You may find that the smell of a gymnasium revives insanely vivid memories of your first ever gymnastics class, or the smell of coconut ice cream brings you to the lively beach boardwalk. But the same memories aren’t as vivid when you touch, see, hear, or taste something. Smell clearly seems to evoke memories, but what is the scientific explanation behind this? What difference in smell processing explains why memories aren’t as vivid in response to the 4 other senses?
Here is the reason. Whenever you taste, touch, see, or hear something, sensory information is sent to the thalamus, which then sends that information to corresponding and relevant parts of the brain which sometimes includes the amygdala, which handles emotional integration, and the hippocampus, which handles memory and cognition.
However, with smells, the pathway for incoming information is slightly different. Sensory information from smells bypasses the thalamus and heads straight for the olfactory bulb. The olfactory bulb is directly connected to the limbic system which consists of the amygdala and the hippocampus, and the bulb passes on the info to this system. This explains why certain scents trigger immediate emotional responses and/or memories. In fact, the principle of emotion and memory invoking through smell is the very basis of the perfume industry!
There is another interesting revelation which further supports this idea. A 2017 study conducted by Denise Manahan-Vaughan and Christina Strauch in Ruhr University [Germany] indicated that the olfactory bulb may also store memories itself. This phenomenon is due to the piriform cortex found in the olfactory bulb. The piriform cortex is connected to many parts of the brain, including the orbitofrontal cortex. Strauch and Manahan-Vaughan found that piriform cortex may actually serve as a long term memory archive, but only with instruction from orbitofrontal cortex: the part of the brain responsible for making judgements.
Through an evolutionary lense, the distinction in how smells are processed compared to the 4 other senses makes sense. One of the key ways in which many ancient organisms navigated and understood their surroundings was through smell. Many single celled organisms interacted with the surrounding chemicals and responded accordingly. Smell detection was a major advantage to many organisms, and has been developing for many years. This provides a reasonable idea to why humans have only 4 types of light and 4 types of touch receptors, while we have thousands of smell receptors.
Pragmatically, the reason scents invoke intense memories is because the location of brain scent info is sent to (the olfactory bulb) is directly connected to the memory center of the brain (the hippocampus) and the emotion processing sector (the amygdala).
So, the next time the smell of your skates bring back memories of your figure skating championship, or the whiff of popcorn revives your first date, enjoy the memories which come along with the specific wiring of your brain!
Holohan, Meghan. “Smells like Nostalgia: Why Do Scents Bring Back Memories?” NBCNews.com, NBCUniversal News Group, 19 July 2012, http://www.nbcnews.com/healthmain/smells-nostalgia-why-do-scents-bring-back-memories-895521.
“Psychology and Smell.” Fifth Sense, http://www.fifthsense.org.uk/psychology-and-smell/.
Strauch, Christina, and Denise Manahan-Vaughan. “In the Piriform Cortex, the Primary Impetus for Information Encoding through Synaptic Plasticity Is Provided by Descending Rather than Ascending Olfactory Inputs.” OUP Academic, Oxford University Press, 24 Nov. 2017, academic.oup.com/cercor/article/28/2/764/4656154.
Urry, Lisa A, et al. Campbell Biology. 11th ed., Pearson.
Walsh, Colleen. “How Scent, Emotion, and Memory Are Intertwined – and Exploited.” Harvard Gazette, Harvard Gazette, 27 Feb. 2020, news.harvard.edu/gazette/story/2020/02/how-scent-emotion-and-memory-are-intertwined-and-exploited/.