Last night’s Neuroscience and Society series event was a feast for the senses and the mind, from hearing stories of training noses and palates to trying to train or at least understand our own.
The session, “How Your Brain Distinguishes Tastes and Aromas,” started with a quick science primer by Gary Beauchamp, director and president of Monell Chemical Senses Center. In broad strokes, our conscious taste perception involves the tongue, palate, and part of the throat, while odor perception has two paths: sniffing (orthonasal) or swallowing food, which drives the smell upward to olfactory sensors in the nasal cavity (retronasal).
“People come in [to the clinic] and say they’ve lost the sense of taste, but almost always they’ve lost their sense of smell,” he says. He cited one of my favorite school experiments: tasting jelly beans while holding your nose (see below). While the loss of vision and hearing is damaging to daily life, our very survival depends on the chemical senses, Beauchamp argues, because these are the sensors that tell us we’re eating or smelling potential poisons.
How attuned are we to potential poisons? We have far more receptors for bitter tastes than for sweet or salty, sour or umami—25 different receptors, Beauchamp said. “Nature is mostly bitter,” he said, so to find good things to eat, “we have selected the bitter away.”
Still, there are huge individual differences in these senses. Not one person in the room (of more than 200 people) has the same olfactory sense, Beauchamp said; some are more alike than others but all differ. One example is how we perceive the compounds phenylthiocarbamide (PTC) or propylthiouracil (PROP): Some people find the taste very bitter; other people do not taste anything at all. These compounds can be found in vegetables like watercress, collards, broccoli, kale, and turnips (more on this below, too). “There’s a genetic basis for the ability to detect this particular bitter compound,” he said. In some areas of the world, most people are tasters; in others areas, most are non-tasters. No one knows why; one possibility is there is some other compound the ‘non-tasters’ can taste, sensing some other possible danger, that we don’t know about.
After we got the basics down, we heard from three experts in the practical application of the senses: Kathryn Morgan, a master sommelier, Joan Marrinan, a fragrance evaluator, and Susan Watterson, chef and founder of CulinAerie, a Washington, DC, culinary school. All three described the years of practice it took to be able to identify smells and sensations, and to describe them so another could sense it, too. Morgan said it’s the training that makes the sommelier: “If you like wine, that means your palate is good enough to be a sommelier,” she said, and she has trained many others to do what she does.
Morgan and Marrinan continue to do targeted training—Morgan doing blind tastings of wine and Marrinan studying synthetic smells. “I’m constantly smelling new things,” Marrinan said. While her early training focused on smelling natural oils, “now synthetics play a huge role,” because they can be less irritating. In addition, “There’s all these new fruits that are becoming mainstream” that can be added to a scent repertoire. Perfume evaluators guide perfumers (who are chemists) in the creation a fragrance for the marketplace. Finding the right words to elicit the right scent is key: Marrinan is “the person who explains to the perfumer what the client is asking for,” because she has that vocabulary, she said.
To become a great cook, Watterson said, “You train your palate just by exposure, exposure, exposure.” Her practice is her work: Every time she makes something, the ingredients (especially fruits and vegetables) taste a little different. She must identify the difference and then add something (honey, a certain spice) to make the final dish taste the way the diners remembered it from last time. But it’s not all tasting; “I tell my students they have to develop taste buds in their heads” to predict how ingredients will combine.
“Most people don’t have words for smells,” Beauchamp said. For everything, we say, “it smells like'” something else. Marrinan agreed: “We don’t say ‘I smelled an amazing smell yesterday,'” although perhaps someday we might learn to. What really sells the fragrance, a wine, even a dish, is the way it is described, Marrinan said, so it’s an advantage for a fragrance evaluator, sommelier, or chef, to have a vocabulary that connects with non-experts. Many of our preferences are set in childhood, when we certainly don’t have many words for them.
What will children most likely say is their favorite scent? Crayons, Marrinan said.
“There are wines that smell like crayons, too,” said Morgan.
The audience got their chance to ask questions, and had some great ones. One asked about critical windows for taste preferences: “I believe there’s a critical period, yes, but I also know that we are omnivorous, so we have to be able to learn new things later on,” Beauchamp said. He thinks it’s around the first few months of life, citing work that compounds in breast milk can influence babies’ preferences. That includes residue from smoking: Milk from mothers who smoke smells like “really well-used ashtrays” and studies suggest their kids are more likely to be smokers when they grow up.
Another asked whether it’s really worth it to buy the fancy, expensive vanilla or whether the store brand would work just as well. Yes, but it depends on the dish, Watterson said: If vanilla is the signature flavor, like in sugar cookies, spend the dough and get the good stuff; if it’s not, like in chocolate-chip cookies, you can get by with a lesser brand.
After the talks, we in the full-to-overflowing crowd got to do some personal experimentation. The caterers had set up four tasting stations, corresponding to sweet, sour, salty, and bitter. All worked for this palate.
In a side room, Marrinan set up two smelling stations, with scents on cotton balls under wine glasses. Lifting the glass to my nose, I could sense coffee in one, and pine under another. I wasn’t as good at distinguishing the fruit-based scents beyond “fruity.”
Beauchamp also had a table set up, including the familiar jelly-bean taste test. I held my nose and popped one in: Maybe fruit, maybe watermelon, I thought. Then I let go of my nose—and got a strong sense of strawberry. Funny that we associate taste with our mouths when such a big component is high in our noses.
The best part for me was another item on Beauchamp’s table: white strips of paper containing a bit of the PTC/PROP bitter taste. Turns out I am one of the “supertasters” of that flavor, it was amazingly strong to me, while my husband (here to take the photos) did not taste anything at all on the strip. Next time he is about to “overdose” a dish with broccoli, I’m going to remind him that a little can be a lot.
The session was part of the Neuroscience and Society series, a partnership between the Dana Foundation and AAAS. Video of the panel is up on YouTube. Previous sessions are available via video, including Sleep, The Arts and the Brain, Neuroenhancement, and The Adolescent Brain. Upcoming sessions: Sept. 18 (Stress), Oct. 28 (Illusion).