The aroma of memories

I’ve been thinking a lot about memories lately. Yesterday when I was mowing the grass the mower ran over a small branch broken from one of our Peppercorn trees.

Sally Thompson photograph

Immediately the most astonishing thing happened, the smell hit my nostrils and triggered the most amazing memories of my grandmother and her home in Glen Iris. Beside the house in the next door yard was the largest peppercorn tree, and the limbs, which hung over the fence were used in a variety of ways. Sometimes a block and tackle was attached to remove a cars engine and other times there may have been a tyre swing. I have always loved the smell of peppercorn trees because they take me back to my childhood with my beloved grandmother.

When writing it’s important to give the reader a sense of smell, in book three there’s the smell of the dry wind blowing in from the desert, the smell of spices in a soup for dinner. At Khan el Khalili bazaar there are the smells of food, spices and incense and later at the chateau there’s the smell of newly mown grass. Just think how lost we would be without our sense of smell. Imagine not to be able to smell a BBQ cooking, and as a horse breeder, the smell of fresh shavings in the barn gives you a sense of knowing your horses have a safe, warm bed. What about the smell of rain on the dry earth? For a farmer that smell offers a huge feeling of relief.

I imagine we all have our favourite smells but I found this interesting article from www.serendip.brynmawr.edu to share…

SMELL AND MEMORY
Shigeyuki Ito
“When nothing else subsists from the past, after the people are dead, after the things are broken and scattered· the smell and taste of things remain poised a long time, like souls· bearing resiliently, on tiny and almost impalpable drops of their essence, the immense edifice of memory” -Marcel Proust “The Remembrance of Things Past”

Last week when I was in New York there was this good smell coming out of this restaurant and right when I smelled it, the smell brought back memories of this one festival I went to in Japan almost 3 years ago. On another occasion this perfume a girl was wearing brought back memories of a girlfriend in high school. Of all the senses I would say that smell is the sense that is best at bringing back memories. When you smell a certain scent it feels as though you slipped back in time and that you are actually at that scene again. If it was not for the other senses of your body, you might really feel as though you are back there again. But why is it that smell has this ability to instantaneously trigger memories of events, places or people that you usually would not “think” of?

Despite the tendency of humans to underestimate the role of smell in our every day lives, for most mammals, smell is the most important sense. Dogs are probably the most obvious example of this, it is through the use of the olfactory system that animals are able to find food, reproduce, and even communicate. While being one of the oldest and important parts of the brain, our failure to fully realize the importance of the olfactory system resulted in it being surrounded by numerous questions (2). How does it work? How do we identify smells? While these are only a few questions out of a whole list, research has progressed in recent years that we know much more about the olfactory system than before, but the fact remains that much remains to be found.

Through research conducted on mice, it is approximated that humans have 1000 different sensors in their nose (3). While this might seem like a large amount of sensors, it is not enough considering mice and humans can identify about 10,000 odours. The mystery surrounding this ratio can be explained through the unique features of the olfactory system. Odours are molecular so the method used is different from light or sound that come in waves (4).

Inside your nose about the level of your eyes, is a small patch of tissue containing millions of nerve cells. The odour receptors (sensors) lie on these nerve cells. Each of the receptors recognizes several odors, and likewise a single odour could be recognized by several receptors. Thus similar to codes, what happens is that different combinations of the 1,000 receptors result in our ability to identify 10,000 different odours. Linda Buck, an associate professor at Harvard, makes an analogy of this quite efficient system to letters being used in different combinations to make individual words. She goes on to say that this system ‘greatly reduces the number of sensors needed to code for the smells” (3).

The process that takes place is quite complex. After an odour molecule enters the nose and are recognized by the olfactory sensors, the signals are eventually sent to the olfactory bulb that is located right above the eyes (3). The signals only go to two areas in the olfactory bulb, and signals from different sensors are targeted to different spots that then form a sensory map. From there the signals reach the olfactory area of the cortex (smell sensory cortex) (5).

An important quality of the olfactory system is that information travels both to the limbic system and cortex. The limbic system is the primitive part of the brain that include areas that control emotions, memory and behavior. In comparison the cortex is the outer part of the brain that has to do with conscious thought. In addition to these two areas, information also travels to the taste sensory cortex to create the sense of flavor (2). Because olfactory information goes to both the primitive and complex part of the brain it effects our actions in more ways than we think.

Many wonder how certain smells able to trigger memories of events taking place several years ago despite the fact that sensory neurons in the epithelium survive for about only 60 days (1). The answer is that the neurons in the epithelium actually have successors. As the olfactory neurons die, new olfactory neurons generated by the layer of stem cells beneath them, which eventually takes the role of the old neuron as it dies. Linda Buck points out that the key point to the answer is that “memories survive because the axons of neurons that express the same receptor always go to the same place” (1). The memories are stored in the hippocampus, and through relational memory certain smells trigger memories.

Another popular question is the reason behind smell having such a strong role in instantaneously recalling memory. Despite our belief that sight and hearing are the two most important senses to our survival, from an evolutionary perspective smell is one of the most important senses. To recognize food or to detect poison, smell is the sense that almost all other mammals use. Because of this basic feature yet vital role, smell is one of the oldest parts of our brain. Trygg Engen, a psychology professor at Brown University notes that smells serve as “index keys” to quickly retrieve certain memories in our brain. This primitive yet essential role is probably why smells trigger memory more than does seeing or hearing.

Professor Engen goes on in attempting to further explain the relation of odour and memory. His controversial views basically states that the way we sense odours are all results of “nurture” and not “nature” (6). He says that initially all smells are neutral, and that whether a odour is pleasant or unpleasant has to do with the initial condition in which the smell is perceived. It follows from this that when we smell odours, it triggers a certain memory that has to do with that particular odour and thus is decided whether it is pleasant or unpleasant. Engen’s views are controversial because of the lack of convincing data to back his views up. Although certain points about Engen seem to make sense, such as how odour serve to trigger memories like index keys, his views about the “nurture” vs “nature” are a little harder to understand. If odours are decided by “nurture”, it leaves the question of how so many people have a similar view towards many odours. There is probably nobody who would say that the smell of rotten food is good. Yet Engen’s views are definitely worth considering because for some odours like gasoline, some people say it is good while others detest it.

It is said that people can identify about 10,000 different smells, but have many smells can you name off the top of your head (3)? In comparison, look at how many colours there are in a crayon box, or the many varieties of music existing. This lack of understanding and appreciation of odours is a result of our over reliance on our eyes and ears, even to the extent that we suppress our awareness of what our nose tells us. Our underestimation of the role of smell results in our lack of extensive knowledge concerning many aspects of the olfactory system. But as Proust stated, smell has such a strong power to vividly bring back memories, it is definitely more important than we realize. To a large extent smell is more personal than other senses so it brings back memories of people, not just places, or things.

This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be “authoritative” but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.