The Scent of Cognition

We are enrobed in a world of scent, and as we know it's a heady powerful one -- with the power to make and summon memories. But this power is far more deep-seated in the brain than we previously thought. The ability to smell may even be root our ability to think.

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Episode Transcript

Speaker 1 (00:03):
Welcome to Stuff to Blow Your Mind from how Stuff
Works dot com. Hey, welcome to Stuff to Blow your Mind.
My name is Robert Lamb and I'm Julie Douglas. You know,
we've spent a lot of time on this podcast talking
about the senses, breaking down the senses and getting down
to not only the scientific underpinnings of our sense experience,

(00:26):
but also the sort of mysteries of it that we
take for granted every day. That's true, and uh sent
is one of those things that we often take for granted,
but it turns out to be the hum dinger of
the senses. And we're going to talk about that today.
And we thought, well, heck, while we're rolling out sense
and smells, we might as well roll out a little proost. Yeah.

(00:48):
Marcel Proust eighteen seventy one through French novelist, critic and says,
best known for his novel In Search of Lost Time
a k a. The Remembrance of Things Past. Yes, because
in this novel he has what is now known as
the Proust moment, this sort of memory that is evoked
by a food and in particular scent, which is as

(01:10):
we know, bound up with food. Now This is him
describing the shell shaped cookie called Madeline. He says, quote,
I raised to my lips a spoonful of the tea
in which I had soaked a morsel of the cake.
No sooner had the warm liquid mixed with the crumbs
touched my palette than a shutter ram through me, and
I stopped intent upon the extraordinary thing that was happening

(01:33):
to me. An exquisite pleasure invaded my senses. M hmm.
You know, I think we we've all had those moments
in our lives where some some scent or some taste
associated with the scent, uh finds. Maybe we're just walking
down the street and it just we end up just
time traveling in our mind back to some some moment
in the past that we we maybe don't even think

(01:55):
about all that often, you know, and we tend to
not even think about how it's acting on our behavior.
We've brought this up before. There was a study on
altruism and freshly baked bread, and I won't go into
that because it's it's a bit lengthy, but basically, people
who were smelling the scent, we're much more inclined to

(02:16):
help other people. Yeah, uh, Now, Prost goes on to
to to summarize things a little bit, and he says,
when nothing else subsists from the past, after the people
are dead, after the things are broken and scattered, the
smell and taste of things remain poised for a long time,
like souls bearing resiliently on tiny and almost impalpable drops

(02:39):
of their essence. The immense edifice of memory. Indeed, and
that is that's the sort of thing that's behind the
wall of smell, And that's what we're gonna look at today. Yeah,
it is weird, how like even the most comforting smells
in the world, you know, the smell of you know,
of a loved one's hair or skin, or or you know,
just the sort of house smells that that give you

(02:59):
that warn't feeling inside of yourself, well you know, your
favorite to meal, what have you? Something with you with
rich connections. They're not something that you end up just
craving all the time. But but it's only when you
actually encounter them that you that they really take hold. Yeah,
because it's light taking a book off the shelf of memory. Now,
before we kind of get into these more specifics of

(03:22):
memory and smell, let's look at a little cent one
oh one, because think about all of these possible smell surrounding.
You might say possible, because this sense have to be
volatile enough to spew out microscopic particles in the air
and then get on your noses radar system. Right. Um,
so your kitchen countertops or even this table that we're

(03:45):
podcasting at that is not a volatile material. But let's
say nol our producer brings in a little bit of
warmed over cabbage. Then all of a sudden, that is
a huge volatile funk. Now. In the book A Natural
History of the Sense of by Diane Ackerman, she writes, quote,
each day, we breathe about twenty three thousand, forty times

(04:05):
and move around four hundred and thirty eight cubic feet
of air. It takes us about five seconds to breathe,
two seconds to inhale, and three seconds to exhale. And
in that time molecules of odor flood through our systems.
Inhaling and exhaling, we smell odors. Smells code us, swirl
around us and enter our bodies, emanate from us. We

(04:27):
live in a constant wash of them. And get this,
this is really interesting According to research by Stanford University scientists,
which was published in a November fourth issue of Nature,
each nostril of the human nose is tuned to smell
some odors better than others, and the specialization moves back

