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Steven Munger loves the sour smell of a butane lighter. The hydrocarbon, butane, is colorless and odorless, but sulfurous additives give it a stench that’s almost objectively foul. Almost. To Munger, a neuroscientist who studies our chemical senses, the aroma conjures memories of his grandfather’s lighters. He remembers playing with lighters, flipping them open and lighting them. “The smell was everywhere,” Munger says.
Smells can create lasting memories and can be used to trigger deeply buried memories. “A fish smell might be unappealing,” Munger says. But if you grew up spending time on boats around family members who fish, you might respond more positively. The same chemical smell can elicit different meanings for different people, and in different contexts.
Unlike sight, sound, and touch, the smells and tastes we sense are all chemicals. The associations we peg to chemicals have long captivated Munger. He first studied chemical sensing in crustaceans as a college student before moving on to lab mammals such as mice. He is now a professor at the University of Virginia in Charlottesville, Virginia, studying the mysteries of our chemical senses.
In this interview, Munger discusses his round-about journey into chemistry and the mysteries of smell and taste that have kept him fascinated throughout his career.
—Max G. Levy
STEVEN MUNGER
EDUCATION:
B.S.: Biology, University of Virginia
Ph.D.: University of Florida
WHAT HE DOES NOW:
Professor and Co-Director of Research, Otolaryngology at University of Virginia
This interview was edited for length and clarity.
Did you always expect to study chemical senses or chemistry in general?
I was not a great chemistry student. It didn’t really click for me. I ended up approaching it from the biological side.
How did biology lure you into chemistry?
By pure chance. When I was an undergraduate, I was interested in neuroscience and marine biology and looking to work in a lab. One professor had been working on the reflex of mantis shrimp, which can [punch] the water and stun its prey. Well, they weren’t working on that project anymore, but they were studying the sense of smell in crayfish.
I just became really fascinated with sensory biology in general—how we understand the world around us.
What fascinated you about the chemical senses?
With smell and taste you get this complexity where your nervous system has to tease apart different chemicals and then put them back together in some way.
What do you mean?
Taste is simpler. There are dedicated receptor proteins in taste buds tuned to recognize different types of chemicals. The way they’re wired into the brain dictates what detecting those chemicals mean. There’s a receptor that recognizes sugars and chemicals we know as sweeteners. There’s another group of receptors that recognize alkaloids and other chemicals for bitterness. Then there’s salt, and sour, and umami. And that’s about it.
There’s also an innate “hedonic valence.” Basically: Do you like it or not? If you give sugar to a baby, they will smack their lips and smile if they’re old enough. It’s innately appetizing and pleasant. If you give the baby a pure bitter compound, they will grimace and stick their tongue out and try to get it out of their mouth. It is innately aversive, and that’s because a lot of bitter-tasting compounds are poisonous.
How is smell more complicated?
For the most part, smell is about learning. There are cells with specialized receptors in your nose—we have about 400 different odorant receptor genes—but sensing is more about pattern recognition. If you get the aroma of pizza, which has a bunch of different chemicals, our best understanding is that they’re activating receptors to different degrees. That elicits a pattern that your brain had previously learned to associate with pizza, because when you first smelled it, you were sitting in front of a pizza.
So, in smell chemistry, a handful of receptors combine for an almost infinite number of patterns?
Exactly. The term that we use is “combinatorial coding.” Also, chemicals might activate the same receptor but do so to different degrees. And we don’t understand all of it, because
we only look in certain parts of the brain well enough to see those patterns.
Given that the brain wiring of smell is so complicated, how do you study it?
We tend to work with “monomolecular” odor-ants. Single chemicals like isoamyl acetate, which you would recognize if you’ve ever smelled banana candy. Another is R-(-)- and S-(+)-carvone. They are chemically identical enantiomers, or left-handed or right-handed mirrors of each other, but one smells like spearmint and the other smells like caraway seeds.



How do our chemical senses affect the rest of the body?
There’s a question about how much interplay there is in taste recognition of nutrients and your body preparing to metabolize those nutrients. How much do your nutritional needs feed back to the taste system to affect your dietary choices?
Do you have advice for students for whom chemistry may not be clicking?
It's not something to be afraid of. Chemistry is something to define your relationship with. We are bags of chemicals, and everything we're interacting with involves chemistry.