I was doing a little baking this week for a church bake sale. The house will filled with the smell of cinnamon combined with other spices and this got me to thinking about the holidays. It is said that our sense of smell is mostly linked to memory, so what smells make you think about Christmas?
Despite the tendency of humans to underestimate the role of smell in our every day lives, for most mammals, smell is the most important sense. Dogs are probably the most obvious example of this, it is through the use of the olfactory system that animals are able to find food, reproduce, and even communicate. While being one of the oldest and important parts of the brain, our failure to fully realize the importance of the olfactory system resulted in it being surrounded by numerous questions. How does it work? How do we identify smells? While these are only a few questions out of a whole list, research has progressed in recent years that we know much more about the olfactory system than before, but the fact remains that much remains to be found.
An important quality of the olfactory system is that information travels both to the limbic system and cortex. The limbic system is the primitive part of the brain that include areas that control emotions, memory and behavior. In comparison the cortex is the outer part of the brain that has to do with conscious thought. In addition to these two areas, information also travels to the taste sensory cortex to create the sense of flavor. Because olfactory information goes to both the primitive and complex part of the brain it effects our actions in more ways than we think.
Many wonder how certain smells able to trigger memories of events taking place several years ago despite the fact that sensory neurons in the epithelium survive for about only 60 days. The answer is that the neurons in the epithelium actually have successors. As the olfactory neurons die, new olfactory neurons generated by the layer of stem cells beneath them, which eventually takes the role of the old neuron as it dies. Linda Buck points out that the key point to the answer is that "memories survive because the axons of neurons that express the same receptor always go to the same place". The memories are stored in the hippocampus, and through relational memory certain smells trigger memories.
So, what smell triggers your Christmas memories? Is it the smell of the fresh evergreen decorated in your home? Or the odour of baking permeating the house in the month of December? Or that scent of chocolate and melted marshmallow as you just get in from an afternoon of sledding with the kids? Or the smell of the turkey cooking in the oven as you visit your parent's home during the holidays?
Whatever smells help you remember Christmas, each one is a cherished memory that your brain will keep filed away until that particular blend of chemicals enter your olfactory center once again.