Hi there, internet.
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: “Why do
you stop noticing smells after a while?”
They’re still there.
Why does your brain tell you that they’re
not?
The “why” is actually simple.
Experts in biology and psychology and volatile
aroma compound physics (aka 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.
Sharp, “gross” scents may indicate that
a dangerous predator is in the area, or that
there’s a disease at work, or that the thing
you’re about to eat should under no circumstances
be eaten.
If you stick around a particular scent, your
brain figures it’s already done warned you
about that one and thus frees up its processing
power for logging new scents and changes in
scent intensity.
This is called olfactory adaptation.
How your brain accomplishes this type of sensory
adaptation is more complicated.
When you notice a smell, a molecule of a volatile
aroma compound (that is, a gaseous, smelly
thing) has entered your nose.
Our nasal passages are lined with somewhere
around 10 million neurons.
You can think of each of those neurons as
a tiny tree designed to pick up on a single
type of scent.
They have branches called dendrites, each
covered in smaller structures (like leaves,
going with the tree concept) that are called
cilia.
The cilia are studded with odor receptors.
A molecule -- of whatever kind of scent that
neuron specializes in sensing -- can bind
to each receptor.
When that binding happens, it sets off an
electrochemical chain reaction.
In the end, the neuron sends an electrical
impulse through its axon (metaphorically,
its root), up into your olfactory bulb.
That’s the part of your brain that processes
scent stimuli and sends the information on
to other parts of the brain.
Very basically, the more molecules that bind
to a given 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 scent’s presence within
a few breaths.
Researchers think that there are a couple
things going on here.
First, in those tree-like neurons in your
nose, at least one chemical plays double-duty
in both helping send electrical impulses to
the brain and in stopping those electrical
impulses.
The culprit here seems to primarily be calcium
ions, if you were curious.
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 what's
going on here, but we do know it happens because
they’ve conducted experiments where they’ve
only exposed only one nostril to a scent.
Neurons in the other nostril start adapting
to it.
But there are more questions here.
How do different scents and different lengths
of exposure lead to different adaptations?
Why can you never smell your own home the
way other people experience it?
“Shenanigans” is the answer science has
to give us right now.
Because the perception of scent isn’t just
physical; it’s psychological.
What the other parts of your brain do with
the scent information that the olfactory bulb
sends them absolutely factor in, in ways that
researchers are still trying to suss out.
So that (sort of) wraps up today’s question.
My question for you: What scents do you like
and hate?
We’ve got a really good debate about gasoline
going in another video’s comment thread.
I’m a bit of a perfume fanatic myself, though
my very favorite scent may be bread baking.
Let me know in the comments, like and subscribe
if you learned something, and for lots more
like this, head on over to HowStuffWorks.com.
