How Smells Influence Our Hormones, Health & Behavior | Huberman Lab Podcast

Podcast Host: Dr. Andrew Huberman (Stanford Associate Professor - brain development, brain plasticity, and neural regeneration and repair fields)

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Podcast Guest: Dr. Noam Sobel (Professor of neurobiology in the Department of brain sciences at the Weizmann Institute of Science)

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Key takeaways

Olfactory training and nerve regeneration are potential ways to recover a lost sense of smell (segment 03).
Humans possess remarkable olfactory abilities, and research shows that separate nostrils perform better (Segment 06).
The nasal cycle is related to the autonomic nervous system and can be measured with wearable technology (Segment 07).
Nasal inhalation is linked to cognitive processing and can enhance performance on tasks (Segment 08).
Congenital anosmia is a rare condition that can lead to social difficulties and decreased lifespan (Segment 10).
The benefits of meditation include stress reduction, improved focus, and increased emotional regulation (Segment 13).
The study highlights how social chemo signaling plays a sex-specific role in human aggression (Segment 16).
Social interaction influences menstrual cycles; synchronization may enhance the likelihood of conception in groups (Segment 17).

Summary:

In this podcast, the featured guest is Dr. Noam Sobel, a distinguished academic with a Doctor of Philosophy degree and a professorship in neurobiology within the Department of brain sciences at the prestigious Weizmann Institute of Science. In his discourse, Dr. Sobel expounds on his laboratory's scientific investigation into the biological underpinnings of olfaction. He provides a comprehensive account of how the detection and recognition of odor molecules and chemical compounds in our surroundings have a profound influence on various aspects of human behavior, cognitive functions, social interactions, and endocrine responses. Within this discourse, Dr. Sobel elucidates the significance of olfaction in the concept of "social sensing" and its role in discerning the physiological and psychological attributes of individuals during initial encounters. Dr. Sobel offers further elucidation concerning the implications of this phenomenon regarding the establishment of social bonds such as friendships and romantic relationships. Dr. Noam conducts a comprehensive examination of the impact of olfaction on diverse domains, including affective states, endocrine function, memory processes, and the interrelationship between respiration and autonomic control. Dr. Sobel expounds upon the prospective utility of olfactory screening examinations in the context of disease diagnosis and elucidates upon his research team's endeavors to digitize the sense of smell. The hypothetical advancement of a technology that enables the transmission of odors through the internet possesses the capacity to substantially alter the domain of digital communication. According to Dr. Sobel's research, the sense of smell in humans displays a significant level of sensitivity and has a considerable influence on various aspects of our physiology and behavior.

(01). 00:00:00 Dr. Noam Sobel

Dr. Noam Sobel is a distinguished faculty member in the field of neurobiology, holding a professorship at the esteemed Weizmann Institute of Science in Israel. His research group is focused on investigating the intricate mechanisms underlying olfaction and chemosensation. The research conducted by Professor Sobel centers on the intricate nature and neural mechanisms of the human olfactory system. This system is not only responsible for our sense of smell, but also plays a crucial role in fundamental social interactions, emotions, and memories. The malfunctioning operations of this particular system may serve as an indicator of initial indications of cognitive and neurological decline, such as those observed in Alzheimer's and Parkinson's ailments. The team led by the individual in question spearheaded the advancement and fabrication of olfactometers, which are instruments that accurately produce scents. Additionally, they played a role in the progression of "electronic noses," which are devices that emulate the olfactory capabilities of animals by converting molecules into perceptions. Through the utilization of these devices, the research team was able to uncover various fundamental principles in the field of olfactory neurobiology. Specifically, they were able to devise a quantitative measure for assessing odors and forecasting the corresponding neural reaction. Additionally, the team identified a chemical compound present in human tears that elicits a range of physiological responses upon inhalation, including a decrease in testosterone levels.

The olfactory system is responsible for the perception of odors, whereas chemosensation refers to the physiological and behavioral responses to chemical stimuli in the environment. In the present session, we shall acquaint ourselves with some remarkable insights about the manner in which individuals engage with their surroundings and fellow beings. In this context, it is noteworthy that humans possess the ability to detect odors in their surroundings, much like dogs. It is worth noting that humans exhibit remarkable proficiency in perceiving the chemical environment around them. Additionally, upon encountering an individual, humans tend to absorb chemicals emanating from the individual's chemical cloud or surface, and subsequently analyze the information gleaned from these chemicals to make inferences about the individual, such as their stress levels and hormone levels. Dr. Sobel will also provide insights on the subject of tears, specifically how the tears of others can significantly affect one's hormone levels. It will also be learned that periodic alternation of ease occurs, allowing for unilateral respiration through either nostril. The laboratory of Dr. Sobel has made remarkable discoveries, which will be expounded upon in great detail for your learning [1].

References

1. Prof. Noam Sobel. Available from: https://www.weizmann.ac.il/conferences/InternationalBoard2015/prof-noam-sobel.

(02): 00:06:46 Olfaction Circuits (Smell)

Humans perceive odors through two distinct processes: orthonasal olfaction and retronasal olfaction. Orthonasal olfaction is the primary process by which odorants are detected through the nostrils. However, humans also perceive odors through retronasal olfaction, whereby odorants travel up through the back of the throat and into the nasal cavity, allowing for the perception of odors through the mouth. This process is particularly important for the perception of food and taste, as it contributes significantly to olfactory input. Airborne molecules traverse a distance of approximately six to seven centimeters into the nasal cavity, where they engage with the receptors present on the olfactory epithelium. The number of olfactory receptors in the human nose is estimated to be around seven million, indicating a significant proportion of the genome is dedicated to encoding the various subtypes of olfactory receptors. The notion of the existence of seven million receptors is a fabricated construct that lacks support in academic literature and textbooks and is disseminated without empirical basis. The aforementioned is the sensory surface of the olfactory epithelium. Odorants engage with the receptors located in the nasal epithelium, leading to a process of transduction.

The olfactory cilia house the cellular and molecular apparatus responsible for olfactory transduction. The process of odorant transduction is initiated by the binding of odorant molecules to particular receptors located on the outer surface of cilia. Odorant binding can take place either through direct binding or via odorant-binding proteins present in the mucus. These proteins sequester the odorant and facilitate its transportation to the receptor. Subsequently, a receptor potential is produced through the activation of ion channels via supplementary steps. The predominant pathway in mammals entails cyclic nucleotide-gated ion channels, which bear resemblance to the ones present in rod photoreceptors. Olfactory receptor neurons are equipped with a distinct type of G-protein, known as Golf, that triggers a specific adenylate cyclase unique to the olfactory system. The elevation in cyclic AMP (cAMP) leads to the activation of channels that facilitate the influx of Na+ and Ca2+ ions (predominantly Ca2+), thereby inducing depolarization of the neuron. The process of depolarization, which is intensified by a Cl- current that is activated by Ca2+, is transmitted in a passive manner from the cilia to the axon hillock area of the olfactory receptor neuron. This leads to the generation of action potentials, which are subsequently conveyed to the olfactory bulb.