(04:50):
and forth from one nostril to the other, so one
a certain smell might be more of a left nostril
smell as opposed to a right nostril smell. Yeah. So
there's turns out that there's a difference in airflow of
nostrils and that effects scent detection, which kind of gets
you to the question maybe you never even wondered about
why do we have two nostrils anyway? Yeah, well it

(05:12):
turns out there's two different systems detecting different odors. Huh. Yeah.
I was kind of, without really thinking about it, thought
it was just so that if snot clogged up one,
you still had another one. You know. It's kind of
like having a double barrel shotgun. Right. Indeed, all right, so,
as we've discussed, you have these airborne molecules peeling off
of things. A lot of molecules peeling off of something

(05:32):
like freshly baked pie. Uh, not so much with say
a lump of steel. Okay. So these molecules are floating around,
they enter the nostrils and then they hit the olfactory
epithelium is the center of the of olfactory sensation. Now
it takes up we're talking about a mirror one square
inch of the superior portion of the nasal cavity. Mucas

(05:55):
coats the epithelium surface and it helps dissolve these odorance
so they can all they gonna be properly uh taken in. Okay,
Then these highly specialized olfactory receptor cells come into play. Uh.
These are neurons with knob shaped tips called dendrites and
old factory here's that bind with the odorants cover each
of these dent drives. Next, with the odorant having successfully

(06:17):
stimulated the receptor cell, the cell send an electrical impulse
to the old factory bulb. And that is part of
the brain's limbic system. That's gonna be key here in
a moment because of the olympic systems relationship to memory. Okay. Now, specifically,
each olfactory receptor type sends its electrical impulse to a
particular microregion of the olfactory bulb. So we've gone from

(06:40):
molecule on on all the way up into the brain.
And then this is where the sensation of smell as
we experience it uh in our minds emerges. Now to
underscore how important smell is, let me just point out
that if you destroy a neuron in the brain, it's
finished forever. It won't regrow. If you damage neurons and
your or eyes or ears, both organs will be irreparably damaged.

(07:04):
But the neurons and the nose uh, those are replaced
about every thirty days. And according to Diane Ackerman, unlike
any other neurons in the body, they stick right out
and wave in the air current like animonees on a
coral reef. And I thought this is such a great
similar especially if you consider some research that was done

(07:26):
by the Cavalry Institute for Systems Neuroscience. They found that
when it came to scent, there are synchronized brain waves
of twenty to forty hurts moving through the brain and
these are signals from the nose that translate and they
connect to memories in this sort of orchestrated symphony of
signals in your brain. And the reason they know that,

(07:48):
of course is rats. Because we've discussed in an earlier
episode to give us a good amount of information about
these types of things and systems in the brain. Now,
the researchers took seen to twenty electrodes. They place them
in the hippocampus in the different areas of the into
rhinal cortex and rats, and this allowed them to observe

(08:08):
this wave like action and synchronousity happening during the scent
memory acquisition in rats. Now I mentioned that the olfactory
bulb is part of the brain's limbic system, again area
associated with memory and feeling. That the bulb has intimate
access to the amygla, which processes emotion in the hippocampus,
which is responsible for associative learning. And this this is key, okay,

(08:32):
because it's why smell can call up those memories and
powerful responses almost instantaneously, cutting out we're almost cutting out conscience, remembrance.
And the key triggers here are conditioned responses. You smell
something and this links to an event, person, thing, or moment.
The brain forges the link between smell and memory, and

(08:52):
then when you smell it again, even years later, decades later,
the link is already there lights up again. Now, since
we encounter most of these new odors in our youth,
because I mean, you know, there are a lot of
smells out there, but you're gonna hit something. Most of
the key ones, you know pretty early on, since you
smell most of them in your youth. Smells often some
of these strong feelings of nostalgia, mental time travel, taking

(09:14):
us back to bake pies of our youth, or or
even it's not even necessarily a positive, you know, or
at least subjectively positive smell that we end up having
these positive associations with. Uh. It could be something like
chlorine in a pool, something that is harsh chemical uh.
And to some people with a different association, and they

(09:35):
might they might not have the same kind of positive
swelling of emotion around it. But once that's forged in
the brain, that's the connection we take when we smell
it again. Uh. And interestingly enough, we even begin making
these emotional connections to smells before we're even born. Infants
who have been exposed to alcohol, cigarette smoke, or garlic
in the womb actually show a preference for these smells

