here in Denver with my sister, I was transported back to my late Grandmother’s kitchen, stirring the bubbling sugar and butter as she taught me her secret recipe. It’s a powerful thing that ability of smell, and above all other senses, it can bring us back to a time long passed.
In that spirit I asked my friend and colleague, Dr. Ernesto Salcedo, our resident olfaction expert, to break down the science behind this phenomenon of smell.
Enjoy this bit of holiday science, and from everyone in the Genetics of Taste community research lab, we wish you happy holidays, and a healthy and happy new year!
Yo Pearl the Science Girl (aka Nicole Garneau)
It turns out that the act of smelling is in fact deceptively simple. With a single sniff, the average human is capable of discriminating between roughly millions of different odors right from birth. One of the reasons we are able to do this is because we have nearly 500 genes (genes are like recipes for your body) devoted to helping your body make the actual proteins in your nose that detect odor molecules. There are only about 25,000-30,000 proposed genes in the human genome, so nearly 1 in every 50 genes are devoted to our sense of smell!
These proteins, called odorant receptors, act like tiny little molecular locks which can only be opened by specific odor molecules. Each smell gene makes a slightly different lock that can be opened by a slightly different set of odor molecules. These little locks are found in the cells in the very back of our noses called olfactory sensory neurons. The opening of one of these locks by an odor molecule causes the cell to send an electrical signal down a very thin strand of fiber (called the cell’s axon) that is directly connected to the brain. Some of these signals go to the part of the brain that works to identify the odor. Other signals are sent directly to our emotional and memory centers, which is why some smells have a strong memory associated with them, and which is why the aromas of the holidays can be so comforting as memories of family and good eating can come flooding back.
Of course, retailers have figured out how to take advantage of this smell-emotion relationship. Studies have shown that the smell of cinnamon has the potential side effect of over-exuberant shopping sprees, which is why stores often laden their stores with the smell of cinnamon during the holiday shopping season!
Thanks to Ernie for this guest blog post!
For more great information on the olfactory system, you can check out the Nobel Prize website. The Prize in Physiology/Medicine in 2004 was awarded jointly to Richard Axel and Linda B. Buck "for their discoveries of odorant receptors and the organization of the olfactory system."