WEBVTT - Why Do You Stop Noticing Scents After a While?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,

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<v Speaker 1>I'm Lauren Vogelbaum, and I'm here today to tell you

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<v Speaker 1>that your brain lies to you, not maliciously. It thinks

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<v Speaker 1>it's helping, Which brings us to our question of the day.

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<v Speaker 1>Why do you stop noticing smells after a while? They're

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<v Speaker 1>still there? Why does your brain tell you that they're not?

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<v Speaker 1>The y is actually simple. Experts in biology, psychology, and

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<v Speaker 1>volatile aroma compound physics a k a. The science of

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<v Speaker 1>smells all pretty much agree that you stop noticing a

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<v Speaker 1>smell after a short while because your brain wants to

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<v Speaker 1>concentrate on scanning for new and potentially hazardous smells. That's

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<v Speaker 1>because sharp gross sense may indicate the dangerous predators in

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<v Speaker 1>the area, or that there's a diseased work, or that

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<v Speaker 1>the thing that you're about to eat should, under no

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<v Speaker 1>circumstances be eaten. But if you stick around a particular scent,

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<v Speaker 1>your brain figures it's already done warned you about that one,

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<v Speaker 1>and thus freese up its processing power for logging new

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<v Speaker 1>sense and changes in scent intensity. This is called olfactory adaptation.

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<v Speaker 1>How your brain accomplishes this type of sensory adaptation is

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<v Speaker 1>more complicated. When you notice a smell, a molecule of

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<v Speaker 1>volatile aroma compound, that is, a gaseous smelly thing has

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<v Speaker 1>entered your nose. Our nasal passages are lined with somewhere

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<v Speaker 1>around ten million neurons. You can think of each of

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<v Speaker 1>those neurons as a tiny tree designed to pick up

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<v Speaker 1>on a single type of scent. They have branches called dendrites,

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<v Speaker 1>each covered in smaller structures that are called cilia and

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<v Speaker 1>are kind of like leaves. Going with the tree concept,

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<v Speaker 1>the cilia are studied with odor receptors. A molecule of

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<v Speaker 1>whatever kind of scent that neuron tree specializes in sensing

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<v Speaker 1>combined to each odor receptor. When that binding happens, it

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<v Speaker 1>sets off an electrochemical chain reaction. In the end, the

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<v Speaker 1>neurons sends an electrical impulse through its action. Metaphorically, it's

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<v Speaker 1>route up to the olfactory bulb in your brain. That's

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<v Speaker 1>the part of your brain that processes scent stimuli and

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<v Speaker 1>sends the information on to other parts of your brain.

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<v Speaker 1>Very basically, the more molecules that bind to a given

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<v Speaker 1>type of scent receptor throughout your nasal passages, the stronger

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<v Speaker 1>the signal to your brain will be and the stronger

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<v Speaker 1>you will perceive the scent to be. But we can

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<v Speaker 1>adapt to a sense presence within a few breaths. Researchers

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<v Speaker 1>think that there are a couple of things going on here. First,

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<v Speaker 1>in those tree like neurons in your nose, at least

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<v Speaker 1>one bodily chemical calcium ions to be specific, plays double duty.

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<v Speaker 1>It both helps send electrical impulses to the brain and

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<v Speaker 1>helps stop those electrical impulses. After a few molecules have

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<v Speaker 1>bound themselves to the scent receptors on these cilia leaves

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<v Speaker 1>of a given neuron, chemicals from that electrochemical chain reaction

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<v Speaker 1>start building up in the neuron. Although they usually make

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<v Speaker 1>impulses happen, their build up will prevent the neuron from

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<v Speaker 1>sending further impulses to the brain for a while. The

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<v Speaker 1>second thing going on here is that there's some kind

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<v Speaker 1>of feedback loop among your nasal neurons and your olfactory bulb.

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<v Speaker 1>Researchers aren't precisely sure how it works, but we know

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<v Speaker 1>what happens because they've conducted experiments where they've exposed only

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<v Speaker 1>one nostril to assent neurons in the other nostril will

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<v Speaker 1>start adapting to it. But there are more questions here.

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<v Speaker 1>How do different sense and different lengths of exposure lead

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<v Speaker 1>to different adaptations? Why can you never smell your own

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<v Speaker 1>home the way that other people experience it. The answer

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<v Speaker 1>science has to give us right now is basically shenanigans,

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<v Speaker 1>because the perception of scent isn't just physical, it's psychological.

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<v Speaker 1>What other parts of your brain do with the scent

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<v Speaker 1>information that the olfactory bulb sends them absolutely factors in

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<v Speaker 1>and in ways that researchers are still trying to suss out.

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<v Speaker 1>Today's episode was written by me Weird and produced by

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<v Speaker 1>Tyler Clang. I'm supposed to remind you to contain yourself

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<v Speaker 1>in brain stuff themed t shirts from our online shop

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<v Speaker 1>at t public dot com slash brain stuff, and of course,

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