I love fall.

The colder weather, the changing leaves, the excessive, pumpkin spice, everything.

We all have things that we associate with fall.

For me, it's fresh Apple cider donuts.

So good.

I called them a bunch of friends and asked what does fall mean to you?

I'm Kallie.

My name is Justin I'm Alex.

I live in Brooklyn, New York.

Beautiful Mojave Desert.

Missoula, Montana.

Lafayette, Louisiana.

When I think of fall, I think of home in beautiful leaves on trees.

Do you love fall?

It's the crisp air Crunchy leaves.

Where is Yankee candle, when you need them?

In most places, fall is beautiful.

You get this change of leaves from green to shades of red and orange, but what we often find most striking about the fall are the smells and how those smells make us really happy.

We used to always go Apple picking when I was a kid.

And so I think of the smell of an Apple fresh off a tree.

The smell of Apple is actually tons of different compounds, including butyl acetate, hexyl acetate, and 2-methylbutyl acetate There's pine everywhere.

And that's a very strong, beautiful smell.

A lot of that pine smell comes from alpha pinene.

When you're about to carve a pumpkin, the first crack... it's the freshest pumpkin smell that you can get.

Anything pumpkin-related really is what I think of when I think of fall.

And you can thank CIS-3-HEXENOL and HEXANAL for a lot of that pumpkin smell Pumpkins are great and all, but add some spices turn it into a latte, that is pure fall joy.

A lot of the pumpkin spice smells have nothing to do with actual pumpkin.

And it's actually made up of compounds like cinnamaldehyde and 6-gingerol Whatever don't judge still delicious.

Mmm.

So how do a bunch of molecules just floating around in the air translate to, "oh, I'm smelling pumpkin spice and wow, it's making me so happy."

When you inhale an odor molecule, it binds to receptors on cells in your nose called olfactory sensory neurons.

We each have millions of olfactory sensory neurons, and each of those neurons has just one type of hundreds of possible receptors.

Having a huge number of these neurons and potential receptors means you can identify and distinguish between tons of different odors, which is just so cool.

So when George takes a whiff of that pumpkin spice latte, the cinnamaldehyde and 6-gingerol and other odor and compounds will travel into his nose, bind to their respective receptors, and then electrochemical signals are sent to George's brain that George's brain translates to "Hmm, pumpkin spice."

But there's more to the story than that.

See, when those odor compounds bind, they send a signal, that reaches a bunch of different regions of your brain, including your amygdala and hippocampus, which process emotion and memory.

So you start creating a connection between the odor compounds and the context in which you smelled them.

Once we have an association to a smell and we smell it later, it instantly triggers the association-emotion connection.

And that is to say, it can, we can experience smell in pure smellscape without having any thoughts or higher order cognitive processing going on.

And that feeling is really the most potent and powerful and often distinguishing thing about our sense of smell Our emotional connection to smell makes it really personal.

The first time that George smelled something with pumpkin spice, it was probably a positive experience because he still has these happy memories of it today.

For me, the smell of an Apple orchard is so wonderful.

But again, context, I always had a lot of fun Apple picking.

Someone else might totally despise that smell.

And it's because they never enjoyed Apple picking as a kid.

That psychological aspect of smell helps explain why we get so happy when we smell things that we wouldn't normally consider sparking joy.

This one's maybe a little weird, but I think about the weird plasticky smells around those orange plastic tubs that people keep their candy in.

Death and decay are also responsible for a lot of those happy, false smells.

The first thing that pops into my head is the smell of decaying leaves.

As the leaves start to fall, you can smell them.

There are sections of road around here that have unpicked apples that fall onto the road and then get crushed by the cars.

And it is the sweetest smell of Apple.

When apples and leaves drop to the ground, microbes will come in...

So that's bacteria, yeasts molds, and then they'll start to break them down.

As that's happening, the leaves and the fruits begin releasing odor compounds and the microbes actually start releasing odor compounds as well.

A lot of those odor compounds actually overlap with what you might find in a swamp where there's a lot of plant debris, also being broken down.

Here in Savannah, more likely to smell kind of a swamp.

The desert gives off a smell of compost and mild swamp gas.

Whether or not you like a smell, like the smell of a swamp is totally unique to you.

We actually did a video a few years back on stinky cheeses.

And although some of them are described as smelling a bit like a dirty gym sock, people still like that smell.

So it turns out that how you label a smell provides context that really matters.

One person could smell the exact same smell and interpret it in two different ways and have two totally different reactions.

I took this compound.

That was a combination of isovaleric and butyric acid, which smells, depending upon how you code it, as Parmesan, cheese or vomit.

And, um, depending upon the label that I presented this smell with, people would either say, "I love this smell", or "I hate the smell".

But in the, in that particular vomit/ parmesan cheese connection, it was extremely powerful to the point where people would not even believe that it was the same smell they were smelling on both occasions.

I really hope that the smells you associate with fall are more on the Parmesan cheese, under the spectrum versus the vomit end of the spectrum.

But what about kids right now, during a pandemic?

Where we are most likely to form associations with smell is the first time we smell them and often the first time we smell them is in childhood.

So if you are a little kid right now, and your first Halloween is pandemic Halloween, your smell associations for fall may end up being different than they would be if your first fall Halloween excursion was last year.

So a little kid whose first Halloween or first fall that they remember was in 2020 might forever associate fall with the smell of the inside of a face mask.

It's not a campfire or a plastic bucket for trick or treating, but it still might bring back really happy, fall memories for decades to come.