The olfactory bulb in humans is a point of interest due to its sensitivity. Trauma or impact to the front of the head can result in loss of the sense of smell, which is a common occurrence. However, the more typical cause of this loss is trauma to the back of the head, known as contra coup injury. The brain is suspended in cerebrospinal fluid (CSF) and when it experiences an impact to the back of the head, it moves forward and backward within the skull, potentially crushing against the front of the skull. This phenomenon generates a shearing motion on the crib form plate, which can sever the olfactory nerve [2].

Figure 1. Olfactory Transduction [2].

References

2. Purves D, A.G., Fitzpatrick D. Neuroscience. 2nd edition. 2001; Available from: https://www.ncbi.nlm.nih.gov/books/NBK11039/#:~:text=Odorant%20transduction%20begins%20with%20odorant,shuttle%20it%20to%20the%20receptor.

(03): 00:14:49 Loss & Regeneration of Smell, Illness

In cases where the nerve is fully severed, the resulting anosmia is a permanent condition. The complete loss of the sense of smell is accompanied by regeneration at the basal cell level at epithelium. In case of partial loss or the emergence of residual function shortly after the injury, there exists a favorable possibility of recovery. The axons grow along the trajectory of other axons. It is noteworthy that in the event that an individual does not regain their sense of smell within a year, it is unlikely that they will ever recover it. The process of olfaction involves multiple sensory subsystems, rather than relying solely on the olfactory system. The human nose contains several chemosensory sensitive nerves, including the trigeminal nerve, which is the fifth cranial nerve. This nerve is located behind the olfactory nerve and has sensory endings in the nose, throat, and eyes. The perception of odor is triggered by the activation of the olfactory nerve, whereas the activation of the trigeminal nerve results in a variety of sensations such as irritation, freshness, stinging, prickliness, burning, and tingling. These sensations can be collectively referred to as pungent sensations. The trigeminal reflex is responsible for the pungent odor and the irritating effects on the eyes and throat that are commonly associated with onions. This can be attributed to the fact that onions possess three distinct branches. Pure olfactants refer to odors that solely stimulate the olfactory nerve without any impact on the trigeminal nerve. For instance, coffee is classified as a pure olfactant. These objects do not elicit trigeminal activation [3].

There is compelling evidence to suggest that olfactory training can effectively aid in the recovery of a lost sense of smell. Neuroregeneration is a significant aspect of olfaction, as the olfactory neurons are the sole neurons that undergo systematic regeneration in the adult mammalian brain. It remains to be determined whether the level of regeneration observed in other mammals is also present in the human olfactory system. The synapses located at the olfactory bulb exhibit an extreme level of convergence in the mammalian nervous system.

Figure 2. Loss and Regeneration of Smell [4].

References

3. Jacquot, L., J. Monnin, and G. Brand, Influence of nasal trigeminal stimuli on olfactory sensitivity. Comptes Rendus Biologies, 2004. 327(4): p. 305-311.

4. JIANG, K. How COVID-19 Causes Loss of Smell. 2020; Available from: https://hms.harvard.edu/news/how-covid-19-causes-loss-smell.

(04): 00:21:39 Brain Processing of Smell

Specifically, the pattern of synapsing between the olfactory epithelium and the olfactory bulb results in all receptors of a given subtype, which number around 350 in humans and 1200 in mice, converging to a single location in the bulb known as a glomerulus. In fact, there are two glomeruli, which are mirror images of each other. Therefore, all receptors of one subtype converge to two mirror glomeruli on the olfactory bulb. According to the textbook view, each receptor subtype is responsive to a small subset of different molecular shapes, also known as autotopes, which are the molecular aspects of deodorant. As a result, each receptor is responsive to a different subset of autotopes. Each autotope has the ability to activate a distinct subset of receptors, resulting in a vast array of potential combinations within the 350-dimensional space present in humans. As a result of this convergence, a map reflecting receptor identity is formed on the bulb. Subsequently, information is transmitted from the bulb to various targets in the brain, including the primary olfactory cortex and the Rhino cortex, which are located on the ventral surface of the brain in the lower portion of the temporal lobe. The information is then directly transmitted to the amygdala, hypothalamus, and cerebellum, as well as other areas of the brain [5].

Figure 3. Olfactory system Olfactory bulb, olfactory epithelium with olfactory receptor neurons [6].

References

5. Gaillard, I., S. Rouquier, and D. Giorgi, Olfactory receptors. Cellular and Molecular Life Sciences CMLS, 2004. 61(4): p. 456-469.

6. Rebholz, H., et al., Loss of Olfactory Function—Early Indicator for Covid-19, Other Viral Infections and Neurodegenerative Disorders. 2020. 11.

(05): 00:24:40 Smell & Memories

The durability of olfactory memory surpasses that of other perceptual experiences, suggesting a close association between olfaction and memory. Unlike sound waves, which traverse multiple pathways to reach the memory center, olfactory stimuli take a more direct route. been observed in various studies. Allusions to literature often include the commonly referenced "priest effect." This phenomenon occurs when an individual consumes a Madeleine and experiences an immediate recollection of the taste and scent from a childhood event where the same Madeleine was present. This occurrence is well-documented and has been the subject of extensive research [7].

Figure 4. Odor Linked Memory [7].

References

7. Thomas, A.-F. and M.H. Papesh. Why Are We so Scent-Imental? Studying Odor-Linked Memories. Available from: https://kids.frontiersin.org/articles/10.3389/frym.2022.667792.

(06): 00:29:07 Humans & Odor Tracking

The olfactory abilities of humans are noteworthy. To illustrate, mercaptans are incorporated into cooking gas to confer an odor, as the gas itself is odorless. It is important to note that the scent of gas is not that of propane, but rather an additive. The detection threshold, or the minimum concentration at which a scent can be detected, is 0.2 parts per billion. Currently, there is no machine, including gas chromatographs, that can effectively perform the task at hand. This lack of technology hinders the ability to concretely reproduce the desired outcome. The laboratory of Professor Noam Sobel is currently conducting research on the odorant estro tetra enol. The study participants have demonstrated the ability to detect this chemical at a concentration of 10 to the negative 12 molars in the liquid phase. To provide a tangible comparison, if one were to add one drop or 1ml of this chemical to one Olympic size swimming pool and compare it to another pool without the chemical, the difference in odor would be detectable by the human nose. This represents the threshold of detection for this particular odorant. Humans possess a remarkable olfactory detection ability, which is comparable to that of other mammals. Moreover, it is possible to enhance our olfactory perception.

