How some aromas are bound in memories

REHOVOT, Israel, Nov. 10 (UPI) -- Authors and screenwriters have long been aware that some odors can spontaneously evoke strong memories, but Israeli researchers have explained why.

Graduate student Yaara Yeshurun with professors Noam Sobel and Yadin Dudai of Weizmann Institute of Science in Israel said the key might not necessarily lie in childhood aromas but rather in the first time a smell is encountered in the context of a particular object or event.

In a special smell laboratory, study 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 a functional Magnetic Resonance Imaging 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 with the same images, but different odors accompanying each.

The subjects came back one week later to be scanned in the fMRI again as they viewed the objects one more time and were asked to recall the odors they associated with them, Yeshurun said.

The study, published in the Current Biology, found that after one week, even if the subject recalled both odors equally, the first association revealed a distinctive pattern of brain activity, whether the smell was pleasant or unpleasant.