Speaker 1: Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,
Speaker 1: I'm Lauren Vogelbaum, and I'm here today to tell you
Speaker 1: that your brain lies to you, not maliciously. It thinks
Speaker 1: it's helping, Which brings us to our question of the day.
Speaker 1: Why do you stop noticing smells after a while? They're
Speaker 1: still there? Why does your brain tell you that they're not?
Speaker 1: The y is actually simple. Experts in biology, psychology, and
Speaker 1: volatile aroma compound physics a k a. The science of
Speaker 1: smells all pretty much agree that you stop noticing a
Speaker 1: smell after a short while because your brain wants to
Speaker 1: concentrate on scanning for new and potentially hazardous smells. That's
Speaker 1: because sharp gross sense may indicate the dangerous predators in
Speaker 1: the area, or that there's a diseased work, or that
Speaker 1: the thing that you're about to eat should, under no
Speaker 1: circumstances be eaten. But if you stick around a particular scent,
Speaker 1: your brain figures it's already done warned you about that one,
Speaker 1: and thus freese up its processing power for logging new
Speaker 1: sense and changes in scent intensity. This is called olfactory adaptation.
Speaker 1: How your brain accomplishes this type of sensory adaptation is
Speaker 1: more complicated. When you notice a smell, a molecule of
Speaker 1: volatile aroma compound, that is, a gaseous smelly thing has
Speaker 1: entered your nose. Our nasal passages are lined with somewhere
Speaker 1: around ten million neurons. You can think of each of
Speaker 1: those neurons as a tiny tree designed to pick up
Speaker 1: on a single type of scent. They have branches called dendrites,
Speaker 1: each covered in smaller structures that are called cilia and
Speaker 1: are kind of like leaves. Going with the tree concept,
Speaker 1: the cilia are studied with odor receptors. A molecule of
Speaker 1: whatever kind of scent that neuron tree specializes in sensing
Speaker 1: combined to each odor receptor. When that binding happens, it
Speaker 1: sets off an electrochemical chain reaction. In the end, the
Speaker 1: neurons sends an electrical impulse through its action. Metaphorically, it's
Speaker 1: route up to the olfactory bulb in your brain. That's
Speaker 1: the part of your brain that processes scent stimuli and
Speaker 1: sends the information on to other parts of your brain.
Speaker 1: Very basically, the more molecules that bind to a given
Speaker 1: type of scent receptor throughout your nasal passages, the stronger
Speaker 1: the signal to your brain will be and the stronger
Speaker 1: you will perceive the scent to be. But we can
Speaker 1: adapt to a sense presence within a few breaths. Researchers
Speaker 1: think that there are a couple of things going on here. First,
Speaker 1: in those tree like neurons in your nose, at least
Speaker 1: one bodily chemical calcium ions to be specific, plays double duty.
Speaker 1: It both helps send electrical impulses to the brain and
Speaker 1: helps stop those electrical impulses. After a few molecules have
Speaker 1: bound themselves to the scent receptors on these cilia leaves
Speaker 1: of a given neuron, chemicals from that electrochemical chain reaction
Speaker 1: start building up in the neuron. Although they usually make
Speaker 1: impulses happen, their build up will prevent the neuron from
Speaker 1: sending further impulses to the brain for a while. The
Speaker 1: second thing going on here is that there's some kind
Speaker 1: of feedback loop among your nasal neurons and your olfactory bulb.
Speaker 1: Researchers aren't precisely sure how it works, but we know
Speaker 1: what happens because they've conducted experiments where they've exposed only
Speaker 1: one nostril to assent neurons in the other nostril will
Speaker 1: start adapting to it. But there are more questions here.
Speaker 1: How do different sense and different lengths of exposure lead
Speaker 1: to different adaptations? Why can you never smell your own
Speaker 1: home the way that other people experience it. The answer
Speaker 1: science has to give us right now is basically shenanigans,
Speaker 1: because the perception of scent isn't just physical, it's psychological.
Speaker 1: What other parts of your brain do with the scent
Speaker 1: information that the olfactory bulb sends them absolutely factors in
Speaker 1: and in ways that researchers are still trying to suss out.
Speaker 1: Today's episode was written by me Weird and produced by
Speaker 1: Tyler Clang. I'm supposed to remind you to contain yourself
Speaker 1: in brain stuff themed t shirts from our online shop
Speaker 1: at t public dot com slash brain stuff, and of course,
Speaker 1: for lots more on this and other topics that won't
Speaker 1: fade into the background, visit our home planet, how stuff
Speaker 1: Works dot com