In a recent study conducted by Professor Dr. Sobel, participants who were not affiliated with his graduate program were subjected to a complete sensory deprivation experience. This was achieved by blocking their eyes and ears, and having them wear heavy gloves to prevent any external stimuli. The researchers then created a consistent path in the grass by burying odor-impregnated twine underneath it. This allowed for a consistent odor trial to be generated for each participant. The buried object was discovered beneath the grass, and the researchers employed aerial photography, as well as a sensor pack is worn by participants, to measure nasal airflow in real-time and track behavior using rtk GPS. This technology involves laying a radio frequency grid over the GPS grid to achieve millimeter resolution in space, primarily used by surveyors. The findings revealed that individuals were able to perform the task immediately, and after four days of training, the speed at which they could crawl became the limiting factor. From a systems neuroscience perspective, these results were particularly intriguing. The presence of two nostrils plays a significant role in nasal function. In order to investigate this, a nasal prosthesis was developed with two variations: one that merged the two nostrils into a single, centralized opening, and another that maintained the two nostrils as separate entities. The performance of individuals was then compared under these two conditions. Results indicated that participants performed significantly better with two separate nostrils as opposed to a single, centralized nostril.

Figure 5. Odor Monitoring and Detection [8].

References

8. Odor Monitoring and Detection Tools. Available from: https://www.biocycle.net/odor-monitoring-and-detection-tools/.

(07): 00:39:25 The Alternating Nasal Cycle & Autonomic Nervous System

The nasal cycle (NC) is the naturally occurring congested and uncongested nasal mucosa that occurs throughout the day, with congested nasal mucosa on one side typically followed by uncongested nasal mucosa on the opposite side. In fact, if you were to repeatedly do that, you would discover that your high-flow nostrils and low-flow nostrils alternate on average every two and a half hours. The nasal cycle is when one nostril is blocked by pressing on it from the side while you sniff in, and the other is blocked while you sniff in. It turns out that this is related to the balance of the autonomic nervous system. The autonomic nervous system also had sympathetic and parasympathetic components, and they are in balance or imbalance in many diseases. We have this constant shift from side to side, and the shift becomes extremely pronounced in sleep, so we can measure the power of the difference. In sleep, we also have this phase shift of power where one closes and one opens completely. The switch from the left to the right nostril is caused by the interaction between the sympathetic and parasympathetic neural systems [9].

Additionally, Dr. Sobel's lab developed a wearable device called a nasal halter that is attached to a person's body and measures airflow in each nostril separately over the course of 24 hours. Based on the data collected from this measurement, the researchers at Dr. Sobel's lab can distinguish between Attention-Deficit / Hyperactivity Disorder or ADHD and non-ADHD and can also tell you whether an adult is taking Ritalin or not. Yoga practitioners who are serious about their practice are brought in by researchers to see if they can change their nasal cycles from left to right by will alone, rather than by tricking themselves. If they can, researchers will learn how to do it from them and use it to treat ADHD. 14 yoga instructors were tested by Dr. Sobel's lab on the condition of enrollment that they could control switching from the left to the right nostril without plugging a nostril. In this experiment, 0 of the 14 participants were successful.

Figure 6. Nasal Cycle [10].

References

9. Pendolino, A.L., B. Scarpa, and G. Ottaviano, Relationship Between Nasal Cycle, Nasal Symptoms and Nasal Cytology. Am J Rhinol Allergy, 2019. 33(6): p. 644-649.

10. Nasal Cycle And Its Impact On Mucociliary Clearance. Available from: https://www.docplexus.com/posts/nasal-cycle-and-its-impact-on-mucociliary-clearance.

(08): 00:48:18 Cognitive Processing & Breathing

The nasal cycle is not solely related to olfaction, but rather a distinct narrative regarding brain function. A proposed theory, known as the "sniffing brain approach," suggests that nasal inhalation plays a significant role in driving various aspects and patterns of neural activity and cognitive processing. This theory draws inspiration from olfaction, as the mammalian brain evolved from this sense and is dependent on sniffing for information. The processing of information is directly linked to nasal inhalation, as the brain has evolved to process information upon inhalation onset. This property has become meaningful in brain processing beyond olfactory information, extending to any type of information. Dr. Sobel conducted a study on visual-spatial processing, comparing the differences in performance between inhalation and exhalation. The results showed that the brain processes visual-spatial information differently during inhalation and exhalation. Specifically, participants performed significantly better on the visual-spatial task during inhalation. The task at hand involves the identification of shapes and their feasibility in the physical world. The objective is to discern whether a given shape is structurally sound or not, based on the observation of its facets. Some of the shapes presented in the task exhibit characteristics of impossible figures, where a facet fails to connect with another, thereby rendering them implausible in reality. It is a visual-spatial task that does not involve pure aesthetics. The researchers deliberately selected a non-ventral temporal task in the olfactory cortex domain. The participants exhibited superior performance during inhalation as compared to exhalation, and both nostrils were occluded while they were exposed to mouth breathing. In this specific task, participants exhibited superior performance in mouth inhalation compared to mouth exhalation. However, the disparity observed between nasal inhalation and exhalation was more significant than that of the former. Nasal breathing is significantly advantageous for one's overall health in comparison to oral breathing, and it also has a positive impact on cognitive function. The act of nasal breathing has been shown to influence cognitive processes. Numerous studies have indicated that nasal inhalation has the potential to regulate cognitive processing and its timing [11]. The olfactory sensory neuron is located at the superior aspect of the nasal cavity, commonly referred to as the nostrils. It is noteworthy that this is the sole location where the brain interfaces with the external environment, as opposed to the retina which is safeguarded by a lens. In this region, neurons are in direct contact with the surrounding milieu.

Figure 7. Breathing Affects Your Brain and Cognitive Processing [12].

References

11. Grassmann, M., et al., Respiratory Changes in Response to Cognitive Load: A Systematic Review. Neural Plast, 2016. 2016: p. 8146809.

