We Have the Technology Page 3
This won’t be a trivial choice. We are a species on the cusp of tinkering with its own evolution, of driving technology deeper into the flesh, away from the periphery and toward the seat of perception. We are learning to interpret the brain’s language, the data flow that turns electrochemical fizz into sensations, experiences, feelings—the very stuff of being. And if we can understand this information, we can modify it. To borrow once again from the analogue world of print: As any hack knows, it is powerful to read and write. But it is more powerful still to control the edit.
PART ONE
The Five Senses
ONE
Taste
MIKE ARCHER CAREFULLY LAYS OUR SUPPLIES on the lab countertop: A DNA collection kit. A kitchen timer. A bottle of water. A bag of oyster crackers. A green file folder, which he opens to reveal a set of plastic baggies taped neatly inside, each containing a gel wafer the size of a postage stamp. There’s also a mysterious device with puffy foam disks on its pincer ends. These are my nose plugs. Archer mimes how to gently clamp my nostrils shut, so I can taste but not smell.
“I want you to do a little sniff test to make sure you don’t have any air going through your nose,” he says.
I try them on; it’s like instantly having the world’s worst cold.
“Perfect,” Archer says. The experiment is ready to begin.
Behind us, it’s a snowy school day morning at the Denver Museum of Nature & Science. Eddies of jubilant kids on field trips, wearing borrowed lab coats and goggles, blow through the adjacent biology exhibit, where they can extract DNA from wheat germ or measure the sugar in breakfast cereals. Every now and then they glance curiously through the enormous plate glass doors that separate this working lab space from the rest of the museum.
Archer, a retired dentist, is a volunteer, part of a small army of “citizen scientists” who power the Genetics of Taste Lab, the formal name for our setup on the other side of the glass. The lab coat he’s wearing is mostly for show, something that delights the kids, he says. But the test we are about to do is real; if it works, it will shed some light on one of the biggest mysteries in sensory science. We are going to see if I can taste fat.
Not bacon.
Not cream.
Just fat. Or, more specifically, fatty acids. Or, even more specifically, linoleic acid, an omega-6 polyunsaturated fatty acid, which is vital to the human brain and immune system and for that reason is something researchers think our bodies might be able to sense in our food supply. On the wall, which has been painted to look like an enormous lab notebook, there’s a diagram of a linoleic acid molecule, its two arms shaped like a ladder bent to the right. If I—and the 1,500 museum visitors taking part in this experiment—can taste fat, we will have helped prove whether or not there are more than five basic tastes. Or, to put it more bluntly, we will have helped show whether there are still unnamed, unexplored dimensions to a sense we thought we already knew.
The five basic, or primary, tastes are listed on an easel propped up on the lab counter: salty, sweet, sour, bitter, and umami, which is sometimes described as savory. These are considered the building blocks of taste, essential parts which cannot be further subdivided, just as red or blue cannot be fragmented on the color wheel. Chemicals in food bind to receptors that are embedded in bulb-like clusters of cells that are called taste buds, and this information travels along the gustatory nerves to the brain, where it is ultimately interpreted. Some of you may remember a time when there were only four basic tastes; umami didn’t officially make the list until 2000, although the concept had already existed for a century in Japan. It was discovered in 1908 by Dr. Kikunae Ikeda, who argued it was a fifth taste associated with the amino acid glutamate. Its acceptance upended the food research world, hinting that the taste universe was bigger than previously thought, casting doubt on the definition of a basic taste itself, and fueling a quest to see if there are more primaries. Much like seventeenth-century astronomers who suspected there were planets beyond the orbit of Jupiter, scientists are now searching for new candidates that would enlarge our known system.
Fat, championed by nutrition scientist Dr. Richard Mattes at Purdue University, is one of the leading contenders. “We think that fatty acids generate a unique sensation,” he says, something separate from the other five.
