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Smell: the undervalued sense

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January 29, 2012|By Ruth Graham

Gordon Shepherd, professor at Yale School of Medicine and author of Neurogastronomy:…

When the marketing firm McCann Worldgroup surveyed thousands of young people last year about what they value most, more than half of the 16- to 22-year-olds said they would rather give up their sense of smell than their phones or laptops. Researchers presented this as an example of a particularly modern youthful attachment to technology, but it is also a sign of the persistent human disregard for the sense of smell. Plato associated smell with base urges; Aristotle wrote that “man smells poorly.” Kant dismissed both taste and smell as inferior to the other senses.

In fact, however, smelling engages huge regions of the brain — not just memory and emotion, but also our systems for language and higher cognitive processing. Breathing in an odor creates a complex pattern in the brain, comparable to the one we use to recognize faces. In contradiction to Aristotle, we’re not just good at this; our powerful brains make us uniquely skilled. And when it comes to what we eat — both our flavor perception and the decisions we make — the sense of smell is firmly in charge.

That motivated neurobiologist Gordon Shepherd, a smell expert at the Yale School of Medicine, to write a book about the connection between smell, flavor, and the human brain. Shepherd’s own research began in the 1960s, and one of his first major breakthroughs was the discovery of the “odor image,” the raw pattern of a smell that gets passed up to the brain for processing. His new book, “Neurogastronomy: How the Brain Creates Flavor and Why It Matters” (Columbia University Press, 2011), is his first for a general audience, and at the heart of it is an argument that smell is far more important to humans than we recognize.

Grade-school science students learn that smell affects flavor when they perform the pinch test: squeezing their noses closed, putting a bit of candy on their tongues to experience a simple sweetness, and then opening their noses to release a much fuller flavor. What they don’t learn is the true extent of what’s happening when they do that. As Shepherd writes, “retronasal smell,” in which we send little puffs of air out and backward into our nasal passages as we eat, almost instantaneously engages “activity at the highest cognitive levels of our brain.”

Only if we understand that activity better, Shepherd argues, can we truly understand nutrition, obesity, and aging. Smell affects what we crave, what we become addicted to, what we find pleasure in, and even the will to live. He connects declining powers of smell in the elderly to “failure to thrive,” and says that flavor may point to public policy solutions to poor eating habits. Shepherd spoke to Ideas by phone from his home in Connecticut.