Neurogastronomy: How the Brain Creates Flavor and Why It Matters
by Gordon M. Shepherd
Columbia University Press, 267 pp., $24.95
The worlds we see, hear, feel, smell, and taste exist independently, but we know them only through the fabrications of our brains. The colors we see do not exist apart from our perception of them. The words and sentences we believe we are hearing are a jumble of sounds, whistles, grunts, and silences. From a variety of external signals our brains create something that is not there. In doing so, they help us understand and manipulate our environments. Our sensory worlds—vision, hearing, and touch—are created by combinations of physical characteristics in our environments that stimulate our eyes and ears and skin surfaces. These combinations simplify and stabilize our sensory worlds.
Wavelengths of light or varying pressures of sound waves have very definite physical characteristics that can be measured. We know that our retinas are sensitive to different wavelengths of light and that the spiral-shaped parts of the inner ear, called cochleas, are sensitive to different frequencies of sound.
Gordon Shepherd’s stimulating and informative new book, Neurogastronomy, describes how the brain creates our sensations of smell and taste. Unlike our other sensory experiences—seeing, hearing, touching—the sensory receptors responsible for the brain’s creation of smells and tastes do not react to specific forms, such as the objects and paintings that stimulate our visual system or the waves of sound that stimulate our auditory receptors.
Our sense of touch, for instance, relies on input from nerve cells located in the skin that sense everything from pain to temperature. Yet the process of flavor perception is multisensory and interactive. As Shepherd explains, “A common misconception is that the foods contain the flavors. Foods do contain the flavor molecules, but the flavors of those molecules are actually created by our brains.” Analogizing a flavorful food’s flavor to a colorful object’s color, he goes on:
Color arises as differences in wavelengths of light given off by an object; our brains transform those wavelengths into color to give it meaning for our behavior. Similarly, the smells that dominate the sense of flavor arise as differences between molecules; our brains represent those differences as patterns and combine them with tastes [from the mouth] and other senses to create smells and flavors that have meaning for our perceptions of food.
How then does the brain make sense of the molecules in the foods we eat, or of different kinds of molecules randomly floating on the surface of the wine in a wine glass? How does the brain invent the tastes and odors of Bordeaux wines and Chanel perfume? How does it make combinations of chemicals into smell and taste?
First, the taste receptors on the tongue respond to a broad range of molecules, neatly categorizing them into five types: sweet, salty, sour, bitter, and umami (from the Japanese—a savory or meaty taste). The distinctive balance of these five characteristics makes up the “taste …