12. Miller, G., How Does Breathing Affect Your Brain? 2022.

(09): 00:54:47 Neurodegenerative Diseases & Olfaction

The existence of neurons that are in direct contact with the external environment has given rise to various hypotheses concerning the possible mechanisms underlying neurodegeneration. The early onset of neurodegenerative diseases, such as Parkinson's disease, is commonly associated with the loss of olfactory function. Nevertheless, this particular symptom lacks specificity and is inadequate for diagnostic purposes. The loss of olfactory function is regarded as an initial indication of neurodegeneration. There exists a hypothesis, albeit not extensively acknowledged, that posits the possibility of Alzheimer's disease being caused by a pathogen that infiltrates the brain via the olfactory pathway. This underscores the notion that the olfactory system may function as a conduit to the central nervous system.

Dr Sobel lab also build devices that generate odors and we they call it olfactometer this instrument cost a quarter of million euro and its pathetic its slow, contaminated its nowhere near the resolution of your system, so one of the reason that not happened is just the utterly poor control of the stimulus, there are standard clinical tests of olfaction basically two that sort of control the world in this respect, the older one is a test called UPSIT “University of Pennsylvania smell identification test, it was developed by Richard Dodie Penn and it’s a test where you scratch and sniff and it’s a four alternative forced choice test with 40 odorants you have this 40 pages that you page through and you sniff and smell, and its been normed on Gazillions of tests, so there reduced UPSIT and Alzheimer and Parkinson and then a host of different diseases and also there is European version called sniffing sticks, that has the sort of concept of that one isn’t scratch and sniff it’s like the pens that you open up and sniff but they are not convenient as delivering stimuli and vision and audition.

Figure 8. Neurodegenerative Diseases & Olfaction [13].

References

13. Doty, R.L., Olfactory dysfunction in Parkinson's disease. Nature Reviews Neurology, 2012. 8(6): p. 329-339.

(10): 01:00:12 Congenital Anosmia

Congenital Anosmia is a medical condition characterized by the absence of the olfactory sense from birth. It is estimated that this condition affects approximately 0.5% of the population, which is a significant proportion. However, the accuracy of this estimate remains uncertain. Interestingly, the diagnosis of congenital anosmia typically occurs at the age of 14, which is a noteworthy fact. The diagnosis of congenital anosmia is typically made at an average age of 14 years, indicating that some individuals may receive a diagnosis even later. This condition can lead to social difficulties and is associated with a range of negative life events. Additionally, individuals with anosmia experience a decreased lifespan, as they tend to pass away at a younger age. Other symptoms may include a reduction in social and romantic contact. The burning sensation in the nose and nostrils is a common occurrence, although it is unclear whether individuals possess an olfactory bulb. In adulthood, most individuals do not have an olfactory bulb, or they may have remnants of a shriveled olfactory bulb. The cause and effect of these symptoms are unknown. Kalman syndrome, a condition characterized by hypogonadism development in men, is directly linked to anosmia. All individuals with Kalman syndrome are anosmic, but not all congenital anosmic individuals have Kalman syndrome. Therefore, it can be concluded that Kalman syndrome is associated with anosmia. The sense of smell and reproductive processes are frequently associated and exhibit a strong correlation across all mammalian species, including humans, who are classified as large terrestrial mammals [14].

Figure 9. Congenital Anosmia [15].

References

14. Congenital anosmia. Available from: https://rarediseases.info.nih.gov/diseases/9486/congenital-anosmia.

15. Umesh, V., K. Nader, and O. Salah, A case of congenital anosmia. Neurology, 2016. 87(22): p. 2384.

(11): 01:06:19 Handshaking, Sharing Chemicals & Social Sensing

Humans possess the ability to consciously or subconsciously encode the identification of individuals with whom they interact, based on their olfactory or other chemical cues. This process occurs continuously, with the majority of it being subconscious. Human behavior is often scrutinized through the lens of olfaction, as well as visual observation. In contrast, dogs overtly engage in olfactory-based interactions, as evidenced by their tendency to sniff each other upon initial contact. Humans, however, do not typically approach strangers and engage in such olfactory-based interactions. There is a social expectation to engage in olfactory interactions with our infants, which is not considered culturally taboo. This practice is widely accepted and deemed appropriate, whereas the act of sniffing unfamiliar individuals is not commonly observed. Handshaking is a peculiar behavior that is not exclusive to the Western world, contrary to popular belief. It is prevalent in various cultures, and its origins remain poorly understood. The evolution of this behavior is a subject of inquiry that requires further investigation.

Human behavior includes social chemo-signaling, although it is unclear how chemo-signaling moves from one person to another. Humans shake hands to greet one another, however, it is unknown what functions these handshakes provide. Researchers discreetly videotaped 271 people during a structured welcome event with or without a handshake to investigate whether handshakes are utilized to sample conspecific social chemosignals. Humans frequently and selectively increase this activity after a handshake, according to our research. Subjects increased sniffing of their own right shaking hand by more than 100% following handshakes among members of the same gender. On the other hand, following handshakes, individuals of both sexes increased sniffing of their own left hand that wasn't being shaken by more than 100%. The effects were drastically changed when participants were exposed to undetected smells, demonstrating the effects' olfactory origin. Handshakes may therefore function as active but covert social chemo-signaling, which probably has a significant impact on daily human behavior [16].

References

16. Frumin, I., et al., A social chemosignaling function for human handshaking. eLife, 2015. 4: p. e05154.

(12): 01:15:07 Smelling Ourselves & Smelling Others

Various theoretical frameworks have suggested that individuals are attracted to each other due to similarities in their bodily scents. In order to examine this phenomenon, a cohort of individuals with comparable olfactory profiles was enlisted as study participants, originating from diverse regions across Israel. Scholars have identified dyads of individuals who maintain a platonic, homosocial bond. These friendships are established between individuals of opposite genders who possess a shared and delicate bond, which is founded on a mutual "click" or connection. The investigators obtained bodily scent specimens from subjects subsequent to a twenty-one-day interval of utilizing unscented shampoo and soap, succeeded by two evenings of solitary rest while wearing a T-shirt. The researchers employed a method to extract body odor and investigated whether individuals who were considered close friends exhibited greater similarity in body odor than would be expected by chance. The researchers employed an electronic olfactory system, comprising sensors that exhibit a reaction to molecules present in the air, to collect samples of human body odor. The present device is designed to mimic the operational mechanism of the nasal cavity in mammals. The research findings indicate that there is a positive correlation between social compatibility and similarity in body odor among individuals, exceeding the level that would be expected by chance. Individuals who possess a greater degree of olfactory similarity are more inclined to perceive one another as amicable and are more likely to form social bonds. As a result, researchers have developed a means of utilizing electronic olfaction to predict the likelihood of interpersonal relationships. Humans engage in the olfactory perception of themselves and others on a daily basis [17].

