NATALIE ANGIER ESSAY

We’ve all heard about the mysterious powers of smell and its importance in love, friendship and food. At the International Symposium on Olfaction and Taste held in San Francisco late last month, Rachel Herz of Brown University and other researchers discussed the many ways our sense of smell stands alone. Olfaction is an ancient sense, the key by which our earliest forebears learned to approach or slink away. Yet the right aroma can evoke vivid, whole body sensations .
In one way, said Jay A. Gottfried of Northwestern University, olfaction is our slow sense, for it depends on messages carried not at the speed of light or of sound, but at the far statelier pace of a bypassing breeze that is enriched with the sort of small, volatile molecules that our nasal-based odor receptors can read.
Yet olfaction is our quickest sense. Whereas new signals detected by our eyes and our ears must first be assimilated by a structural way station called the thalamus before reaching the brain’s interpretive regions, odiferous messages move along dedicated pathways straight from the nose and right into the brain’s olfactory cortex, for instant processing.
Importantly, the olfactory cortex is embedded within the brain’s limbic system and amygdala, where emotions are born and emotional memories stored. That’s why smells, feelings and memories become so intimately entangled, and why the simple act of washing dishes recently made Dr. Herz’s cousin cry.
“The smell of the dish soap reminded her of her grandmother, said Dr. Herz, author of “The Scent of Desire.
Many mammals are clearly nosier than we. Consider that our olfactory epithelium, the yellowish mass of mucous membrane located some seven centimeters up from our nostrils, holds about 20 million smell receptors designed to detect odor molecules delivered either frontally, when we, say, sniff a rose, or via the rear, the volatile aromas that come up through the back of the mouth . The nasal membranes of a bloodhound, by contrast, sustain an olfactory army 220 million receptors strong.
Yet humans can become better nosehounds with startling ease. In one experiment, Dr. Gottfried said, subjects exposed to a single floral scent for just three and a half minutes markedly improved their ability to discriminate among whole families of flower odors. In another, participants soon learned to distinguish normally undetectable differences between one herbal smell and its mirror-image molecular twin if they were given mild electric shocks every time they guessed wrong.
In another presentation, Maria Larsson, an associate professor of psychology at Stockholm University, described the power of smell to serve as an almost magical time machine, with potential for treating dementia, depression and the grim fog of age.
Johan Willander and others in her lab have sought to give firm empirical foundation to the old Proustian hypothesis, the idea that smells and aromas can help disinter the past.
Studying groups of Swedes whose average age was 75, the researchers offered three different sets of the same 20 memory cues - the cue as a word, as a picture and as a smell. The scientists found that while the word and visual cues elicited associations largely from subjects’ adolescence and young adulthood, the smell cues evoked thoughts of early childhood .
Dr. Larsson said people described them in exceptionally rich and emotional terms, and they were much likelier to report the sudden sensation of being brought back in time. They smelled cardamom, and there they were in the kitchen, helping Mama and Nana roll out the holiday buns. The scent of tar, and they’re back at the dock with Dad, tarring the bottom of the family boat .
Dr. Larsson attributes the youthfulness of smell memories to the fact that our olfaction is the first of our senses to mature . The cortical link between olfaction and emotion ensures that those early sensations keep their bloom all life long.