Smell is the only sense for which an entirely new stimulus can be created artificially. Chemists frequently design novel molecules with physicochemical structures unknown in nature, sometimes with heretofore uncharted sensory qualities. This is unlike vision or audition where sensory receptors pick up stimulus features within a well-defined range of electromagnetic wavelength or frequency. In contrast, smell possesses all the hallmarks of an open system where the nose cannot predict the features with which it comes in contact. But how does the brain make sense of a stimulus space with unknown boundaries that are still expanding?And how does the brain enable the mind to translate this information into odors? My research focuses on these questions and how the answers to them can generate a new model for theories of mind and brain. Smell encompasses a vast array of scientific fields, from psychology to neuroscience to chemistry, as well as humanities, such as philosophy of mind, cultural history, and anthropology of food. This inherent multidisciplinarity of my topic clarifies my scholarly trajectory, which began with philosophical investigations and developed into experimental practice in my newly finished laboratory.
I am an Assistant Professor with a joint appointment in History and Philosophy of Science and Medicine and Cognitive Science since 2019. During this period, a significant global event occurred. In a cosmic twist, Covid confirmed and accelerated my work. Loss and distortion of smell was a critical symptom of the initial variants. When I discuss my research, the first question I am now asked is no longer “Why would you study smell?” but rather “So, how does it work?”. I answer: “That is indeed the question!” To be sure, not knowing a definite answer to this question is not the same as not knowing. Prior investigation faltered because it was founded on an incorrect premise, namely that the olfactory system should function like our paradigmatic sense, vision. My model, which arose from my philosophical studies, is currently being implemented in experimental designs in pursuit of a genuine alternative.
My past analytic work investigated why olfaction was disregarded by scientists for centuries, despite its vital role in animal foraging and mating behavior, and why it remains methodologically challenging to study smell experimentally to this day. I began this work with my Ph.D. at the Centre for the Life Sciences at the University of Exeter, UK (2010/13), and deepened it during my two postdoctoral research fellowships, first at the Konrad Lorenz Institute for Evolution and Cognition Research in Vienna (2013/15) and then as a Presidential Scholar in Society and Neuroscience at Columbia University in New York (2015/18). My ‘experimental turn’ was initiated at Columbia where I was based in the laboratory of the neuroscientist Stuart Firestein, and it gained traction and reality during my year as Visiting Assistant Professor in Cognitive Science at IU (2018/19) prior to starting a tenure-track position here. The results of my research conducted during these years have been accepted and published in several highly rated peer-reviewed outlets (to date: 19 journal articles and 8 book chapters), including scientific journals such as Cell, Journal of Theoretical Biology, Frontiers in Neuroscience, Frontiers in Psychology, New Ideas in Psychology, and philosophy and history of science journals such as Biology & Philosophy, History of Science and Humanities, Perspectives on Science, Journal for the General Philosophy of Science.
