Who Nose What’s Up with Olfaction?

If I had to pick a single smell that reminds me the most of home, it would be Twining’s Earl Grey Tea. It’s not so much the fragrance of the tea itself, but rather the smell of the packaging, that really makes me nostalgic. This yellow cardboard box, overflowing with gentle aromas of citrus and cologne, will forever remind me of sitting around the kitchen bench both before school and in the evenings with my Mum. Other favorite smells of mine include freshly baked rosemary bread, rain, a can of new tennis balls, and the bottom of my lemongrass and ginger candle. I also really like the smell of my dog’s paws. Man’s best friend has paws that smell strangely like tortilla chips – if you don’t trust me, smell for yourself. Evolutionarily-speaking, however, our sense of smell is necessary for more important things than merely experiencing joy after taking a whiff of a newborn’s head.

Essential for the identification of foods and dangerous situations, our sense of smell is crucial for survival. Think of your ancestors using the odor of a wild mushroom to determine if it’s toxic or not – feel free to take a moment to thank your lucky stars that they got it right. Without your nose, you wouldn’t be able to quickly and safely determine if the week-old milk in the fridge is safe or whether you left the gas stove on. Being able to smell is critical l for taste and can also be a friendly clue that its time you took a shower. Due to the negative consequences that accompany deficits in smell, a significant amount of research has been conducted on hyposmia and anosmia. Hyposmia and anosmia refer to the decreased olfactory function and lack of olfactory function, respectively (Knaapila & Tuorila, 2014). Little research, however has been conducted on the superabundance of smell, leaving hyperosmia in the dark.

In his national bestseller, The Man Who Mistook his Wife for a Hat, Oliver Sacks tells the enlightening clinical tale of a patient who experiences hyperosmia. Hyperosmia is defined as “better-than-average olfactory acuity.” One day, Stephen D., a highly successful medical student, got high on amphetamines and other hard drugs. That night, he had a vivid dream that he was a dog. Like most dogs, dream-world Stephen had a strong nose. Able to smell all of the rich smells in a way never experienced before, Stephen explained it was “as if [he] had been totally colour-blind before, and suddenly found [himself] in a world full of colour” (156). Interestingly, this transformative excess of smell persisted even when he awoke. In fact, his sense of smell was so profound that he was able to distinguish his friends and patients by their unique smell; these smells were even more vivid than were the visual images of their faces. As with dogs, with a simple sniff, Stephen was able to recognize fear and other emotions. This superabundance of smell, however, came to an abrupt halt after three weeks and never returned.

Sacks explains that this hyperosmia was likely a product of amphetamine-induced dopaminergic excitation. Essentially, the consumption of the amphetamines led to an excess of the neurotransmitter dopamine in Stephen’s brain. This excess of dopamine led to an increase in activity of certain brain networks, which can produce a stronger sensation of olfaction.

The red highlights the olfactory bulbs in the human brain

 

Not fully satisfied by this explanation (to Sacks’ credit, this book was published 30 years ago) and eager to further understand the neurological basis of hyperosmia, I took to the literature. As previously mentioned, little research has been done on hyperosmia as opposed to hyposmia or anosmia, but I was able to find one study (with help from my professor), which helped me to understand this phenomenon. Atianjoh et al. (2008), explain dopamine to be a type of olfaction ‘gate-keeper’ in the brain. With low dopamine, there is a lack of organization, which results in a chaos that hinders the brain’s ability to make sense of the different smells, impeding olfaction. Essentially, low dopamine means decreased olfaction. The image below depicts how different smells are organized in our olfactory systems, with each color receptor cell projecting onto its respective colour neuron. Following this, I interpret that excess dopamine would therefore increase olfactory organization, leading to a stronger sense of smell. This explanation aligns well with the neurological explanation offered by Sacks in the book. In Stephen’s case, consumption of amphetamines is what increased dopamine, thus perhaps increasing olfactory organization to produce hyperosmia.

This diagram highlights the complex organization of the olfactory system. The 1 points to olfactory bulbs.

Something that I’ve been pondering all week is the initial hyperosmia experienced in Stephen’s dream. One study I found suggests that olfactory dreams are very rare. In fact, of the 164 participants in this study and their 3372 dreams, only 1% of dreams contained olfactory and gustatory reports (Zadra et al., 1998). But for Stephen, tucked away in bed that night, excess olfactory sensations were incorporated into his dream. This dream might be a result of amphetamine-induced neurological changes that not only penetrated into his waking state, but also into his dream state. Thus, instead of dreaming of seeing water, Stephen dreamt of the “happy smell of water” (156). I wonder if Stephen’s dreams for the following three weeks all included increased olfaction. I would imagine that as the neurological changes were profound enough to persist into his waking life for three weeks, they would also affect his dreams for that time, too. While Sacks doesn’t write if these dreams continued to express heightened olfaction, he did, several years later, make one big reveal. Stephen D, is in fact, a pseudonym for the brilliant Oliver Sacks himself, who enjoyed drug experimentation on the weekends.

In my literature search I did find another interesting study worth mentioning. According to a study from Puri et al. (2014), there is an increased prevalence of hyperosmia in patients suffering from Lyme disease. Of the participant pool in this study, half of those suffering from Lyme disease exhibited hyperosmia. The researchers did not offer any neurological reasoning for this, shedding light on the need for more neurological research on hyperosmia. I’m not sure if I would enjoy experiencing this superabundance of smell or not. It seems that Oliver Sacks had a positive experience with hyperosmia, however, it did only last three weeks. I can imagine that some people have more negative experiences with this heightened sense of smell if it is more permanent. I must admit, it would be a cool “superpower” to be able to distinguish between family and friends by their smell…

References:

Atianjoh, F. E., Ladenheim, B., Krasnova, I. N., & Cadet, J. L. (2008). Amphetamine causes dopamine depletion and cell death in the mouse olfactory bulb. European journal of pharmacology589(1), 94-97.

Puri, B. K., Monro, J. A., Julu, P. O., Kingston, M. C., & Shah, M. (2014). Hyperosmia in Lyme disease. Arquivos de neuro-psiquiatria72(8), 596-597.

Zadra, A. L., Nielsen, T. A., & Donderi, D. C. (1998). Prevalence of auditory, olfactory, and gustatory experiences in home dreams. Perceptual and motor skills87(3), 819-826.

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