Figure 10. Smelling Ourselves & Smelling Others [18].

References

17. Perl, O., et al., Are humans constantly but subconsciously smelling themselves? 2020. 375(1800): p. 20190372.

18. AHMED, I. Friends at first sniff: People drawn to others who smell like them. 2022; Available from: https://phys.org/news/2022-06-friends-people-drawn.html.

(13): 01:22:02 Odors & Romantic Attraction

A study has made a distinctive addition to the existing literature on the role of body odors (BOs) in romantic relationships. The findings reveal that irrespective of the nature or disagreeableness of BOs, individuals who have undergone a separation tend to exhibit a stronger commitment to their relationship when they have a higher level of familiarity and positive response towards their partner's BOs. The study found that a negative correlation exists between relationship commitment and the hedonic evaluation of a partner's body odor, indicating that individuals with lower relationship commitment are more likely to consider breaking up with their partner due to the unpleasantness of their body odor. In addition, it has been observed that increased exposure to a partner's body odors is positively correlated with enhanced hedonic evaluations of said odors. This finding is consistent with previous research that has established a significant association between these variables. The possibility exists that a rise in the frequency of exposure to one's partner's body odors is motivated by a hedonic fondness for these odors, which may establish a form of positive feedback loop that could potentially enhance commitment to the relationship [19].

Several studies propose that the perception of body odor plays a moderating role in the selection of a mate, serves as a means of solace in established relationships, and could potentially indicate the deterioration of a relationship through processes of disgust. Regarding olfactory capacity, possessing a strong sense of smell may aid in the identification of a suitable partner, augment sexual encounters, promote relationship stability, and ensure empathic responsiveness, all of which are predictors of the durability of a relationship. Thus, the sense of smell, or olfaction, assumes a significant, albeit insufficiently investigated, function in the context of romantic partnerships [20].

References

19. Keaveny, M. and M.K. Mahmut, Love Stinks: The Association between Body Odors and Romantic Relationship Commitment. Brain Sci, 2021. 11(11).

20. Mahmut, M.K. and I. Croy, The role of body odors and olfactory ability in the initiation, maintenance and breakdown of romantic relationships – A review. Physiology & Behavior, 2019. 207: p. 179-184.

(14): 01:24:58 Vomeronasal Organ, “Bruce Effect” & Miscarriage

The reproductive behavior of terrestrial mammals is primarily influenced by olfactory cues, with the main olfactory system (cranial nerve I) and trigeminal nerve (cranial nerve V) serving as the primary subsystems for odor transduction. Additionally, many terrestrial mammals possess a secondary olfactory system, which includes the vomeronasal organ located within the nasal passage. This organ contains specialized vomeronasal receptors and may connect to the roof of the mouth in some species. The phenomenon under consideration is associated with a distinct segment of the olfactory bulb, which is not synonymous with the primary olfactory bulb. This particular segment is commonly known as the accessory olfactory bulb, and it is directly connected to the limbic system, which governs both reproductive and aggressive behaviors. In the majority of land-dwelling mammals, this subsystem is responsible for processing olfactory stimuli, which are occasionally referred to as pheromones. Odorants, commonly known as pheromones, are emitted by individuals of a species to influence the behavior or hormonal state of another member of the same species. These pheromonal effects can be remarkably evident through their odor [21].

The Bruce effect, first observed by British scientist Margaret Bruce in 1959, pertains to the phenomenon wherein a pregnant mouse exposed to a non-stud male during an early critical stage of pregnancy is likely to miscarry or abort the pregnancy. The decision made by the female in question can be deemed irrational as she had invested significant biological resources in conceiving and carrying the pregnancy to term, only to terminate it due to a perceived odor. It is noteworthy that this effect appears to be highly resilient. The Bruce effect can be induced by the mere presence of the odor of a non-stud male, which is estimated to occur in approximately 80% of exposures. It is not necessary to physically introduce the male, as the odor alone is sufficient. If the Vomeronasal organ is ablated in female mice, the resulting impact is contingent solely upon the presence of the Vomeronasal organ, as the ablation involves the destruction of the small nasal structure and the effects subsequently dissipate.

Despite the presence of an anatomical structure resembling the Vomeronasal organ in humans, it is widely accepted that this organ is vestigial and non-functional. The Vomeronasal organ also referred to as the Jacobson organ, is not considered to be operational in humans. The olfactory system's sensory organ is commonly believed to be the Jacobson organ in humans, which is thought to be vestigial and non-functional. However, the main olfactory system mediates various pheromonal effects, including social chemo signaling. The determination regarding the functionality of the Vomeronasal organ is based on approximately one and a half scholarly articles. As per Dr. Sobel's findings, it is plausible that humans may undergo a phenomenon akin to the Bruce effect. This could manifest in the form of a significant incidence of spontaneous miscarriages during the initial trimester of pregnancy. A significant proportion of human pregnancies result in miscarriage, and among them, a subset remains unexplained. It is hypothesized that a statistical or environmental factor, akin to the remnant Bruce effect, may be at play in humans. The occurrence of consecutive unexplained miscarriages is considered adequate for the diagnosis of unexplained pregnancy loss. In some cases, couples have reported experiencing up to twelve pregnancy losses without any discernible reasons. Researchers have postulated that a phenomenon similar to the Bruce effect may be responsible for these miscarriages, although it is not identical to the mechanism observed in mice [22].

Figure 11. Bruce Effect [23].

References

21. D'Aniello, B., et al., The Vomeronasal Organ: A Neglected Organ. 2017. 11.

22. Eccard, J.A., M. Dammhahn, and H. Ylönen, The Bruce effect revisited: is pregnancy termination in female rodents an adaptation to ensure breeding success after male turnover in low densities? Oecologia, 2017. 185(1): p. 81-94.

23. Ichikawa, M.J.Z.s., Synaptic mechanisms underlying pheromonal memory in vomeronasal system. 2003. 20(6): p. 687-695.

(15): 01:40:20 Social Chemo-Signals, Fear

Social chemical signals pertain to diverse forms of stimuli that are exchanged among conspecifics and are perceived through chemical senses like olfaction, vomer olfaction, taste, and tarsal chemoreception. Endogenous compounds resulting from physiological processes and socially acquired cues, in conjunction with specialized chemical messengers referred to as pheromones, which have been evolutionarily favored for the purpose of communication, are accountable for conveying these signals. It is crucial to recognize that although all social chemo signals fall under the category of pheromones, not all social chemo signals can be categorized as such. The ambiguity in the definition of pheromones has led to the erroneous use of the term to describe any form of odor-based communication without discrimination.