My investigations uncovered a paradoxical fact. It turned out that the very features that led people to ignore olfaction in the past are the same characteristics that make it interesting to neuroscience and cognition researchers today. First, individual odor perception is highly variable between individuals. Second, volatile airborne compounds are challenging to control from an environmental standpoint and, compared to vision, harder for the brain to anticipate and ‘predict’. This context dependence makes olfaction an excellent model to better understand sensory learning and its connection with cognition, including memory. The turning point for olfactory research and spark that ignited interest in the workings of smell was the identification of the odor receptor genes in 1991 by Linda Buck and Richard Axel, who were awarded the 2004 Nobel Prize in Physiology or Medicine for their discovery. This could have been the end of the story. However, instead of leading to conclusive answers, this discovery opened new lines of inquiry. Instead of explaining the mechanics of odor perception by filling in the gaps based on established models of vision, the olfactory system demonstrated that it worked differently than other senses, including audition and somatosensation. My philosophical interest was to understand the complex dynamics in a research area at the crossroads between tradition and revolution. The results of my work led to my monograph “Smellosophy: What the Nose Tells the Mind” (Harvard University Press, 2020). Smellosophy is widely acclaimed. It received extremely favorable reviews in prestigious scientific journals such as Science and philosophical journals such as Mind, and several international magazines, including The Wall Street Journal, Harpers’ Magazine, Times Literary Supplement, The Spectator, la Repubblica, and De Standaard. It was further mentioned in The New York Times (twice), The Irish Times, Vox, Elle Canada, Svenska Dagbladet, and in 2020 it was listed as an NRC Handelsblad Best Book and the Telegraph’s “Best Wine Books for Christmas.” Smellosophy was turned into an audiobook and paperback. It is translated into Japanese and Korean (where the book-jacket blurb was written by Bong Joon-ho, 2019 Oscar winner for the movie Parasite). It is presently being translated into Arabic and Polish. The book was a turning point in the public recognition of my work. Increased interest in the sense of smell during the pandemic led to prominent science communication engagements, including TEDxCambridge (online release pending), an interview with Sean Carroll on Mindscape, interviews aired internationally on BBC, ABC/Australian Broadcasting Corporation, RNZ New Zealand, locally on WFIU Profiles, and several science communication pieces that I wrote for Nautilus, Aeon, and Neo.Life.
Moreover, the research for my book served as a catalyst for current and future work. I interviewed 45 olfactory experts over 3 years for Smellosophy, including Nobel laureates Buck and Axel, renowned perfumers including Christophe Laudamiel (creator of fragrances such as Polo Blue) and Harry Fremont (co-creator of CK One), and other pioneers in the field. This provided me with a unique perspective on the nature of smell and its multidisciplinary character. It also served as the backdrop for the development of my model of smell as a dynamic system that cannot be explained using conventional stimulus-response models and the mapping of neural correlates. Remarkably, a 2021 paper from the Axel lab discovered ‘representational drift,’ which means that the neurons in the olfactory cortex that respond to an odor change entirely over the course of 1 month, supporting my hypothesis that smell cannot be modeled via stable neural correlates. While the brain is known to change, representational drift revealed a hitherto unconceived rate and speed of change! This is unlike anything we have known from vision or audition. Drift had only been observed in “higher-level” learning domains, not in sensory cortices. But if there is no stable neural population assigned to identify a specific odor, how does the brain know what it’s smelling?
This leads me to conclude with my laboratory, which our group nicknamed ‘The Stink Tank.’ We combine olfactometry (involving a custom-built instrument for the controlled measurement of odor responses) and EEG (electroencephalography). Currently, the lab pursues 4 projects.
I am the lead of the 1st project that pursues a deceptively simple question: Does the brain classify odors according to their chemical or biological similarity? This research builds on recent work by the Firestein lab, which revealed that receptors and chemists do not model odor similarity using the same physicochemical features, and for which I designed an experiment to measure neural responses in response to stimuli of varying similarity. The 2nd project, conducted by Gabe Severino, focuses on the capacity for neurogenesis (the formation of new neurons) in adult olfaction—another characteristic exclusive to smell compared to other senses! Severino is developing a predictive computational model of cell lineages of the olfactory epithelium to be implemented in living cells. The 3rd project is conducted by Irene Georgiadis and co-supervised by Prof. Rich Shiffrin. Her research compares odors to visual and auditory stimuli in tests of working memory. All projects share a common theme: To understand smell we must develop models based on the particularities of the olfactory system, not generic models derived from vision. The 4th project is conducted and currently developed by Jag Williams (more soon).
My research has a bold but sincere long-term objective. Most contemporary models of consciousness are based on visual awareness. But what if we looked at the sense that sits at the threshold of conscious awareness? What if we investigated awareness in consciousness with olfaction instead?
Image from H. Zwaardemaker, Die Physiologie des Geruchs (1895), depicting Paulsen's 1882 experiments of airflow patterns in the nasal cavity.