The Doctor Weighs In

By Dov Michaeli MD, Ph.D

A few days ago I received in the mail an unexpected package from Amazon. Not having had ordered anything from them, I was tempted for a minute to return it unopened, but then curiosity got the better of me –and what a surprise. It was a new book by my friend Lenny Karpman, a food writer and connoisseur about… chicken soup (“First, You Boil a Chicken”, available from Amazon). And what a gem it is!

But I am not here to promote a book. What I found strange was the physical reaction the title evoked: I literally smelled, heard and saw my mother standing next to a piping hot, steaming chicken soup with bubbling sounds coming out of the pot in the kitchen of my childhood. How can this be explained?

We all know that a smell can instantly transport us back to childhood or evoke pleasant or unpleasant memories, but now researchers in Israel believe they have found the reason why. In an experiment, scientists from the Weizmann Institute of Science in Rehovot led by graduate student Yaara Yeshurun tested a number of volunteers to see if their initial association of a smell with an experience would leave a unique and lasting impression on the brain. In a special smell laboratory, volunteers were shown images of 60 visual objects - including chairs and pencils (objects that are not normally associated with any smells), and at the same time were presented with either a pleasant or an unpleasant odor including pear, fungus, and dead fish, generated by a machine called an olfactometer.

The subjects were then placed in a functional magnetic resonance imaging (fMRI) scanner and asked to recall the smells associated with each image. The entire test was repeated 90 minutes later with the same images but different odors.

The scientists discovered that after a week, even if the volunteer recalled both odors equally well (both the pleasant and unpleasant), the first association revealed noticeably activated levels of brain activity in the hippocampus and the amygdala, areas of the brain associated with memory, learning and emotion.

The effect was so clearly defined that the researchers were able to predict how well a volunteer recalled smells eight days later, based on their first fMRI scans. They also found that unpleasant odors made the biggest first impression.

The experiment was also conducted using sounds rather than smell, but the scientists discovered that sounds did not arouse a similar distinctive first-time pattern of activity. Their research was published in the latest issue of Current Biology.

In her research article, Yeshurun says it makes good sense to remember unpleasant memories as a kind of evolutionary "risk management". "[It] may represent a potential adaptive mechanism considering the potential cost of failing to learn a first negative association and the potential benefit of a malleable first positive association," she and her colleagues write.

OK, I accept the conclusion that olfactory memories persist and that they quite logically confer an evolutionary advantage. But son et lumiere associated with the smell?

The paper does not deal with this question. But here is what we already know: the olfactory, auditory and visual areas in the brain are extensively interconnected. In fact, there is also an area where all those stimuli are integrated into a coherent context.

Can this be exploited clinically? Could psychiatrists of the future evoke long forgotten memories with smells, or sounds, or pictures in treating phobias or PTSD? I believe the answer is yes, and not in the distant future.

Oh, yes -about that chicken soup smell. Get the book and go to the section of your geographic, or ethnic, origin. Read it and smell the fragrance. Highly recommended.