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SciShow explains how smells can bring back early memories -- even memories that your brain didn’t know you had.

Hosted by: Hank Green
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(SciShow Intro plays)

Hank: You're walking through a hardware store one day, when all of a sudden, you catch a whiff of something you haven't smelled in years.  Somehow, the scent of glue immediately takes you back to your Kindergarten classroom and you spend the next couple of minutes wondering what happened to that kid who used to eat all that paste.  You just experienced what's known as 'odor-evoked autobiographical memory'.  To put it simply, a smell made you remember something from your past, and it happened because of the way smells and memories are hardwired into your brain.  

Now, lots of different cues, like sights or sounds or even someone describing something or telling a story unrelated to your story, they can trigger memories.  But memories linked to smells are often stronger and more vivid, and studies have shown that they also tend to be memories of your early life, often before you were ten years old.  Which is weird, because adults usually experience what's known as a reminiscence bump, where they don't remember much from before their adolescence.  But smells are really good at bringing those memories back.  These memories tend to be more perceptual rather than conceptual, so you remember a particular sensation rather than a bunch of facts about something that happened, and researchers have come up with some theories why memories triggered by smells are so odd.

There's a big difference between the way your body handles sight, sound, taste, and touch, and the way it processes smells.  Those other senses are all routed through the thalamus, the part of your brain that sends them off into the appropriate processing centers.  But smells bypass all that.  Once they're detected by receptors in your nose, the signal heads straight to your olfactory bulb, the smell analyzing region in your brain.  And that area happens to be connected to the amygdala and the hippocampus, which are parts of the brain that help handle memory and emotion.  So it's possible that when you smelled that glue in Kindergarten, the signal got tangled up with memories of building blocks and apple juice, and when you smelled it again later, you remembered not just the glue, but also some of the associated memories, like that weird kid who ate the paste. 

In 2013, a group of European psychologists tested this whole phenomenon using Functional Magnetic Resonance Imaging.  First, they presented the subjects with 20 different strong, specific odors, like garlic, whiskey, and leather.  Then, for each person, they identified the two that elicited the oldest positive memories.  Then, it was time to scan their brains.  Each subject was presented with their two experimental smells, plus two generic control smells, flowers and citrus.  They were also shown some verbal cues, which were just the names of the smells projected onto a screen.  The researchers found that both types of triggers tended to activate the regions of the brain associated with memory, but while the verbal cues lit up parts of the brain that were responsible for processing smells, the smells themselves were more strongly connected to emotional processing centers.  Some of the participants associated the smells with memories from before they were ten, while others remembered things from when they were between ten and twenty.  And depending on which time frame the memories fell into, their brains tended to use different regions to recall them.  The earlier memories lit up the orbitofrontal cortex, which is connected to perception.  The later ones, on the other hand, tended to activate the left inferior front gyrus, which handles more conceptual memories.  

So, can you use your nose's superpowers to help you remember things for your next big exam?  Probably not.  Smells tend to evoke early perceptive memories of events, not concepts.  So the scent of glue might make you remember playing with construction paper in Kindergarten, but your smell memory will not help you memorize Maxwell's equations. 

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