Why Do You Stop Noticing Scents After a While?

Smells seem to disappear after a while because our brains lie to us. Not maliciously -- they think they're helping. Learn about olfactory adaptation in this episode of BrainStuff.

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Episode Transcript

Speaker 1 (00:02):
Welcome to brain Stuff from How Stuff Works. Hey, brain Stuff,
I'm Lauren Vogelbaum, and I'm here today to tell you
that your brain lies to you, not maliciously. It thinks
it's helping, Which brings us to our question of the day.
Why do you stop noticing smells after a while? They're
still there? Why does your brain tell you that they're not?

(00:24):
The y is actually simple. Experts in biology, psychology, and
volatile aroma compound physics a k a. The science of
smells all pretty much agree that you stop noticing a
smell after a short while because your brain wants to
concentrate on scanning for new and potentially hazardous smells. That's
because sharp gross sense may indicate the dangerous predators in

(00:48):
the area, or that there's a diseased work, or that
the thing that you're about to eat should, under no
circumstances be eaten. But if you stick around a particular scent,
your brain figures it's already done warned you about that one,
and thus freese up its processing power for logging new
sense and changes in scent intensity. This is called olfactory adaptation.

(01:09):
How your brain accomplishes this type of sensory adaptation is
more complicated. When you notice a smell, a molecule of
volatile aroma compound, that is, a gaseous smelly thing has
entered your nose. Our nasal passages are lined with somewhere
around ten million neurons. You can think of each of
those neurons as a tiny tree designed to pick up

(01:31):
on a single type of scent. They have branches called dendrites,
each covered in smaller structures that are called cilia and
are kind of like leaves. Going with the tree concept,
the cilia are studied with odor receptors. A molecule of
whatever kind of scent that neuron tree specializes in sensing
combined to each odor receptor. When that binding happens, it

(01:53):
sets off an electrochemical chain reaction. In the end, the
neurons sends an electrical impulse through its action. Metaphorically, it's
route up to the olfactory bulb in your brain. That's
the part of your brain that processes scent stimuli and
sends the information on to other parts of your brain.
Very basically, the more molecules that bind to a given

(02:14):
type of scent receptor throughout your nasal passages, the stronger
the signal to your brain will be and the stronger
you will perceive the scent to be. But we can
adapt to a sense presence within a few breaths. Researchers
think that there are a couple of things going on here. First,
in those tree like neurons in your nose, at least
one bodily chemical calcium ions to be specific, plays double duty.

(02:38):
It both helps send electrical impulses to the brain and
helps stop those electrical impulses. After a few molecules have
bound themselves to the scent receptors on these cilia leaves
of a given neuron, chemicals from that electrochemical chain reaction
start building up in the neuron. Although they usually make
impulses happen, their build up will prevent the neuron from

(03:00):
sending further impulses to the brain for a while. The
second thing going on here is that there's some kind
of feedback loop among your nasal neurons and your olfactory bulb.
Researchers aren't precisely sure how it works, but we know
what happens because they've conducted experiments where they've exposed only
one nostril to assent neurons in the other nostril will

(03:21):
start adapting to it. But there are more questions here.
How do different sense and different lengths of exposure lead
to different adaptations? Why can you never smell your own
home the way that other people experience it. The answer
science has to give us right now is basically shenanigans,
because the perception of scent isn't just physical, it's psychological.

(03:44):
What other parts of your brain do with the scent
information that the olfactory bulb sends them absolutely factors in
and in ways that researchers are still trying to suss out.
Today's episode was written by me Weird and produced by
Tyler Clang. I'm supposed to remind you to contain yourself

(04:05):
in brain stuff themed t shirts from our online shop
at t public dot com slash brain stuff, and of course,
for lots more on this and other topics that won't
fade into the background, visit our home planet, how stuff
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