How Smell Triggers Memories

 Odor has been shown to trigger memory in a Harvard Medical School lab study on how animals utilize their senses to interpret the environment. The article describes how our ancient ancestors used their sense of smell to map out their environment and recall past locations. The relationship between olfactory sensory neurons in the brain, which provide electrical impulses to various regions of the brain through axons, and human noses' odor receptors is demonstrated by physiology.

 These signals travel to multiple parts of the brain that are involved in learning, emotion, and memory. The olfactory, or piriform cortex, identifies smells; the amygdala, which generates emotion; and the hippocampus, stores and organizes memories. The hippocampus can file and preserve information forever if it believes that the smell is significant, for example, if it is associated with a very emotional occasion. The same smell might evoke strong memories and emotional resonance decades after the event.

The thalamus of the brain is the first region that sights, sounds, and other sensory data must pass through in order to reach the amygdala and hippocampus. On the other hand, the information is explained to the memory and emotion centers via the olfactory system, which is located directly next to them. I found it fascinating that this could be the reason behind research showing that odor-evoked memories are more likely to be emotional and to date back further in life than memories induced by other senses.

Reference: 
https://magazine.hms.harvard.edu/articles/connections-between-smell-memory-and-health