While the taste research community has no formal list of what qualities are required for basic tastes, Mattes has come up with six well-respected rules of thumb. Among them: There must be receptors for the taste stimulus on the tongue. (Two fatty acid receptors, CD36 and GPR120, have been localized to taste cells, and Mattes expects others might be found, too.) That information must travel to the brain along the gustatory nerves rather than the trigeminal nerve, which conveys information about touch—information that in the case of eating is called “mouthfeel.” This last requirement is particularly confounding when it comes to fat, which is clearly also a mouthfeel and indeed a reason why creamy, fatty foods are so appealing. “That’s one of the big issues—is it really taste or is it just texture?” Mattes says. “Differentiating those is very, very, very, very, very tricky, because to taste something you have to have it physically in contact with your tongue.”
In human studies, researchers often try to separate taste and texture by administering the fats as liquids, with mineral oil added to mask lubricity and gums to mask viscosity. Nose plugs are used to block odor, and some testers use blindfolds or red lights to eliminate visual and coloration cues. With rodents, people have tried cutting the gustatory nerves, and found that the animals became less sensitive to fatty acids, suggesting the information is carried on that nerve, not just the trigeminal one, Mattes says.
According to Mattes’ guidelines, a basic taste must also serve a biological purpose. Most taste researchers believe the primaries fall into one of two broad camps: attractive and aversive. They generally agree that we are attracted to sweet taste, which signals where the carbohydrate energy is, and umami, which signals the presence of protein, specifically, amino acids. We avoid bitter, which often indicates the presence of toxins. With saltiness, which signals the presence of essential electrolytes, and sourness, which indicates acids like vitamin C, researchers don’t always agree, but some think it’s probably a matter of concentration and satiety. We eat a little of the foods containing these chemicals when we need them, but they may become aversive at extreme concentrations or when we’ve had enough. (Mattes points out that people eat all of these things, sometimes simply for pleasure, and that any of them can become repellent if you’ve had too much.)
A basic taste also prompts a physiological response. Fat usually comes in the form of triglycerides, which contain fatty acids. While free fatty acids are found in some foods, in other cases when their concentration is too low for detection, the body must produce a salivary enzyme called lipase, which chips the fatty acids off the triglyceride. “Mice have plenty of it, and it’s been shown very clearly that when you block the activity of this enzyme they don’t detect and prefer fat,” says Mattes. But there are questions about whether humans produce enough lipase to break down triglycerides, producing enough of these acids to let us taste fat. Mattes has shown that chewing fatty foods like coconut and almonds prompts the release of lipase—enough lipase, he thinks, for us to taste fat. So there’s a possible physiological response: Chew the fat, produce more enzymes. (One related hypothesis, says Mattes, is that hard fats like coconut prompt a bigger response than soft ones like olive oil: The harder you chew, the more you salivate, the higher the lipase concentration.)
But the ne plus ultra is whether anyone can actually sense the taste, and whether that sensation is distinct from the five we already know. That’s where the museum comes in, with its constant influx of visitors of all genetic backgrounds, many of them arriving in family groups (always a boon for genetics researchers). Like me, each participant will swab the inside of their cheek with a giant Q-tip and hand it over for testing. Like me, they’ll learn to “swish an
d swallow” from the water bottle to cleanse the palate between tests, and be directed to make use of the oyster crackers in case they encounter a taste that is exceedingly repellent. And then they’ll try some fatty acids.
Archer opens the file folder and extracts the first of the wafers. It’s a gelatin square the color of onion skin, and perhaps a bit thicker. If you’ve ever used a meltaway breath strip, you’ve seen this technology before. But instead of minty freshness, each strip is infused with a different concentration of linoleic acid.
Archer explains how to do what’s called a scaling test. I’ll place each strip as far back as I can on my tongue, holding it there for 45 seconds. We’ll do three practice strips, and then four more to test whether I can perceive the linoleic acid at different strengths. After each exposure, I’ll rate the strength of the sensation. The concentration of each strip will vary, perhaps including placebos with no fat at all. “This is a double-blind study, meaning you don’t know what these are and I don’t know what these are,” Archer says, gesturing toward the file.
