Nothing to Sniff At : There are odors that make us smile--and make us turn up our noses. But did you know that some can speed learning or improve memory? That’s the theory, anyway.

Dr. Alan Hirsch has a vision of the future. You can’t see the vision, but you can smell it.

“Ten minutes before you wake up, your alarm clock will release a puff of a wake-up smell,” says Hirsch, a neurologist, psychiatrist and maverick scientist of smell. “At work, there will be odors to reduce the chances of errors. After work, an odor to relax. At the gym, an odor to increase exercise strength. And later, an odor to eat more or less.”

In the evening, Hirsch says, “there will be an odor to make you more amorous.” And then, he says, “one to help you sleep better.”

Hirsch, who heads the Taste and Smell Research Foundation in Chicago, is one of a growing number of doctors, psychologists and molecular biologists turning their attention to the sense of smell.

Their target is elusive. Of all the body’s senses, smell is probably the most difficult to study and the least understood. Yet, it may be the most broadly influential, affecting our moods, memories, problem-solving abilities--not to mention our sexual appetites and choices of mates.

“The field of smell is an enormous untapped field, especially for how it affects people’s behaviors and emotions,” Hirsch says.

That’s starting to change. This spring, Hirsch reported results of a study indicating that men are sexually aroused by the combined smell of lavender and pumpkin pie much more than they are by traditional perfume fragrances. Other recent work by Hirsch has suggested that certain smells can speed learning, improve memory, help in weight loss, affect aggression levels and even alter one’s sense of how big a room is.

Hirsch’s findings remain preliminary and are rejected by some experts as oversimplified. But other studies also have begun to hint that odors may have a pervasive, if largely ignored, influence on day-to-day life.

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The intimate linkage between odors and emotions is mostly a matter of biological wiring. Vision, hearing, taste and touch send their sensory input to the front of the brain, where logic and cognition can rationally interpret the information. By contrast, smell has a direct line to the limbic system, the primitive “reptilian” part of the brain that generates our most basic emotions: fear, rage, affection, lust.

Of course, people have known for a long time that scents--whether made by glands in the body or by scientists at Chanel--can have a powerful influence on feelings and behavior. Perfumes have been around for centuries. And Freud hypothesized that human civilization could never have developed had we hairless apes not gradually lost our animal olfactory sensitivity, freeing us from the otherwise unavoidable obsession with the smells of sex and violence in the air.

Yet only in the past few years have scientists moved beyond old-fashioned studies that simply looked at how people responded to certain smells and started to explore the biological and neurological nature of smell.

“Fragrance research can be a sort of froufrou discipline on its own,” says Avery Gilbert, a biopsychologist and president of Synesthetics, an odor consulting company in Montclair, N.J. Just look at the many “aromatherapy” products that now fill the shelves of health-food stores, he says, few of which have been validated with any real scientific rigor. “Now we’re coming out of the dark ages with smell. We are really getting a better grip on how smell works in our daily lives.”

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Smell accounts for about 90% of what we think of as taste, but smell is not like taste, experts say. While bitter flavors are rejected by almost everyone and sweet ones are universally liked, preferences for certain smells--and many of the personal effects of those smells on mood or behavior--vary considerably among individuals. This is probably as a result of positive or negative experiences that different people associate with those smells from early in life.

Research has clearly shown that smells make strong impressions from the first days of life. Within a week after birth, for example, infants offered two identical pieces of clothing show a clear preference for the one that has been worn by their mother, turning their head in the direction of the cloth and stretching toward it. Similarly, mothers can distinguish by smell alone between a T-shirt worn by their child and one worn by another.

Moreover, those recognition patterns may last forever. Michael Leon, a neuroscientist at UC Irvine, has shown that in infant rats, at least, the part of the brain that responds to smell undergoes subtle but permanent structural changes during that early period of mother recognition, as though the smell pattern were getting “hard-wired” into neurological memory.

Researchers are hoping that a closer look at the molecular biology of smell will show that some odors affect most people in similar ways, a finding that would open the door to the rational engineering of our odor environment according to the rules of a new science Gilbert calls “the ergonomics of smell.”

Already, molecular biologists are sifting through the recently discovered odor-receptor genes to learn exactly how the nose--which can detect about 10,000 odors--responds to smell.

Who knows what’s possible? In one striking set of experiments, Susan S. Schiffman, a professor of medical psychology at Duke University, recently found that by spiking foods with aroma enhancers, she could strengthen the immune systems of elderly people who ate the food.