Sometimes I’ll be walking down the street on an ordinary day, just minding my own business, when suddenly I’ll catch a whiff of something that brings forth a flood of memories so powerful that it nearly knocks me over. And I’m not talking about exotic scents like the tuberose lei I wore at my wedding; these are run-of-the-mill aromas that can be found in most drugstores and shopping malls. For example, when I washed my hair with Pantene Pro-V at a friend’s house recently, I was instantly transported back to summer camp in 1988, where I took showers in a communal log cabin, snuck out at night, and “fell in love” for the first time.
Another day, when I met a very glamorous woman at an art show in Los Angeles, I was so distracted by the smell of her perfume that I couldn’t even focus on what she was saying, so caught up was I in my recollections of being in my best friend’s room freshman year of college as she got ready to go out for the night—and filled the air with that very same fragrance as she spritzed it on her wrists. I could picture everything about that moment—the shape of the perfume bottle, the clothes my friend was wearing, and even the music that was playing—all because a stranger in an art gallery was wearing the identical scent fifteen years later.
At first I thought I had some kind of supersniffer that conjured up these vivid mental images for me alone, but I’m not the only one after all. On the contrary, of the five human senses, the sense of smell (also known as olfaction) is the strongest trigger of memory for most mammals.
An Olfactory Journey
Approximately one thousand sensors exist in the human nose, and they’re capable of picking up as many as ten thousand different odors. The shape of the molecules that each odor is composed of is unique to that particular aroma. When we inhale, we absorb these molecules into our nasal passages, whereupon they bind to complementary chemoreceptors in the olfactory epithelium, a one-centimeter-square patch of tissue above and behind our nostrils that’s specifically responsible for identifying particular smells. These chemoreceptors then send information about the specific scent to the brain’s limbic system, which reads the signals by comparing them to past experiences the person has had with the same smell or similar smells.
That’s not the limbic system’s only role, though—it also regulates moods and feeling and serves as a sort of storage facility for memory. Therein lies the reason why certain aromas provoke certain recollections so powerfully: as the limbic system receives a particular fragrance that the smeller has experienced previously, it automatically calls forth the memories associated with that experience and thus forges a long-lasting bond between the scent and the story behind it.
Many researchers have been experimenting with constructive practical applications for olfactory memory. In the March 2007 issue of the journal Science, for instance, Björn Rasch, Christian Büchel, Steffen Gais, and Jan Born described the results of a study they conducted about how sleep and familiar odors working concurrently appeared to boost the participants’ memory, at least during the stage of somnolence known as slow-wave sleep. These four scientists asked medical students to play a computerized memory game in which they attempted to create identical pairs of cards by turning the cards over individually, then remembering where they’d seen each card’s match. Some of the students did this exercise in a rose-scented room, while the others did not. Once the former group of participants had reached the slow-wave sleep stage that night, the scientists administered a second dose of rose scent to their nostrils.
When the participants awakened, the researchers asked them all to try to recall the locations of the cards they’d seen in the game the day before. Of the group that had been exposed to the rose scent, 97 percent remembered the cards’ placement correctly, compared with only 86 percent of the students who’d been in the unscented room during the game.
Wake Up and Smell the Rosemary
Proponents of herbal remedies have long believed that rosemary is a brain stimulant that facilitates human memory—in fact, the forsaken character Ophelia even utters the line “There’s rosemary, that’s for remembrance” in William Shakespeare’s Hamlet. The Web site HowStuffWorks.com recommends using the herb as the basis of a recipe for a memory-boosting academic aid. Combine ten drops of rosemary oil, six drops of lemon oil, one drop of clary sage oil, and two ounces distilled water in a spray bottle. Spray the mixture on a cloth and sniff the cloth repeatedly while studying for a test; then take the same cloth to the exam site and inhale the scent while taking the test. Theoretically, as your limbic system processes these now-familiar olfactory signals, the information you studied will return to you with greater clarity.
Though animals generally rely much more heavily on their sense of smell on a day-to-day basis—to recall where they’ve stored food, to detect fear, and to find their mates—than humans do, that doesn’t mean we should underestimate the power of our noses, as they benefit us in ways that we’re not even conscious of sometimes: even a breast-feeding infant can distinguish his mom’s particular scent from that of every other nursing mother. Granted, given that thousands of smells traverse our nasal passages every day, we’re bound to come across a multitude of odors that we’d rather not remember, but having less sensitive sniffers would mean we’d miss out on the heavenly fragrance of lilies of the valley and the mouthwatering aroma of Grandma’s apple pie—and all the happy memories that accompany them.