All right, nose clips on? “Nose clips on,” he says.
The first two practice rounds are easy. One strip, Archer tells me straight out, has no taste—it’s just to get me used to the feel of the wafer. It’s gummy, and holding it carefully on the tongue while resisting the urge to bite through it conjures some distinctly Communion-related memories. Another strip is laced with one of the five known basic tastes; my job is to identify which. (I guess sweet.) The third round is harder. This wafer has linoleic acid in it; this is the only time in the study I’ll know for sure that there’s fat to be tasted. The point of this round is to clue my taste buds in to what they’re searching for once we launch the true tests. It’ll also be my first hint about whether there’s something to this fat idea, or whether I’ve joined a gustatory wild-goose chase.
Archer proffers the gel strip and readies the timer. “Close your eyes. Just kind of concentrate on what you’re experiencing, OK?”
At first, there is nothing. Maybe 15 seconds of gelatinous blandness. And then there is a wash of … something. My mouth puckers. The first word that springs to mind is bitter.
But that’s already a basic taste. Try again.
Acid, my brain suggests.
But acid is essentially sour, another basic taste.
My mind flails. How am I ever going to describe a possible sixth sensation without using the terminology of the other five?
And here I have run into the secret second purpose of the museum experiment. We’re not just here to see if we can taste fat. We’re here to see if we can describe how fat tastes. Searching for the sixth taste, it turns out, isn’t only a technical problem; it’s a word problem.
The lexical challenge hinges on this: How can you perceive something if you don’t have a word—and therefore an established concept—for it? In order to recognize a new basic taste, we’ll have to train ourselves to discern a separate, distinct quality among the foods we have been eating all along. Taste researchers often compare this conundrum to the idea of isolating a new color. The rainbow’s not going to grow, but we might find a new way of categorizing its light, of seeing a particular bandwidth as a discrete, unique entity. There’s linguistic precedent for this kind of sensory category sorting: researchers point out that not all cultures break down the light spectrum the same way. Some languages don’t have separate words for green and blue, for example. That doesn’t mean people who speak those languages can’t see both colors. It means that they perceive them as a singular experience, while people raised with a language that distinguishes between them perceive them as separate. And as the German philologist Lazarus Geiger determined in the nineteenth century by studying ancient texts, early cultures tended to develop words for colors in a similar order: black and white first, then red, yellow, green, and finally blue. While at the time he wondered if this might be the result of anatomical evolution, today it can be read as either a linguistic or conceptual change—depending on which side of the debate you’re on. And so it may be with taste. Maybe fat’s been in the taste rainbow all along; we just don’t have the vernacular to call it out.
“It’s a total language problem,” says Dr. Nicole Garneau, the museum’s curator of human health, shaking her head knowingly. “And we stumbled upon that right away.” Garneau is an energetic young geneticist with bright blue eyes and a rapid-fire way of speaking who came to the museum after an early career studying yeasts and viruses. The museum wanted to teach genetic concepts in a personalized way, one that would allow visitors to learn about their own bodies and participate in ongoing scientific work. The team focused on taste because the related genes are so individually variable, and zeroed in on the question of a sixth taste because they thought it would excite visitors more than donating their DNA to the umpteenth study on, say, bitter perception. “We wanted to ask questions and do research that is potentially high risk and high reward, because that’s what the public is interested in,” says Garneau. “They want to be at the cutting edge.”
But just putting out a press release advertising the study forced the museum staff to confront the language problem: What were they going to call this phenomenon? Their solution, for marketing purposes at least, was “fatty acid taste,” a phrase that is precise, if not exactly satisfying. The problem, Garneau points out, is that “fat taste” doesn’t evoke a particular mental image. We have no percept for what fat should taste like, and no descriptive language for it. Our descriptors were built for the first five tastes, and we tend to stick to them even though they are frustratingly limited. “If I give you black coffee and I say, ‘Describe this, but don’t use the word “bitter,”’ or I give you sugar and say, ‘Describe this, but don’t use the word “sweet,”’ it’s very difficult to do,” Garneau says. “So that’s the pickle we’re in right now.”
