Sniffing out memories of holidays past

Sniffing out memories of holidays past those induced by other stimuli, they he smell of a small cake dipped are perceived as being more accurate in tea helped propel author because of their emotional quality, Marcel Proust back to childhood, she continues. In a recent study, triggering a vivid memory of Sunday Herz randomly associated visual, mornings spent with his aunt. auditory, tactile, and Similarly, odours olfactory stimuli with associated with the emotionally arousing winter holiday season pictures. “Odours —eg, pine needles, were equivalent to candles, and the other stimuli in warm smell of spices their ability to elicit —often evoke poweraccurate recall”, she ful memories of past says, “but memories celebrations. evoked by odours “There’s somewere always more thing uncanny about emotional”. the ability of an Richard Doty of odour to elicit a the University of memory that recrePennsylvania Smell ates the entire and Taste Center ambiance of an expe- Triggers for potent memories (Philadelphia, PA, rience”, says Linda USA) suggests an additional mechaBuck of Harvard Medical School nism that may, in part, explain (Boston, MA, USA), who studies Proust’s experience. Throughout life, odour receptors and the neural pathhe says, “you are regularly bomways of olfaction. “Most of us have barded with shapes and sounds simihad that experience with a smell, but lar to those which you may have tied it’s not clear why.” Several theories a memory to when you were young. are emerging to explain the phenomThere is a tendency for these stimuli enon, however. In olfaction, says to lose their uniqueness and permaBuck, signals from sensory neurons nence over time, and thus the experiin the nose are transmitted to the ence originally remembered loses its olfactory bulb from where they are uniqueness”, he explains. “But an relayed to the olfactory cortex, an odour may be different. You may area of the brain which includes the smell something once but not again amygdala. The olfactory cortex then for years. Then one day, you smell it, sends signals to the higher cortical and say, ‘oh, my grandmother’s areas and the hypothalamus. “The pantry’. So odours may evoke memolimbic projections to the amygdala ries simply because you don’t come and hypothalamus are thought to be across them very much.” particularly important to both the Similarly, if you experience an emotional and motivational effects of odour only once a year—at odour, but all we know for sure is Christmas time, for instance—then that there is a general association”, that smell is likely to be tied to the says Buck. yearly occasion. This connection can Rachel Herz (Monell Chemical be used commercially, says marketing Senses Center, Philadelphia, PA, expert Gary Bamossy (University of USA) is convinced that the links Utah, Salt Lake City, UT, USA). between the olfactory and limbic “We frame it in terms of classical systems are responsible for odourconditioning—a stimulus–response induced emotional memories. “No model. Smell really does cue a lot of other sensory system has direct access strong emotions and memories, and to the amygdala. And, from a neuromarketers like that kind of response anatomical–evolutionary perspective, because it gets people to move from a the limbic system literally grew out passive mode to one of strong behavof the olfactory bulb. So there is a ioural intention or actual behaviour.” fundamental connection between So, during the holiday season many these two brain areas, both functionsupermarkets have in-store promoally and anatomically”, she asserts. tions that involve cooking. Although “If you’re exposed to an odour and expensive and time-consuming, an event, and you’re in an emotion“during the holidays they’ll do it ally primed or heightened state, then because it promotes sales. If people that event will be tightly fused with experience traditional smells that the odour in memory.” evoke strong emotional responses, Although memories induced by and they are where they can buy odours are no more accurate than

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turkey or cranberry sauce, then they will”. Richard Axel of Columbia University (New York, NY, USA), adds another dimension to the odour–emotions–behaviour equation. Many odours are universally perceived “in the same judgmental way”, he observes. Although there are some individual differences in odour perception, he says, “there also must be significant hardwiring—genetically programmed responses leading to specific behaviours”. An example is the smell of smoke, an odour which leads to avoidance behaviour in all animals, including human beings. If odours are intertwined with emotions, memories, and behaviours, what happens when olfaction is impaired? For one thing, quality of life is impaired, says Doty. “The sense of smell is something people take for granted. If they discover when eating a holiday meal that the food has an ‘off’ smell, but everybody else says it’s fine, then they will wonder what’s wrong with them.” Yet smell dysfunctions of this nature are particularly common in the winter when upper respiratory infections damage the olfactory membrane. In addition, reduced smell is an early sign of Parkinson’s and Alzheimer’s disease, notes Doty, who recently designed an odour-memory test—an extension of the University of Pennsylvania Smell Identification Test—for use by researchers studying neurodegenerative diseases. Loss of smell also puts people at risk for not being able to detect smoke, leaking natural gas, and similar dangers. “There’s a whole safety issue, particularly for older people living alone, which can lead to feelings of isolation and depression”, he says. It is estimated that a marked decrease in the ability to smell affects 50% of all people aged 65–80 and 75% of those older than 80. But for those whose sense of smell is intact, there is something to look forward to next year. A desktop “scent synthesiser” will add odours to web sites, e-mail, movies, music, e-commerce, and interactive games, says DigiScents’ Joel Bellenson. “Scent is a powerful way to reinforce ideas”, he says. “If a picture is worth a thousand words, a scent is worth a thousand pictures.” Beta testing of the synthesiser starts soon (http:// www.digiscents.com). Marilynn Larkin

THE LANCET • Vol 354 • December 18/25, 1999