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Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,

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Speaker 1: I'm Lauren Vogelbaum, and I'm here today to tell you

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Speaker 1: that your brain lies to you, not maliciously. It thinks

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

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Speaker 1: Why do you stop noticing smells after a while? They're

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

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Speaker 1: The y is actually simple. Experts in biology, psychology, and

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Speaker 1: volatile aroma compound physics a k a. The science of

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Speaker 1: smells all pretty much agree that you stop noticing a

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Speaker 1: smell after a short while because your brain wants to

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Speaker 1: concentrate on scanning for new and potentially hazardous smells. That's

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Speaker 1: because sharp gross sense may indicate the dangerous predators in

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Speaker 1: the area, or that there's a diseased work, or that

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Speaker 1: the thing that you're about to eat should, under no

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Speaker 1: circumstances be eaten. But if you stick around a particular scent,

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

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Speaker 1: and thus freese up its processing power for logging new

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Speaker 1: sense and changes in scent intensity. This is called olfactory adaptation.

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Speaker 1: How your brain accomplishes this type of sensory adaptation is

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Speaker 1: more complicated. When you notice a smell, a molecule of

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Speaker 1: volatile aroma compound, that is, a gaseous smelly thing has

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Speaker 1: entered your nose. Our nasal passages are lined with somewhere

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Speaker 1: around ten million neurons. You can think of each of

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Speaker 1: those neurons as a tiny tree designed to pick up

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Speaker 1: on a single type of scent. They have branches called dendrites,

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Speaker 1: each covered in smaller structures that are called cilia and

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Speaker 1: are kind of like leaves. Going with the tree concept,

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Speaker 1: the cilia are studied with odor receptors. A molecule of

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Speaker 1: whatever kind of scent that neuron tree specializes in sensing

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Speaker 1: combined to each odor receptor. When that binding happens, it

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Speaker 1: sets off an electrochemical chain reaction. In the end, the

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

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Speaker 1: route up to the olfactory bulb in your brain. That's

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Speaker 1: the part of your brain that processes scent stimuli and

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Speaker 1: sends the information on to other parts of your brain.

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Speaker 1: Very basically, the more molecules that bind to a given

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Speaker 1: type of scent receptor throughout your nasal passages, the stronger

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Speaker 1: the signal to your brain will be and the stronger

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Speaker 1: you will perceive the scent to be. But we can

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Speaker 1: adapt to a sense presence within a few breaths. Researchers

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

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Speaker 1: in those tree like neurons in your nose, at least

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Speaker 1: one bodily chemical calcium ions to be specific, plays double duty.

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Speaker 1: It both helps send electrical impulses to the brain and

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Speaker 1: helps stop those electrical impulses. After a few molecules have

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Speaker 1: bound themselves to the scent receptors on these cilia leaves

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Speaker 1: of a given neuron, chemicals from that electrochemical chain reaction

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Speaker 1: start building up in the neuron. Although they usually make

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Speaker 1: impulses happen, their build up will prevent the neuron from

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Speaker 1: sending further impulses to the brain for a while. The

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Speaker 1: second thing going on here is that there's some kind

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Speaker 1: of feedback loop among your nasal neurons and your olfactory bulb.

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Speaker 1: Researchers aren't precisely sure how it works, but we know

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Speaker 1: what happens because they've conducted experiments where they've exposed only

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Speaker 1: one nostril to assent neurons in the other nostril will

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Speaker 1: start adapting to it. But there are more questions here.

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Speaker 1: How do different sense and different lengths of exposure lead

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Speaker 1: to different adaptations? Why can you never smell your own

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Speaker 1: home the way that other people experience it. The answer

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Speaker 1: science has to give us right now is basically shenanigans,

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

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Speaker 1: What other parts of your brain do with the scent

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Speaker 1: information that the olfactory bulb sends them absolutely factors in

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Speaker 1: and in ways that researchers are still trying to suss out.

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Speaker 1: Today's episode was written by me Weird and produced by

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Speaker 1: Tyler Clang. I'm supposed to remind you to contain yourself

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Speaker 1: in brain stuff themed t shirts from our online shop

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Speaker 1: at t public dot com slash brain stuff, and of course,

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Speaker 1: for lots more on this and other topics that won't

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Speaker 1: fade into the background, visit our home planet, how stuff

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Speaker 1: Works dot com