It has been established that humans emit chemical signals from their bodies that have an impact on the behavior of others. Among these signals, the scent of fear has been extensively researched. It is a fact that humans and other mammals release a distinct body odor when experiencing fear. This phenomenon was initially observed in humans by Denise Chain. The emitted body odor in humans has been shown to increase the autonomic arousal and sympathetic state of others, and the scent of fear is known to be contagious. Additionally, dogs have been found to be capable of detecting the odor of fear in humans, and humans have been shown to possess the same ability. According to certain laboratory data, it has been observed that individuals are capable of distinguishing between body odors collected from individuals experiencing fear and those collected from the same individuals in a non-fearful state [24].

Figure 12. Human chemosignals [25].

References

24. Schaal, B., Social Chemosignal, in Encyclopedia of Neuroscience, M.D. Binder, N. Hirokawa, and U. Windhorst, Editors. 2009, Springer Berlin Heidelberg: Berlin, Heidelberg. p. 3756-3759.

25. Zheng, Y., et al., Human chemosignals of disgust facilitate food judgment. Scientific Reports, 2018. 8(1): p. 17006.

(16): 01:50:26 Chemo-Signaling, Aggression & Offspring

Eva Mishor, a researcher at Dr. Soblel's laboratory, conducted a study on the olfactory cues associated with aggressive behavior. Specifically, Mishor investigated the chemo-signaling mechanisms underlying aggression by collecting body odors from mixed martial arts (MMA) clubs. The role of body volatiles in the facilitation or suppression of conspecific aggression in land-dwelling mammals has been noted as a noteworthy aspect. The objective of the research was to examine the effects of hexadecanal (HEX), a volatile organic compound that is present in the human body and has been linked to mammalian-wide social chemo signals, on human aggression. A noteworthy dissociation was observed through the utilization of validated behavioral paradigms. The study discovered that HEX, a particular chemical compound, has the ability to inhibit aggressive behavior in males, but has the opposite effect on females, as determined by their olfactory perception. Following this, a pattern of brain activity that corresponds to behavior was disclosed by means of functional brain imaging. The research findings indicate that the administration of HEX resulted in increased neural activity in the left angular gyrus, a brain region that is linked to the identification of social cues, among male and female subjects. According to the research, the utilization of HEX, along with modulated functional connectivity, demonstrated a significant influence on the angular gyrus and a neural network that is linked to social evaluation (temporal pole) and aggressive behavior (amygdala and orbitofrontal cortex). The findings were in line with behavior and demonstrated that connectivity exhibited an increase in males but a decrease in females, suggesting a sex-specific impact. The statement above posits that the social chemo signaling that is specific to sex is a critical factor in the fundamental mechanisms that drive human aggressive behavior [26].

If an individual is a biological descendant and possesses a molecule that induces heightened aggression in their mother and reduced aggression in their father, it can be considered advantageous for the individual. A research article authored by a Japanese group has been recently published, wherein they have investigated the odors emanating from the head of infants. The researchers employed Gas Chromatography-Mass Spectrometry (GCMS) to quantify the volatile compounds present in the head of infants. The study was conducted due to the cultural significance of the baby head across various cultures, including Japan. The results of the study revealed that hexadecanal was the most abundant semi-volatile compound released from the head of infants. Infants appear to have a mitigating effect on paternal or male parental aggression, while simultaneously eliciting an increase in maternal or female parental aggression in their presence.

References

26. Mishor, E., et al., Sniffing the human body volatile hexadecanal blocks aggression in men but triggers aggression in women. 2021. 7(47): p. eabg1530.

(17): 02:03:57 Menstrual Cycle Synchronization

Martha K. McClintock's paper titled "Menstrual Synchrony and Suppression" delves into the phenomenon of menstrual synchrony and its potential implications. The research comprised of 135 female college students residing in a dormitory, and the findings indicated that social interaction may exert a potent influence on the menstrual cycle. According to McClintock's research, there is evidence to suggest that the menstrual cycles of women who cohabitate tend to synchronize gradually. The aforementioned statement implies that social factors exert a noteworthy influence on the regulation of the menstrual cycle. The author postulates that the synchronization of menstrual cycles could be attributed to the exchange of pheromones or other social and environmental factors. However, further investigation is required to comprehensively comprehend the underlying mechanisms of this phenomenon. The author explores the potential ramifications of menstrual synchrony, including the hypothesis that it may have evolved as a mechanism to enhance the likelihood of conception within a community. The aforementioned proposition posits that the synchronization of menstrual cycles may confer advantageous traits and is not solely a consequence of social engagement.

In general, McClintock's research illuminates a fascinating and inadequately comprehended occurrence in the field of human biology. The results indicate that social variables exert a noteworthy influence on the regulation of the menstrual cycle and that the synchronization of menstrual cycles may have developed as a mechanism to enhance the likelihood of conception among members of a group. Further investigation is required to comprehensively comprehend the mechanisms underlying menstrual synchrony and its prospective implications. Conclusively, McClintock's scholarly article offers significant perspectives on the intricate correlation between social determinants and the regulation of the menstrual cycle. The investigation delves into the phenomenon of menstrual synchrony, thereby illuminating a fascinating and inadequately comprehended facet of human biology. Further investigation is required to comprehensively comprehend the mechanisms underlying menstrual synchrony. However, the results indicate that social interaction can exert a potent impact on the menstrual cycle and that menstrual synchrony may confer adaptive advantages [27].

Figure 13. Menstrual Cycle [28].

References

27. McClintock, M.K., Menstrual Synchrony and Suppression. Nature, 1971. 229(5282): p. 244-245.

28. The Science Behind Period Syncing. Available from: https://www.forbes.com/sites/alicebroster/2020/08/07/the-science-behind-period-syncing/?sh=6559e1c43471.