The museum’s way around this mental roadblock is crowdsourcing. Maybe after free-associating their reactions, the 1,500 participants will collectively describe this thing in a way that will let their fellow humans recognize it. “That’s 1,500 brains that are a lot smarter than just one scientist, who is going to use some science-y name that isn’t going to be relevant,” says Garneau. “We’re going to have something simple, that is relatable, that the community can embrace and say, ‘That’s the sixth taste, and I understand what it means.’ ”
Archer clicks the kitchen timer. Time to come up with some relatable words. Archer warns me not to evaluate how pleasant the taste is. “I am not interested in good, bad, or gross,” he says. “That doesn’t tell me anything.”
So I say the only word I’ve got that isn’t already a basic taste: varnish.
Archer nods, pushing a paper toward me. Cleaner, I write. Solvent. Not too astringent. Not like, say, Pine Sol. Mellower. Funkier.
Next, Archer has me take off the nose clips. The experience most people call taste is more accurately known as flavor, the combined work of the mouth and the nose. When we eat, scent molecules travel from the mouth up the nasal cavity, and the brain processes them in combination. (The scientific term is “retronasal olfaction.”) Flavor perception can be dramatically altered by odor, and so the museum wants to test this, too. “Let’s take off the clip before you lose that entire thing. What do you think it smells like?” he asks.
The scent is already vanishing, as ephemeral as dream logic. “Just the faintest whiff of shoe polish,” I finally say.
Now it’s time for the scaling tests. My task is to determine if I can sense that taste again and rate its strength by drawing a mark on a scale line. The next four gel wafers will each contain a different concentration of linoleic acid; I place each in turn on my tongue as Archer mans the stopwatch.
The first tab is weak, the ghost of wood varnish. I mark what would be 1 on a scale of 10.
The second is much stronger, a 7 now, still that lacquer-like tang, although this time when Archer asks me to remove the nose clips, an extra level of funkiness emerges. “There is s
omething old about it,” I say. “Stale air. Or suitcase leather or old luggage.”
And also: Is my mouth watering? If so, is it because it’s almost lunchtime and these wafers are the first food-like objects I’ve put in my mouth all day? Is it the autosuggestion of the writer who read a whole passel of studies about fat taste before coming to taste fat? Am I salivating because people in Mattes’ coconut study did it? Heck, am I salivating because mice do it?
I am sure about one thing: Whatever is happening is not fun. On the third try, I nearly become the first person to break into the emergency oyster crackers. Not only is the taste sharper, but the acid feeling in my mouth has progressed to the pit of my stomach, where that distinctive “too much coffee” digestive drumbeat is starting up. After the longest 45 seconds yet, Archer finally stops the timer. Definitely a 9.
“Ugh,” I manage. “Brlrlrlrhgghghgh.” I try to come up with some more scientifically useful words. Plastic? PVC pipe? Shoes? I’ve defaulted to metaphor. All my adjectives have failed.
Time for the last trial. I keep an eye on the crackers. But this tab is, I am pretty sure, the placebo. I sense nothing, and my contribution to taste science is officially over. I’ll have to wait until 2016 to see how the other 1,499 tasters fared.
For the record, most people don’t do much better. When I ask Mattes if he can describe fat, he flails, too. “No! No, I can’t! It’s awful. Period!” he says. “It sucks the air out of your lungs. It’s just terrible. Nauseating. It’s rancidity. It’s really, really bad cooking oil, the sensation that that gives you.” At first, most people default to a familiar basic taste: bitter. “But we don’t think bitter is actually the word,” says Mattes. “Bitter is just being used as a way of saying it’s awful.”