Smells Like Yesterday

Originally published in the November/December 2002 issue of Today's Health and Wellness

Smells Like Yesterday

Olfactory memory: the emotional brain's answer to the time machine

by Kathy Monahan

It happens a lot around this time of year. Absorbed in the present, shop-ping for gifts or planning a holiday party, we are suddenly assailed by a ghost from the past: a scent. It may be a pleasant one of flowers or food, or a nasty one of burning or putrefaction, but it seems to catapult us into a memory so vivid that we are feeling the very emotions of an event years in the past.

Smell seems to grip our emotions more tightly than any other sense. Why is it that the scent of frying latkes can evoke memories of a beloved grandmother more than even a photograph? That the smell of evergreens can make us feel like children again even when we have grown children of our own?

The importance of scent

The connection of olfaction - the sense of smell - with memory is actually a directly physical one occurring in the limbic system of the brain, which governs emotion.

The olfactory bulb in the brain is only two synapses removed from the amygdala, the seat of emotional memory, and three synapses removed from the hippocampus, home of short-term memory. This nearness links the emotional brain to the smell receptors more closely than to any other sense.

Humans are animals, and we evolved our senses of smell for the same basic purposes as other animals did: to find food, to find a mate. The "good" smells of wholesome food and pheromones meant health, contentment and reproductive success; the "bad" smells of poison, putrefaction and predators could lead to catastrophe. The ability to assign meanings to smells - and to remember them - was very literally a matter of life and death.

Unlike the "lower" animals, which mark territory or signal readiness to mate by exuding odors, humans don't communicate with smell . . . at least, not consciously. There is evidence that the mating dance of humans is influenced by odor: men rate looks and smell as being equal factors in sexual attraction, while women rate smell even higher than looks. Mothers and infants also recognize each other by smell - not exactly communication, but certainly a link to our evolutionary heritage.

But in civilized society, we seek more often to mask or change odor with deodorants and perfumes than to use it to communicate. Taught that smell is primitive, we have lost our connection with its nuances.

Civilized humans gather most of their information about the world through the coded symbols of language: sight and sound. Smell, on the other hand, is so subjective that it almost defies language. Though humans can recognize almost 10,000 different odors, we can only describe a few.

Smell and memory

We most often associate smell with emotional memory, and in fact, much of the research that has been done with human subjects has dealt with emotional rather than objective memory. But the emotional influence of smell can even be brought to bear on non-emotional tasks: In one experiment, test subjects exposed to a certain smell while performing an unachievable task were more likely to fail at an achievable task when exposed to the "smell of failure" again.

However, experiments on animals show that odors bear on objective memory as well. Scientists have been able to teach rats and hamsters to perform spatial tasks by using smell; in fact, the learning curve on such experiments is so steep that most test subjects learn their tasks within two or three repetitions. Squirrels and chipmunks are especially expert users of objective olfactory memory; they use smell to locate cached seeds and nuts even when the cache is months old.

Scents influence mood

It's hard to imagine humans becoming sufficiently apt "smellers" ever to compete with the squirrels; if nothing else, we simply don't get the practice. But in recent years, we've grown more open to the idea of creating moods and stimulating emotions with smell; the booming business of aromatherapy bears witness to that. Scented oils, scented candles, scented lotions and soaps aren't just made to smell good any-more, but also to make us feel good. Essential oils have even been used with success as pain relievers, antiseptics and antidepressants.

Bringing scent into our own lives is easier than ever, with wide arrays of essential oils available at health food stores, beauty salons and boutiques. When choosing scents for their antiseptic or therapeutic properties, it's important to make sure you use natural essential oils. (You don't get the physical/chemical benefits of essential oils [antiseptic, pain-relieving] unless you use the real ones. Synthetics just smell nice.)

But it's easier than that to recapture a memory. Just light some candles, decorate your door with evergreens or put a batch of cookies in the oven, and the past comes rolling back.