(18): 02:12:11 Sweat, Tears, Emotions & Testosterone

A hypothesis posits that emotional tears in humans may possess a chemo-signaling function akin to that observed in mice. The study involved the collection of negative-emotion-related tears from female participants, which were then presented to male participants for olfactory stimulation. The results indicated that exposure to these tears led to a reduction in sexual arousal and testosterone levels among the male participants. The research posits that chemo signals present in human emotional tears may have an impact on the behavior and physiology of other individuals, thereby prompting inquiries into the evolutionary and functional aspects of emotional tearing in humans. The study concludes by advocating for additional research to clarify the chemical composition of tears that are shed due to emotional stimuli and their potential physiological and psychological functions. The present study offers empirical support for a plausible role of human emotional tears that extends beyond their conventional function of safeguarding the eye, an aspect of research that has received comparatively less attention. The results present novel opportunities for exploring the mechanisms and development of affective expression in human beings, and could potentially bear relevance to domains such as psychology, anthropology, and biology [29].

The research delves into the evolutionary and cultural implications of emotional tears among the human species. Furthermore, the argument posits that the act of shedding tears as a result of emotional stimuli is a behavior that is both universal and exclusive to the human species. Additionally, recent advancements in theoretical frameworks and empirical investigations pertaining to this subject matter are succinctly summarized. The authors propose that utilizing an evolutionary perspective provides a robust foundation for examining the roles of tears, specifically in relation to the crying behavior of infants, as discussed in the initial section of the manuscript. Scholars also examine the cultural importance of tears, encompassing their utilization in communal and spiritual ceremonies. In general, the research presents a thorough examination of the present comprehension of human emotional tears, taking into account both evolutionary and cultural viewpoints [30].

In a study conducted by Dr. Sobel, participants' tears were collected and analyzed. The results indicated that tears are devoid of any discernible odor. Upon exposure to tears, a significant reduction in testosterone levels was observed within a timeframe of approximately 20-30 minutes. Additionally, a 14% decrease in free testosterone levels was noted. Furthermore, tears were found to have a pronounced effect on reducing brain activity in both the hypothalamus and gyrus. The act of sniffing tears has been found to have a calming effect on male individuals, resulting in a decrease in aggressive behavior.

References

29. Gelstein, S., et al., Human Tears Contain a Chemosignal. 2011. 331(6014): p. 226-230.

30. Gračanin, A., L.M. Bylsma, and A.J.J.M. Vingerhoets, Why Only Humans Shed Emotional Tears. Human Nature, 2018. 29(2): p. 104-133.

(19): 02:27:46 Science Politics

The volume of tears in humans has been observed to increase in response to emotional arousal. As far as the existing literature is concerned, there is a dearth of research that has explored the correlation between emotional arousal and tear volume in the animal kingdom. The Schirmer tear test (STT) was conducted to evaluate tear volume in dogs prior to and subsequent to reunions with their owners and familiar non-owners. The lacrimal secretion volume exhibited a notable increase upon reuniting with the proprietor was as opposed to a familiar non-proprietor. The application of an oxytocin solution to the eyes of dogs resulted in an increase in tear volume. This finding suggests that oxytocin may play a role in regulating tear secretion during reunions between dogs and their owners. Ultimately, the study involved soliciting human participants to evaluate their impressions of photographs depicting dogs, both with and without the application of artificial tears. The results indicated that the photographs featuring artificial tears were associated with more favorable ratings from participants. The findings indicate that tears induced by emotions may enhance the emotional bonding between humans and dogs [31].

References

31. Murata, K., et al., Increase of tear volume in dogs after reunion with owners is mediated by oxytocin. Current Biology, 2022. 32(16): p. R869-R870.

(20): 02:37:54 Food Odors & Nutritional Value

The sensory modalities of taste and smell are crucial factors in the processes of dietary choice and metabolism. The impact of sensory function on customary food consumption and consequent health status necessitates consideration of various other factors, including but not limited to environment, exposure, and culture. Therefore, it is imperative to customize the dietary approach for individuals with chemosensory issues [32].

A recent investigation has examined the impact of food odor exposure on the appetite, nutritional intake, and body weight of elderly individuals with dementia residing in nursing homes in the Netherlands. This research constitutes a trial that is non-randomized and non-blinded, with a single arm, and a sample size of 17 individuals diagnosed with dementia. Over the course of five consecutive days during lunchtime, the participants were subjected to the scent of hot meals. The findings indicate that exposure to food odor had a significant impact on the participants' appetite, nutritional intake, and body weight. According to the authors, exposure to food odor may present a viable intervention to enhance the nutritional status of elderly individuals with dementia who exhibit reduced appetite and nutritional consumption. Nevertheless, the study is subject to certain limitations such as the restricted sample size and the absence of a control group. Therefore, additional research is required to validate the results [33].

The olfactory system plays a significant role in the detection and interpretation of food aromas and volatile flavors. Instances highlighting the significance of olfactory perceptions can be observed in scholarly works concerning product quality anomalies, as well as in the crucial role played by aroma and flavor attributes in influencing the degree of consumer approval towards food items. Evaluating the olfactory-mediated attributes of flavors poses a considerable challenge due to various factors. The existence of specific anosmia suggests the presence of significant individual variations in olfactory acuity. The judgment of samples by panelists is frequently impacted by the immediate context in which the evaluation takes place. The task of establishing a practical and widely accepted terminology for characterizing odors in sensory evaluations can pose a challenge. Despite the obstacles, the olfactory abilities of humans remain unparalleled in discerning the quality of food aroma and flavor, rendering instrumental analyses an inadequate alternative. The identification of chemical constituents of food flavors is insufficient without cross-referencing them against human sensitivities to estimate their sensory impact [34].

Figure 14. Chemosensitivity of the Olfactory System [35].

References

32. Kershaw, J.C. and R.D. Mattes, Nutrition and taste and smell dysfunction. World J Otorhinolaryngol Head Neck Surg, 2018. 4(1): p. 3-10.

33. Verwijs, M.H., et al., The Effect of Food Odor Exposure on Appetite and Nutritional Intake of Older Adults with Dementia. The journal of Nutrition, health & Aging, 2022. 26(2): p. 112-118.