(09:57):
later on. And that's really interesting of her. Before that, Um,
some of your food choices can influence the diet of
your child later on. But who knew that even smoke
would be something that would be incorporated into the landscape
of smell for an infant um. Now we're going to
take a quick break. When we get back, we are

(10:18):
going to look at how smell influenced the formation of
the primitive brain. All right, we're back. We're talking about smell.
We're talking about and be a very primal sense, if
not the most primal sense. Yeah, and if you veer
away from humans for a moment and you look at

(10:40):
smell and its role in the animal world, will you
see that it becomes maybe ten or fifteen episodes spirhirling
out of this. So we're not going to go way
deep into this, but we wanted to mention some of
the ways that sensory world is interacting um with scent
in organisms. And that's because it really plays a bigger role,

(11:02):
a more integral role in identification and communication. So, for instance,
if you think about a tobacco leaf that's being munched
on by a caterpillar, well, that tobacco leaf will emit
something called a green leaf volatile and this is a
chemical that once it's airborne, it acts as a kind
of s o s two predators of the caterpillar, like wasps,

(11:26):
and it's essentially saying to those wops, hey, there's something
there's there's this blood sucker on me or this you know,
leaf sucker on me, and it is completely distracted right now.
And I know you love a good juicy caterpillar to
swoop down and eat it. And that in and of
itself is amazing, this kind of chemical communication. But then
you consider the research that's been done on rodents, and

(11:50):
that we can see that rodents can actually detect fear
through scent alone, or even considering something like a silver
tip grizzly, which can smell a carcass up to eighteen
miles away, which would be really important to aggressively right
because that could be a second lunch, a second breakfast,
a snack, you know, any sort of leftovers. And these

(12:10):
are just just a tiny bit of examples of the
rich roll of scent in the animal world. But it
gets even more micro than that. Yeah, And and in
doing so, it gets even more telling about just this
idea of smell as this primary sense of the connection
between smell and survival, because in the you know, your

(12:31):
average day, we're not smelling out our dinner. We're not saying,
all right, you know, time to get some food on
the table, let me go stick my nose out in
the air. But we see this, we we see this
even in bacteria. According to a two thousand and ten
study from the University Medical Center Utrecht in the Netherlands, UH,
bacteria can detect ammonia. Ammonia is an important source of

(12:55):
nutrients for bacteria, and it causes bacteria to form slimy
colonies called bio films UH and smelling it. Identifying ammonia
may help the microbes to locate their food sources and
avoid competitors. Now, critics of this study, you know, easily say, well,
that's not smell. You're just you're you're talking about something
far more primitive. But if you break down smell, if

(13:17):
you define smell, it's just simply sensing a volatile molecule,
sensing key molecules that are peeling off. As as we
mentioned at the beginning, then that's exactly what's going on
with these bacteria. They're not smelling oxygen because it doesn't
have a smell. It's always there around them. But they
can smell an important gas that signals food, which I
think is really root to all animals, right, because this

(13:42):
is the simplest and most ancient form of life from
which everything else evolved. In this sort of food detection
device would really play into how the primitive brain would develop.
So Diane Ackerman's book, again, A Natural History of Senses,
goes into this. She writes that chemical detection was so
important that the scent sensitive tissue sitting atop the nerve

(14:03):
cord developed into a primitive brain. Moreover, and this is
probably the most mind blowing part of this. Our cerebral
hemispheres were originally buds from the old factory stocks. Huh.
So it's it's one of the prime primal scoops of
ice cream on which our our additional brain scoots were placed. Yeah,
I mean these are sort of the original blueprints, right.

