You catch a whiff of freshly-baked banana bread, and suddenly you are on the porch of your grandmother’s summer house, looking for dragonflies in the evening heat. Or perhaps a vendor full of mint-chocolate goodness throws you back into the anxiety of your finals when you try to chew your troubles away.

In any case, what you experience is a neuroscience phenomenon known as the Proust effect – named after an author who wrote a book inspired by just one aroma of madeleines. What makes these evoked memories so vivid is the closeness of the smelling, “olfactory” processing system to the memory and emotion centers of the brain.

Out of the five senses – sight, sound, smell, touch, and taste – every sense except for smell has to pass through the thalamus to be processed by the brain. Thalamus is a sort of railway station in the brain, a hub through which all the information has to pass on the way to its destination. But the smell bypasses the thalamus entirely and reaches the hippocampus (key role in long-term memory) and amygdala (which regulates emotions and encodes emotional memories) in a matter of a few synapses. Synapses are tiny gaps between the nerve cells, about 20 nanometers wide – that is, twenty billionths of a meter, so you can imagine how fast the smell moves to our memory and emotion centers.

Figure 1: (Curley), A. M. (n.d.). Making sense of scents: Smell and the brain. BrainFacts.org. Retrieved October 12, 2021, from https://www.brainfacts.org/thinking-sensing-and-behaving/smell/2015/making-sense-of-scents-smell-and-the-brain.

This is why your memories get triggered by smells so easily and why you get so sentimental over them. The smell bypassing the thalamus makes us lose the ability to process or even register the connections it forms with our emotional memory. How could we, if the signal blazes through our brain at over 100 mph a shorter distance than the width of a hair?

Why does it do that? Scientists are not sure, yet most agree that the cortex (the well-known “grey matter,” outer layer of the brain) evolved as an extension of the olfactory bulb. Just imagine, dogs have 2% of their brain dedicated to smelling – humans only 0.03%. Guess who has the hugest olfactory bulb compared to the rest of the brain? Turkey vulture!

The relationship between smell and memories is so deep that it also extends to health issues. Some studies show that a reduced sense of smell can be an early sign of diseases connected to memory loss, such as Alzheimer’s or Parkinson’s diseases.

We love smelling things. Sea salt, field flowers, french toast, engine oils (maybe not the latter.) So next time a smell sends you back the memory line, remember the little, easy-to-forget Proust effect, and be just a touch fascinated by that magnificent machine that is your brain.

References

  1. MediLexicon International. (n.d.). Why smells bring back such vivid memories. Medical News Today. Retrieved October 12, 2021, from https://www.medicalnewstoday.com/articles/322579.
  2. CogBlog – a cognitive psychology blog. CogBlog – A Cognitive Psychology Blog ” Smelling Your Memories? The Positive and Negative of the Proust Effect. (n.d.). Retrieved October 12, 2021, from https://web.colby.edu/cogblog/2015/11/22/smelling-your-memories-the-positive-and-negative-of-the-proust-effect/.
  3. Scientists in awe of huge olfactory bulb found in Turkey vulture brain. Smithsonian Insider. (2018, January 18). Retrieved October 12, 2021, from https://insider.si.edu/2017/12/scientists-in-awe-of-huge-olfactory-bulb-found-in-turkey-vulture-brain/.
  4. Featured image: Kanell, J., Kanell, A. J., & Author. (2020, July 28). Madeleines. Preppy Kitchen. Retrieved October 12, 2021, from https://preppykitchen.com/madeleines/.