The smell of a newly mowed lawn may take back to your childhood days tumbling in the backyard. Maybe catching a whiff of a certain perfume instantly reminds you of your mom.
Why do smells have the power to trigger such strong memories? The answer is in your brain.
The amygdala is the structure in the brain's temporal lobe that plays an important role in processing emotions. It sits right near the hippocampus, which is responsible for learning and forming memories, according to the University of Queensland Brain Institute. Both elements are part of the brain's limbic system, which also includes the thalamus, the brain's communication or relay station.
Normally, when you hear, see, touch or taste something, that information goes to the thalamus. It then sends it to the important areas in the brain, including the amygdala and hippocampus.
But it's a whole different ballgame with smells. They skip the thalamus and head right to the olfactory bulb, which helps the brain process odors. The olfactory bulb is directly connected to the amygdala and hippocampus, Curiosity points out.
This immediate link might explain why a smell can instantly trigger a vivid memory. Although humans are so visually oriented, it's interesting that smells would have such an impact in the brain.
"Some think it goes back to the way we evolved: Smell is one of the most rudimentary senses with roots in the way single-celled organisms interact with the chemicals around them, so it has the longest evolutionary history," writes Curiosity's Ashley Hamer. "This also might explain why we have at least 1,000 different types of smell receptors but only four types of light sensors and about four types of receptors for touch."
Emotions, not memories
Interestingly, sometimes a smell will trigger strong emotions, but you may not actually recall the memory behind those feelings.
Sometimes the memory behind the emotional response never resurfaces. You just feel the feelings of whatever happened, but don't remember what you experienced, Rachel Herz, an adjunct assistant professor of psychiatry and human behavior at Brown University in Rhode Island, tells LiveScience.
This is sometimes due to lack of context.
If you smell a long-lost scent when you're walking down the street and it's something you used to smell in your home growing up, for example, it will be difficult to place because you're experiencing it in a different situation. You'll still feel an emotional rush, but you might not have the associated memories.
The brain uses the context "to give meaning to the information" and find that memory, Herz explains.
Words versus smells
Researchers have found that smells invoke more memories than the words that describe those smells. For example, the scent of a freshly baked apple pie might immediately zip you back to your grandmother's kitchen. But just hearing someone say "apple pie," might not give you the same trip down memory lane.
In one study published in the journal Neuropsychologia, researchers found that memories triggered by a scent resulted in much more activity in the brain's limbic system than memories accompanied by just a word without any accompanying smell. So, for example, people responded much more emphatically when they smelled a rose than when they just heard the word "rose."
Merely hearing the word didn't conjure up the emotional response and memories as the immediate visceral reaction triggered by the scent.
"Smells do bring back memories," Dr. Ken Heilman, professor of neurology and health psychology at the University of Florida, tells NBC News. "Smell goes into the emotional parts of the brain and the memory parts, whereas words go into thinking parts of the brain."