When we think of a flavor, what comes to mind is usually the distinctive qualities that separate it from other flavors: the singular “coffeeness” of coffee. That is, a mix of tastes, aromas, mouthfeel, and temperature. But that’s really only half the equation. The other is how that coffee makes you feel. You sip it not just to fill your stomach, or even to wake up, but to get a little pleasure and satisfaction. Without that, drinking it would be a very dull experience indeed, a flat collage of sensations. Pleasure is what animates eating and drinking and makes them truly gratifying.
In the brain, the networks of neurons responsible for pleasure overlap with, but operate separately from, those that generate the “coffeeness” sensation. Sometimes these perceptions are so tightly bound together they’re indistinguishable, such as during the first bites of a meal. At this point, the stomach is rumbling, the mind is primed to eat, so pleasure is at its height. But as the belly fills, everything continues to taste more or less the same (if less vivid) while the “mmm” sensation declines, then disappears. Otherwise, we might keep eating till we exploded.
How pleasure works—and indeed, its exact purpose in eating and human behavior—is a hotly disputed topic among scientists. But no scientific question is more important for chefs, food companies, and any people who pride themselves at being handy in the kitchen.
For much of the 20th century, scientists viewed pleasure as a second-class sensation, a kind of afterthought to the real motivators: pain and discomfort. The field of behaviorism, for instance, was founded on something called the theory of “drive reduction”: certain drives (hunger, thirst, sex, et al.) basically forced animals to act to alleviate discomfort. Supposedly, virtually all behavior could be traced to these. Relief and pleasure were behavioral rewards—important, sure, but since they came afterward, secondary.
Only recently has pleasure begun to get its due. It’s turning out to be more complicated than anyone suspected.
Kent Berridge, a neuroscientist at the University of Michigan, began working on the pleasure problem in the 1980s. Scientists at that point thought that dopamine, the powerful neurotransmitter associated with movement and motivation, was the brain’s “pleasure chemical.” But Berridge grew suspicious when, in an experiment, rats that had been given a dopamine suppressant still licked their lips when drinking sugar water—basically, the rodent equivalent of a spontaneous smile. If rats were smiling without dopamine, something else had to be involved. After years of experimentation, Berridge isolated a pleasure circuit in the brains of rodents, which hinged on knots of neurons near the brainstem he dubbed “hedonic hot spots.” When firing, they generate intense pleasure. So far, they have not been isolated in humans, but Berridge postulates they are a feature of mammalian brains.
Read the full article "How food and drink tickle the brain’s pleasure centers" at Slate.