Scent

What really makes a memory vivid in your mind? Most of the memories that I have, I can remember what I see, sometimes I can remember some things that I heard. But the memories that are the most lifelike are the ones in which I can remember the smells. The sense of smell, olfaction is closely related to taste and also has a very strong influence on emotions. However, beyond these functions smell is also essential for finding food, avoiding dangerous things and finding a mate. I think that smell is often the most overlooked sense that we possess. If you have ever asked someone what sense they would give up, it is often between taste and smell for the sense that is given up. Often people don't recognize the importance or the experience of smell until they are sick and have a stuffed nose. I want to take the time now and talk about how important this sense is to me.

I first started to understand the importance of smell a few years ago when I read the book, The Emperor of Scent. The story describes a scientist (who is also a connoisseur of the nose) proposing a theory about how we smell and the process that he goes through to publish and also propose his theory to the scent makers. It was here that I began to recognize all that I take my sense of smell for granted for.

Olfaction actually occurs through the binding of molecules to the olfactory epithelium. This ligands stimulate olfactory receptors on the dendrites of olfactory receptor neurons. This occurs either through diffusion or through binding to specific proteins. This action triggers a cascade of second messengers mediated through g-proteins. The specific pattern of conformational changes of the proteins paired with the specific pattern of chemical changes maps onto a cognitive map of axonal activation which describes a broad range of aromas. The activation of certain projections will produce the sense of different smells depending on which projections are stimulated or depressed. The sense of smell is interesting because to some extent it is the only sense which uses direct stimulation of the nerves. The projections of the olfactory neurons combine to form the olfactory nerve. The synapsing of the projections in the olfactory bulb begin the process of divergence for the projections of the olfactory system. Some projections continue on to the olfactory cortex, while others converge into glomeruli which are composed of Mitral cells. These cells synapse onto five other area of the cerebrum, including most importantly the amygdala and the entorhinal cortex. The entorhinal cortex projects to the amygdala which is involved in the emotion of the sense of smell and it also projects to the hippocampus which is involved in the memory of smell. The close ties of the olfactory system with the limbic and memory systems place the importance of smell in emotional and place memory.

Before going into deeper detail here, I want to mention some of the other functions of smell. Combining the sense of smell with the sense of taste produces flavor. It is amazing to think that there are essentially five different tastes but hundreds of smells, thus to produce a certain flavor, a different combination of smells is used with a base layer of tastes. This technique of alteration is how we are able to produce countless numbers of candies and soft drinks.

Another important function of olfaction is the detection of pheromones. Pheromones are a chemical signature which causes a reaction in other members of a species. Related to humans, I speak of sexual pheromones. During ovulation a women's sense of smell is the strongest. This relates to the results that olfaction is used to detect the MHC genes which are useful in the immune system. Partners look for a partner to have a different MHC gene combination so as to strengthen the immune system of their offspring.

Back to the emotional and memory connections of smell. Its odd how a quick whiff of a smell can almost literally transport you back in time to a specific memory. The use of smells in certain situations seems to take advantage of the emotional connections of smell and memory. From the use of perfume or cologne for special occasions or the cooking of special meals for occasions help to strengthen memories by using this olfactory pathway which connects the amygdala and the other memory systems. Smell seems to be the only other sense which can elicit such strong memories in my mind besides hearing, specifically music. There are a few songs which seem to be able to take me back to a memory, but it is the smell of certain odors which seem to bring me back and almost relive a memory. While the perception of smell is not understood completely, it will be very interesting to uncover the mysteries of the sense. It is interesting however, to take advantage of the effects of smell on memory, one that can be useful creating great memories for life.

That Smell - Lynyrd Skynyrd