JOHN DANKOSKY: For many people, this time of year is marked as much by festive fragrances as by colorful lights or family meals. That pine garland, those cinnamon cookies, or maybe your nose lights up at gingerbread, wood smoke, or mulled wine. I know every year. I can’t wait for the first whiff of my wife’s Black Forest biscotti. It takes me back to this kind of feeling of nostalgia and comfort. Now, back with us to talk about the staying power of smells and memories and how we can recreate our favorite scent memories at home, it’s science educator, Jennifer Powers, from the Oregon Museum of Science and Industry in Portland, Oregon. Welcome back to the show, Jennifer.

JENNIFER POWERS: Thank you so much.

JOHN DANKOSKY: Explain for us, if you will, this connection between scent and memory.

JENNIFER POWERS: You’re so right because if we touch something, we don’t kind of have that same emotional or memory reaction than we have if we smell it, right? So that’s because the way the signals travel to our brain is different. When we touch something those signals travel directly to the thalamus and that’s responsible for sensory and motor signals. But when we smell something, that signal is carried through the amygdala, and the amygdala in our brain processes emotions, and then it also passes through the hippocampus, which is where we form memories in our brain. And so when we smell something that maybe we don’t smell every day, those special cookies, or that special pie, you can be just hit with overwhelming emotion and memory.

JOHN DANKOSKY: What is a smell made of? What’s entering my nose when I smell something?

JENNIFER POWERS: You mentioned two of kind of the most recognizable holiday smells, right? Cinnamon and then coniferous trees like pine or firs. Both of those kind of signature smells come from chemical compounds. For cinnamon, it’s something called cinnamaldehyde, and for pine trees and fir trees, it’s a group of compounds called terpenes. These substances easily release molecules as gases into the air. And so they’re releasing these molecules and the molecules are floating around us. And that allows our nose, our olfactory receptors to trap them and then send those smell signals to the brain.

JOHN DANKOSKY: You brought us an activity that we can try at home with kids or adults, for really capturing some of these favorite seasonal smells. So how do we do it?

JENNIFER POWERS: This is a really fun family activity, definitely great for adults to be around because it does require a stovetop and some hot utensils.

JOHN DANKOSKY: Fair enough.

JENNIFER POWERS: But you’re going to want to start with a pretty large pot on your stove and heat up a couple cups of water, and you’re going to want to place an empty glass jar in the water, start heating it up, and then the fun part is you get to pick out something that smells good, pine needles, for example, throw a bunch of pine needles into the water. And then you’re going to cover the pot with an upside-down lid. And then you’re going to place ice cubes on the top of that lid and you’re going to let everything simmer for about 10 minutes.

And what’s happening is as those items, those pine needles are heating up in the water, they’re releasing all of those really super smelly molecules into the air and the gas and the steam is inside your pot but then the ice, it hits the ice which is cooling it down causing all that water vapor and all those smelly molecules to condense back into a liquid that eventually falls into your empty jar in the center of the pot. So after about 10 minutes you can carefully remove the lid, use tongs, very important, to take the very warm jar out of the pot, and then you’ll find that the liquid you captured smells like the smelly stuff you put inside the pot. And it’s just so fun and so cool.

You could also keep experimenting with it, right? If you want to capture pine scent in one jar, maybe cinnamon in the next, you could combine them together to make a super smell. You could even make a mystery smell. You could put something in there and try to fool your friends and family, see if they can guess what it is.

JOHN DANKOSKY: I love this. Well, we’re out of time but for more on the connection of scent and memory and how to capture these memorable scents at home you can visit our web page, it’s sciencefriday.com/smells. Thanks so much for joining us once again, Jennifer.

JENNIFER POWERS: Of course. Thanks for having me.

JOHN DANKOSKY: Jennifer Powers is a science educator at the Oregon Museum of Science and Industry in Portland.

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