(14:24):
That called back to this ability to detect detect chemicals
that is like the base stock of the brain here.
So much of it is fascinating, and that there's a
certain level of understanding that we have conscious understanding about
what's going on with our our sense of smell, and
then there's all this other stuff that's going on under
the surface. And a great example of This comes from

(14:45):
a two thousand and fourteen study from Manl Chemical Sensus Center. Uh,
show that that people can actually smell differences in dietary
fat in foods. In other words, the nose nose when
you try to pull a fast one on it with
oh fat alternatives. Yeah. So have this breakdown, well, eight
participants in two locations, Philadelphia and the Netherlands. Uh. And

(15:09):
that's key here because we're gonna be dealing with with
milk and uh, individuals in the Netherlands consume a lot
more milk than individuals in Philadelphia. Um, they have cream cheese.
Even that. Yeah, even though they have cream cheese. Uh,
the Netherlands are still they're still they're still coming out
on top, all right. So these participants, uh, they were
made to smell samples of milk with varying amounts of fat,

(15:33):
and they found that participants could actually distinguish among the
samples based on their fat content. And and really this
this makes perfect sense. It's that means as simple as this, fatty,
high calorie foods equal energy and energy equal survival. So
it makes perfect sense from evolutionary standpoint. You want to
be able to sniff out the best source of nutrients. Um.
Now it's not learned behavior, it's it's in bread behavior. UM.

(15:56):
I already mentioned that the Dutch drink more milk than Americans,
but both were equally good at sniffing out the fatty goodness. Likewise,
participant weight didn't play into the results either, and they
made sure that they were isolating just the fat by
using powdered milk rather than fresh. Now, there's still some
lingering questions here that the researchers are looking into. UM.

(16:18):
For starters, fat molecules and milk are not very volatile.
They don't peel off and float around as easily, and
therefore shouldn't be that easily smelled. But they think they
might be attaching to other compounds that are huh yeah,
especially powdered milk right, because it doesn't have anything to
help dissolve and create a vapor. UM. I think what
that points to to me is that humans ability to

(16:40):
suss out smell is you know, a little bit more
complex than we thought. I mean, not dog complex. We
don't have that kind of sensory world available to us,
but certainly a little bit more enhanced than we thought.
And I wanted to point to this idea um that
or this previous idea that it was thought that we
could sniff out about ten thousand smells. Well, in two

(17:03):
thousand and fourteen, researchers from the Rockefeller University and the
Howard Hughes Medical Institute put together an experiment that would
blow that ability to detect ten thousand smells out of
the water. And the researchers started with bottles of one
hundred and twenty eight distinct smells, so think about grass
or citrus, right, and they mixed up to thirty different

(17:26):
chemicals with it to create unfamiliar smells. And they did
that because they wanted to really obscure what it was
and really have people work with their sense of smell
to suss out what sort of chemicals or odors they
were sniffing. And so they took three bottles and two
of those bottles were the same and one was different
from it, and they had twenty six study participants quaffing

(17:50):
these odors. And what they did is they calculated the
percentage of these mixtures that participants could distinguish, and then
they handed that data over to a mathematician who figured
out the number of possible unique odors that could be
made from the mixtures of the chemicals. Okay, I'm gonna
guess it's it's no dan no, how many one trillion? Yeah,

(18:22):
So okay, here's the thing, though, this doesn't mean that
now one connoisseurs need to start using one trillion descriptors exists, right.
They are trying really hard, uh, but because this is
more about distinguishing rather than identifying the smells, and it's
really no indication that we're actually able to pick up

(18:45):
on a trillion smells, because you think about you may
not even be met with one trillion smells in your lifetime.
It's uh, it's more just that that that's the upper
limit of possible sense. And the reason why they did
this study is they wanted to discredit that idea of
tenos smells because it's from the early twentieth century and

(19:07):
it's not really tied to any specific data set. Is
just one of some one of those ideas that arose,
and so this was that, um, this was their chance
to say, no, smell is so much more complicated and
nuanced than that, and our ability to detect it. We've
been kind of given it short shrift for a while.

(19:27):
We have and uh, you know, I mean as far
as the senses go, you can sort of look at
our technology as a good, uh, a good way to
gauge how much emphasis we put on on it, right
because right now I can we either of us can
pick up our smartphone and we can we can send
visual information, we can send auditory information. We've discussed all
the different haptic technologies in place where we're we're a

(19:48):
lot of a lot of people are working really hard
on being able to transmit feeling and touch across the internet. Hugs,
We've talked about that. But but where's the smell, where's
the where's the stank? Well. On June fourteen, the first
ever transatlantic scent message was transmitted from New York City

(20:09):
to Paris, and Harvard professor David Edwards and his co
inventor Rachel Field. They they sent an image, an electronic
image tagged with a scent, to Le la Boutoire, a
contemporary art and design center in Paris, and they're a
device called an O phone decoded the message and reproduced

