JULIE MENNELLA, A BIOLOGIST who studies the sense of taste in babies and toddlers, often records her experiments on video. When I visited her recently at the Monell Chemical Senses Center in Philadelphia, she showed me a video of a baby in a high chair being fed something sweet by her mother. Almost as soon as the spoon is in the baby’s mouth, her face lights up ecstatically, and her lips pucker as if to suck. Then Mennella showed me another video, of a different baby being given his first taste of broccoli, which, like many green vegetables, has a mildly bitter taste. The baby grimaces, gags, and shudders. He pounds the tray of his high chair. He makes the sign language gesture for “stop.”
Human breast milk contains lactose, a sugar. “What we know about babies is that they’re born preferring sweet,” Mennella said. “It’s only been a couple of centuries since the time when, if you didn’t breast-feed from your mother or a wet nurse, your chance of survival was close to zero.” The aversion to bitter foods is inborn too, she said, and it also has survival value: It helps us avoid ingesting toxins that plants evolved to keep from being eaten—including by us.
ALTHOUGH THE TONGUE MAP doesn’t exist, there may be a taste map in the brain. A region called the gustatory cortex has been reported to contain clusters of neurons that are specialized to respond to individual basic tastes. Signals from the tongue reach them after passing through the brain stem, and in the gustatory cortex, or maybe along the way, they become part of a complex and only partially understood experience that we commonly call taste but should really call flavor. Linda Bartoshuk told me that only a small part of our experience of food comes from our taste buds. The rest is really the result of a kind of backward smelling.
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