One aspect of aromatherapy, which many massage therapists use in session, is its ability to take the client back to another time and place. Essence of rose, for instance, might remind one of a relative’s garden, while peppermint might evoke memories of presents under the Christmas tree, while a pot of peppermint tea bubbles in the kitchen.

Scientists at the Weizmann Institute of Science have now revealed the scientific basis of this connection. Their research appeared in the latest issue of Current Biology.

In a special smell laboratory, subjects viewed images of 60 visual objects, each presented simultaneously with either a pleasant or an unpleasant odor generated in a machine called an olfactometer.

Next, the subjects were put in an fMRI scanner to measure their brain activity as they reviewed the images they’d seen and attempted to remember which odor was associated with each. Then, the whole test was repeated—images, odors and fMRI—with the same images, but different odors accompanying each. Finally, the subjects came back one week later, to be scanned in the fMRI again. They viewed the objects one more time and were asked to recall the odors they associated with them.

The scientists found that after one week, even if the subject recalled both odors equally, the first association revealed a distinctive pattern of brain activity. The effect was seen whether the smell was pleasant or unpleasant.

This unique representation showed up in the hippocampus, a brain structure involved in memory, and in the amygdala, a brain structure involved in emotion. The pattern was so profound, it enabled the scientists to predict which associations would be remembered just by looking at the brain activity within these regions following the initial exposure.

“As far as we know, this phenomenon is unique to smell,” said graduate student Yaara Yeshurun, who participated in the research. “Childhood olfactory memories may be special not because childhood is special, but simply because those years may be the first time we associate something with an odor.”

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