How Smell Guides Our Inner World

Summary

When Thomas Hummel gets a whiff of an unripe, green tomato, he finds himself in his childhood home in Bavaria. Under the tilted ceilings of the bedroom that he shared with his two older brothers, there were three beds, a simple table and a cupboard. “My mother put those green tomatoes on the cupboard for them to ripen,” said Hummel, an olfaction researcher at the Carl Gustav Carus University Hospital in Germany. “They have this very specific smell.” It’s grassy, green, pungent, rough and bitter, he said. When he passes by a bin of tomatoes at the market today, “it is always to some degree emotional,” he said, “like every smell is emotional.” Smell is deeply tied with the emotion and memory centers of our brain. Lavender perfume might evoke memories of a close friend. A waft of cheap vodka, a relic of college days, might make you grimace. The smell of a certain laundry detergent, the same one your grandparents used, might bring tears to your eyes. The Quanta Podcast How do scent molecules translate into a neural language that triggers emotions and memories? All episodes Your browser does not support the audio element. Smell is also our most ancient sense, tracing back billions of years to the first chemical-sensing cells. But scientists know little about it compared to other senses — vision and hearing in particular. That’s in part because smell has not been deemed critical to our survival; humans have been wrongly considered “bad smellers” for more than a century. It’s also not easy to study. “It’s a highly dimensional sense,” said Valentina Parma, an olfactory researcher at the Monell Chemical Senses Center in Philadelphia. “We don’t know exactly how chemicals translate to perception.” But scientists are making progress toward systematically characterizing and quantifying what it means to smell by breaking the process down to its most fundamental elements — from the odor molecules that enter your nose to the individual neurons that process them in the brain. Severa...