Have you ever taken a deep breath and pulled in a smell that brought back a passed relative? Or smelled a hoodie of someone you loved and just knew it belonged them? My dad still smells his dad throughout our house on old shirts. Smell is very powerful. My favorite smell is the smell of my grandparents’ house. Every time I enter that house and smell the memories in that house, it changes my whole day.

The olfactory nerve, the nerve that brings smell from your nose to your brain, runs along the same path within your brain as your memories. Therefore, it is very easy for smells to provoke memories. Psychology Today and Penn State’s Dr. Lewis explains how the olfactory bulb is directly associated to both the hippocampus and the amygdala. Both of these are strongly tied to emotion and memory. There is nothing better than running into a great old scent that brings back days worth of great memories. What is not so great is when smells bring back negative memories and emotions for people such as those with PTSD.

Another negative effect of this connection is a new study being done including smell and pain. In online Science Advances, it was seen that mice that slept in the same bedding as those mice that were in pain tended to be more sensitive to pain themselves. Neurologist Andrey Ryabinin had a goal to study through mice, whether pain could be sensed through that same olfactory bulb.  The mice within this study specifically were mice suffering from alcohol withdrawal. These mice in pain had developed a very low pain tolerance and were very sensitive to the touch of an extremely thin fiber. It was very evident within its cagemates that the same mice that were completely comfortable and healthy up until this point became equally as sensitive to the touch of the fiber. Ryabinin and colleagues tested these mice otherwise through several other tests. These showed quick reactions such as pulling thier tails out of hot water and licking thier paws after been given shots.

Neuroscientist Christian Keysers does a good job at looking at third variables. He states how he believes the data is strong enough to prove that scent can transmit pain, however he also looks at the other senses of the animal noting that sight and sound could very well be the causal variable. While the scent could be bringing the sensitivity, its very possible that the other senses could be working as the causal variable and creating the dependent variable, the sensitivity.

The overall claim however of the study is that the causal variable, scent, is creating a sensitivity to pain that only animals are able to sense. Because humans lack the olfactory skill that animals do, we are unable to experience this for ourselves in order to clarify this study. The dependent variable is seen as the sensitivity or lowered pain tolerance. Its possible that reverse causation could be at work here. In order for reverse causation to be influencing this study, we would have to be able to say that the sensitivity is causing the smell. This is very possible. If the mice feel overly sensitive to pain, this may cause them to feel weaker and to almost wear away. Referring to anything that usually rots or wears, a bad smell may or may not be a part of the outcome. Although this is unlikely, it is a possibility.

As stated above, Keysers does look into possible third variables. There are several different variables that need to be taken into consideration. The simple fact that the mice under test are suffering from alcohol withdrawal is a huge part of the experiment that makes us question the existence of  third variables. Mice that have been under the influence of alcohol, could have aquired some mental difficulties that cause them to be ultra-sensitive to touch or pain and could rule out the scent’s influence. Additionally, we need to look at the type of mouse. Studying with a single breed of mouse makes it hard for scientists to know whether or not the reaction truely was based off the smell or if that specific breed of mouse tends to be sensitive in general.

Another difficulty I see with this study is how they measure the pain of the mice. When they tested the mice by dipping their tails and giving them shots, could the reactions simply be the third variable of a natural reaction? This is something that needs to be addressed. It seems as if correlation does not equal causation when it comes to these mice.

https://www.sciencenews.org/article/mice-smell-share-each-others-pain

https://www.psychologytoday.com/blog/brain-babble/201501/smells-ring-bells-how-smell-triggers-memories-and-emotions