34. LAWLESS, H., THE SENSE OF SMELL IN FOOD QUALITY AND SENSORY EVALUATION. 1991. 14(1): p. 33-60.

35. Julliard, A.-K., et al., Nutrient Sensing: Another Chemosensitivity of the Olfactory System. 2017. 8.

(21): 02:45:34 Human Perception & Odorant Similarity

Humans are incredibly similar to one another in their olfactory perception and this is in contrast to what most people think, the misconception is there for two reasons, first of all, we are attracted by outliers, olfactory pleasantness is highly correlated amongst humans and let's put this in the number you’ll take a bunch of humans and a bunch of odorants and have to write pleasantness the correlation across the human would be about 0.8 that’s incredibly high. A research study [36] investigated the correlation between odorant receptor responses and odorant perception among the participants. The investigation scrutinized the 50 most prominent OR/odorant phenotype pairings and evaluated linkage disequilibrium at each genetic locus to establish the correlation between linked and associated ORs and the perception of odorants. A subsequent scholarly publication [37] conducted an experiment to assess the feasibility of utilizing human odorant receptor responses from heterologous assays as a means of simulating human odor perception. The study also constructed models that integrated both methods. The study developed machine learning algorithms for the purpose of forecasting ligand molecules that bind to 34 distinct human olfactory receptors (ORs). Another study presented a concise overview of the process of odor perception in human beings, which is triggered by the stimulation of odorant receptors located in the nasal cavity. The specific odds ratios associated with distinct olfactory percepts remain unknown, in contrast to vision and taste, where receptors are associated with the perception of diverse colors and tastes. The existing studies and articles indicate that there is a significant knowledge gap regarding human perception and odorant similarity. To comprehend the correlation between odorant receptor responses and odorant perception in humans, further research is imperative [37].

Figure 15. Human Olfactory Perception [37].

References

36. Trimmer, C., et al., Genetic variation across the human olfactory receptor repertoire alters odor perception. 2019. 116(19): p. 9475-9480.

37. Kowalewski, J. and A. Ray, Predicting Human Olfactory Perception from Activities of Odorant Receptors. iScience, 2020. 23(8): p. 101361.

(22): 02:52:12 Digitizing Smell, COVID-19 & Smell

Current endeavors involve the digitization of olfactory perception through the utilization of molecular cartography and artificial intelligence methodologies. Osmo.ai is a nascent enterprise that endeavors to enhance the physical and mental welfare of individuals by conferring olfactory capabilities upon computers [38]. The corporation aims to accomplish this objective through the integration of hardware, software, data, and financial resources to address the technical complexities associated with the digitization of olfactory stimuli [39]. The process of digitizing smells entails the systematic organization or anticipation of the specific molecules that are responsible for generating distinct olfactory perceptions. The utilization of sensory maps, akin to the ones employed in color vision, may aid in resolving this issue [40]. The concept of digitizing odors is currently in its nascent phase, however, it holds immense potential to bring about a paradigm shift in diverse domains such as healthcare and entertainment. This is due to the fact that it enables computers to scrutinize and recognize fragrances in manners that were hitherto unattainable.

An investigation into the viability of utilizing olfactory perception as a means of detecting COVID-19 infection. The research conducted an empirical investigation involving a sample size of some participants during the period spanning from March 25th, 2020 to September 23rd, 2020. The study aimed to construct a perceptual gauge of olfaction that could potentially serve as a screening tool. The research has demonstrated that the olfactory perception examination can serve as a suitable method for screening, which obviates the need for the transportation, distribution, and collection of tangible samples. The proposition put forth by the authors posits that olfactory perception has the potential to serve as a viable strategy in mitigating the spread of the COVID-19 outbreak. In summary, the research underscores the possibility of utilizing olfactory perception as a cost-effective and non-invasive method for conducting COVID-19 screening on a large scale [41].

Dr. Sobel's laboratory has recently published a paper detailing an algorithmic framework that can predict the perceptual similarity between any two molecular mixtures with a high degree of accuracy. The researchers in the lab have demonstrated the ability to both predict and design these mixtures. Additionally, the team has generated olfactory metameres, which are molecularly non-overlapping mixtures that produce identical smells. This is a significant advancement; as traditional perfumers would not believe it possible to generate two mixtures with no shared molecules that produce the same scent. The researchers utilized a map of 4,000 molecules, each with a known perceived smell, to create mixtures by projecting them onto the map and measuring their pairwise distance from all points. If a mixture falls on the lemon point, for example, it will produce a lemon scent, and if it falls on the tomato point, it will produce a tomato scent.

Figure 16. Digitizing Smell [42].

References

38. Giving computers a sense of smell to improve the health & well-being of human life.; Available from: https://osmo.ai/.

39. MULLIN, E. This Startup Is Using AI to Unearth New Smells. 2023; Available from: https://www.wired.com/story/this-startup-is-using-ai-to-unearth-new-smells/.

40. Richard C. Gerkin, a.A.B.W. Digitizing Smell: Using Molecular Maps to Understand Odor. Available from: https://ai.googleblog.com/2022/09/digitizing-smell-using-molecular-maps.html.

41. Snitz, K., et al., An olfactory self-test effectively screens for COVID-19. Communications Medicine, 2022. 2(1): p. 34.

42. Will Smell Ever Come to Smartphones?; Available from: https://www.newyorker.com/tech/annals-of-technology/is-digital-smell-doomed.

(23): 03:05:50 Medical Diagnostic Future & Olfaction Digitization

Distinctive odors are associated with individual diseases as a result of their unique metabolic processes. The aforementioned metabolic process produces metabolites that are linked to a distinct aroma. Upon undergoing digitization and achieving high resolution, the sense of olfaction is capable of detecting these scents. It is anticipated that the implementation of olfaction digitization at a level of visual and auditory resolution comparable to 4k will be employed in medical diagnosis. Moreover, it is expected that electronic olfactory systems will be widely adopted in residential lavatories.

Digital olfaction, or olfaction digitization, pertains to the encoding and communication of fragrances via electronic means. The operational principle of this technology involves the utilization of electronic noses and olfactometers to detect and categorize diverse scents [43]. Aromyx, a California-based enterprise, employs human olfactory and gustatory receptors to detect diverse aromas. Subsequently, the digital signatures are deciphered via machine learning and expressed in human terminology, including but not limited to woody, floral, fragrant, and smoky. The forthcoming 8th World Congress of Digital Olfaction Society, slated for December 7-8, 2023 in Tokyo, Japan, is poised to showcase emerging challenges in the realm of digital olfaction [44]. The ongoing advancement of this technology holds the promise of transforming multiple domains, including but not limited to the food and beverage sector, the fragrance industry, and medical diagnostics. Researchers are currently investigating the potential of olfactory sensors for the purpose of diagnosing diseases such as cancer, Parkinson's, and Alzheimer's, due to the presence of distinct olfactory signatures associated with these conditions [45].

References

43. Digital scent technology. Available from: https://en.wikipedia.org/wiki/Digital_scent_technology.

44. Digital Olfaction Society Meeting 2023: New Challenges. Available from: https://digital-olfaction.com/.

45. Business Scents: The Rise of Digital Olfaction. Available from: https://sloanreview.mit.edu/article/business-scents-the-rise-of-digital-olfaction/.

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