“What I remember most vividly is the aroma of toast at the old drugstore lunch counter. It was like no other. I don’t know why; we toasted the same white bread at home, but it never smelled as good or as intensely as it did in the drugstores. Maybe it was the high-volume buildup that did it. I loved that aroma. It made me feel good just to inhale it. Sometimes today, I’ll walk blocks out of my way to shop for something I don’t need at Kaufman’s on Lexington Avenue – the only pharmacy I know of that still maintains a real lunch counter – to drink in that toasty aroma” (qtd. in Engen 1991).
Sniff a rose or freshly cut grass. Scents evoke many images and sensations so common we don’t even give them much thought. The olfactory system, which senses and processes odors, is one of the oldest and most vital parts of the brain. 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 their primary mode of communication and influences many important functions, including reproduction and taste. Scientists are just beginning to learn how the olfactory system works.
At the time Rachel Herz began her work with Olfaction, there had been relatively few studies on odor and memory (Holloway 1999).
Researchers knew that the olfactory system was unique among the senses and that the primary olfactory cortex, in which higher-level processing of olfactory information takes place, forms a direct link with the limbic system, including the amygdala and hippocampus (Weiten 2000).
Researchers could also trace the physiological path
of a smell through the brain. It was known that after an odor molecule enters the nose and is recognized by the olfactory sensors, the signals are eventually sent to the olfactory bulb that is located right above the eyes (Passer 2001).
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 (2001).
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 includes areas that control emotions, memory, and behavior. In comparison, the cortex is the outer part of the brain that deals with conscious thought. In addition to these two areas, information also travels to the taste sensory cortex to create a sense of flavor (2001).
It was thought that because olfaction goes to both the primitive and complex part of the brain, it effects our actions in many ways.
Herz’s work, examining the underpinnings and implications of odors, has shown that odor is an important and potent memory cue – but that it is better for recalling emotion than for recalling fact. She has explored, among other things, sexual differences in smell and mate selection, the role odor can play in performance on tests, hemispheric variations in the perception of scents and the influence of words on how we sense smell (Holloway 1999).
Her work with Trygg Engen revealed that only two synapses separate the olfactory nerve from the amygdala, which is involved in experiencing emotion and also in emotional memory (Engen 1991).
In addition, only three synapses separate the olfactory nerve from the hippocampus, which is implicated in memory, especially working memory and short-term memory. Olfaction is the sensory modality that is physically closest to the limbic system, of which the hippocampus and amygdala are a part, and which is responsible for emotions and memory (1991).
Indeed this may be why odor-evoked memories are unusually emotionally potent. Herz’s work also shows significance that olfactory neurons are unmyelinated, making olfaction the slowest of all senses. It not only takes the brain longer to perceive olfactory stimuli; the sensation of odor also persists for greater lengths of time than do sensations of vision or audition (1991).
There had been compelling evidence that the excellence of odor memory is not based on its capacity for storing information. It was believed that the number of odors in the memory of an average person is not known, but visual and auditory capacities are probably much higher. According to Engen, the sense of smell has limited access to what is stored in its memory (1991).
The first dictionary definition of memory is the ability to recall physically absent items – a date, a tune, a face – but this is not possible with the sense of smell. A physically present odor is required to activate this memory system, and as Nabokov said, “Memory can restore to life everything excepts smells, although nothing revives the past so completely as a smell that was once associated with it” (1970).
Herz’s work shows that the emotional aspect of odors is much more powerful in the presence of the odor itself (Holloway 1999).
Odors are not recalled by words, images, or other items. Instead, they help recall experiences and emotions. When people talk about the odors they remember, they are referring to experiences and situations in which odor played an important part. They remember the seasons and the fact that spring brings fragrances with it. However, only the visual attributes are recalled; recreation of the fragrances is not itself part of the recollection. Herz explains that touchy-feely objects in a box and verbally indescribable music don’t evoke the same emotional memory or provoke the same increased heart rate that smell does (Holloway 1999).
Some of Herz’s most compelling evidence for emotional memory was her work with Gisela Epple, in an experiment that used smells to manipulate emotions and performance of a feasible task. Their findings were that children who smelled “failure” did much worse on the second test than did those who were not smelling the initial odor or were smelling a new one (1999).
With this knowledge, students and teachers could manipulate a class’s mindset by releasing a pleasant odor during a simple task to instill a “successful” train of thought, and then repeat the odor on a more difficult or complex task. It is much like newborn children learning through association and by developing theories. The first is always based on emotions – warm feels safe. It is then modified by desire – I want to be warm. Then perception – Mommy is warm. And finally belief – Mommy is safe. Like smell and a successful mindset, each theory builds upon the proceeding theory, and all are changeable with new discoveries and data. Thus, our emotions and knowledge increase with experience.
This emotional potency makes complete sense, Herz argues her evolutionary theory, given that in the beginning there was smell: organisms used chemical sense to move toward the good (food) and away from the bad (predator).
Because the limbic system grew out of the olfactory system, the emotional dichotomy between good (survival, love, reproduction) and bad (danger, death, failure) reflects the chemosensory one (1999).
Odor memory serves the primitive protection function making sure that significant events involving food, people, or places are not forgotten. While visual and auditory memory usually decrease with time, often exponentially in light of new experiences, odor memory remains intact (Weiten 2000).
Although Herz’s work is ground breaking, many mysteries about odor and memory remain. These and other discoveries are leading to important insights about human behavior and providing hope for treating those with a diminished or lost sense of smell.