(20:29):
the scent using its aromatic cartridges. Yeah, and that the
scent message that is sent, by the way, is the
the scent email. If you will. The scent text message
is called an O note, just just to get the
lingo out there. UM. This uh, this is a technology
that is still very much in its infancy. Um. Basically

(20:50):
like where they are now with it is they're they're
they're looking at being able to capture somewhere in the
area of three thousand unique scents. Uh. And it's and
you'd have to go to an O phone hotspot to
pick one up if somebody sent one to you, Because
it ultimately gets into that area of printing smells, of
using primary odors as a palette, and then using combining

(21:11):
those to try and create at least an approximation of
what you're going for with what you're trying to scent.
And so the exciting part of this is that scent
could begin to be woven into uh, these different types
of media that we consume. And so right now we
have music right is being woven into the media that

(21:32):
we enjoy, and a lot of times we don't think
about how powerful that is. That even if it's just
background music, it changes the mood. It gives your brain
a little bit something else to hook onto and reframe
the information you're getting. So just imagine if right now
you guys were listening to us and we were just
piping through some cabbage or or freshly baked bread, and

(21:53):
how that might change the way that you're considering the information. Yeah,
or even even more than that. It's like, and when
I think of out our, our our use of music,
if we're listening to music, whe we're listening to a
complete composition with various notes to kind of take us
on a sonic journey. So I can easily imagine a
time when you plug in I guess your nostril plugs

(22:14):
or whatever. And uh, and instead of printing with just
a single smell, without it, without it just being a
matter of bread or cinnabon or a certain flower, you
go on a smell journey, say through a garden or
through the French countryside or a spice market and Marrakesh
or something of that nature. Like it. Once the technology
is there and more available, like I feel like we'll

(22:37):
sort of discover its uses more so than we can
sort of predict them. Yeah. Indeed, a scratch and sniff
podcast in right, and already there is some use of smells.
Um and I'm talking in particular with these scent artists
Setel tol Us who used sense as a study aid

(22:58):
for students, which I other we brilliant because we already
know that when you're trying to learn information that your
brain is tagging things in its mind like a map, right,
because it's very spatial, and layer upon that some some
smells and you can really get the thumb tacks in
a little bit deeper. I think, Yeah, she's she's wonderful.
She's the the artist that we we both caught it
the World Science Festival whild Back if I remember correctly. Um,

(23:22):
and it's big into like don't call it stinky, like
like like with children starting early, and trying to frame
our our linguistic understanding of of of scent in a
more nuanced way, like more than just the smell is
good and the smells bad, Like what does it actually
smell like? Well? And she's really challenging people with smells

(23:43):
and what it means to them and what sort of
framework it's it's creating for existence. Um. We've mentioned her
before with the m I T exhibit that she had
a wall painted with the sweat of fearful men. You
would go and smell that wall and smell the fear.
And then there was another one that she did. It
was with donated coats and she did the smell profile,

(24:05):
and I believe that one of them contained, like Chanelle
number five, dog crap and soy sauce. Yeah, I mainly
remember the dog crap. I think was just that her
findings where there's a certain amount of of poop smell
to a certain number of coats, well, and I love
that it's contrasted with the Chanel number five. You know,
it's a fancy lady, and yet she could not escape

(24:27):
the fine patina a feeces covering us in the world. Indeed,
you gotta scoop it up. That's the that's the law,
all right. Well, there you have it, smell, how it works,
how ancient it is, and when, indeed, what the future
of smell might consist of. Now, if you check out
the landing page for this episode on stuff to Blow

(24:48):
your Mind dot com, you'll also find links to previous
episodes we've done that have dealt with with scent as
well as other primary human senses. You'll also find all
sorts of videos, blog posts, linkside to our social media
accoun all sorts of good stuff at stuff to blow
your Mind dot com the mothership of this podcast, and
I bet you have thoughts um Specifically, we'd love to

(25:09):
know about whether or not you would be open to
having a scratch and sniff podcasts, or really any sort
of media that would deliver some sort of pungent odor
to your nostrils. You can let us know your thoughts
by emailing us that blow the mind at how stuff
works dot com for more on this and thousands of
other topics. Is it how stuff works dot com