Published May 2023 on YouTube

Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior | Huberman Lab Podcast

1. Dr. Noam Sobel

Dr. Noam Sobel discusses the incredible power of human olfaction and chemosensation, including the ability to follow scent trails and how we process information about others based on their chemical signals. You'll learn about the impact of tears on hormone levels and the alternation of ease in breathing through each nostril. By the end of the episode, you'll never look at or smell the world around you the same way again.+

2. Science and Health

Andrew shares insights on the biology of the visual system and how Roka eyeglasses and sunglasses are designed to provide crystal clarity. He also talks about Thesis' customized nootropics and how they can enhance focus, clarity, and creativity. Lastly, he discusses Helix Sleep's customized mattresses and pillows that allow you to get the best possible night's sleep.+

3. Olfaction Circuits (Smell)

The Science of Smell:Noam Sobel discusses the primary and retronasal olfaction, the process of sniffing, and the interaction of airborne molecules with receptors in the nose. He also touches on the contribution of olfaction to food and taste.+
Olfactory Receptors:Noam shares insights on the olfactory system, including the number of receptors in the human nose and the amusing story of the origin of the myth of bloodhounds having a billion receptors.+
Olfactory Nerve Trauma:Noam and Andrew discuss how trauma to the back of the head can cause a Contracu injury, severing the olfactory nerve and resulting in the loss of the sense of smell. They also shed light on how much of what is in textbooks, scientific and medical, is absolutely wrong.+

4. Olfactory Insights

Olfactory Regeneration:Andrew and Noam discuss the ability of olfactory sensory neurons to regenerate in adult humans, as well as the time frame for recovery after injury or viral loss. They also mention alpha lipoic acid as a potential remedy for accelerating recovery of smell.+
Smelling and the Trigeminal Nerve:Noam and Andrew discuss the science behind smelling and how it involves more than just the olfactory system. They also touch on olfactory training and the importance of keeping neurons active to maintain their connections.+
Olfactory Regeneration:Noam and Andrew discuss the use it or lose it system of olfaction and the success of olfactory training programs. They also touch on the debated question of neuro regeneration in the human olfactory system compared to other mammals.+

5. Brain Processing of Smell

Noam explains the textbook view of how the olfactory bulb works, with each receptor subtype converging to one location in the bulb called a glomerulus. This creates a map reflecting receptor identity, which theoretically allows for the identification of different odors. Information then projects widely from the bulb to various targets in the brain.+

6. Smell & Memories

Andrew and Noam discuss the connection between smell and memory, and the unique pathway that olfaction takes to reach the hippocampus. They explore the idea that olfactory memories are formed more easily and maintained longer than other types of memories, especially when it comes to the first time we experience a smell.+

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Andrew discusses the importance of gut health and how Athletic Greens provides optimal and vital probiotics, adaptogens, vitamins, and minerals to meet all of his foundational nutritional needs. Listeners can try Athletic Greens and receive five free travel packs and a year's supply of vitamin D, three K two by visiting Huberman.+

8. Humans & Odor Tracking

Smell Training:Noam explains that humans have a remarkable sense of smell and discusses a study where people were trained to follow an odor trail with their nose. He also mentions the possibility of improving our sense of smell through training.+
Incredible Olfactory Abilities:Noam and Andrew discuss the incredible abilities of the human sense of smell, including the detection of odor at incredibly low concentrations and the ability to track odors like a dog. They share a story of a lab bet that led to an experiment showing that humans can track odors effectively.+
Odor Tracking:Noam and Andrew discuss a study where participants were completely deprived of sensory input and had to track a consistent odor path in the grass. They found that people could track the odor path right off the bat and that within an average of four days, the rate limiting factor became the speed at which they could crawl. They also constructed a nasal thesis to see if having two nostrils contributes to odor tracking and found that people performed better with two nostrils over one centralized nostril.+

9. The Nasal Cycle

The Nasal Cycle:Noam explains the nasal cycle, a constant shift from side to side that becomes pronounced in sleep. This cycle is linked to balance in the autonomic nervous system, which drives the switch from left to right nostril.+
Nasal Halter:Noam and Andrew discuss the nasal halter, a wearable device that measures airflow in each nostril separately and logs it for 24 hours, as a marker for balance in the autonomic nervous system and its potential use as a disease marker. The device can differentiate between ADHD and non-ADHD adults and determine if the adults are on Ritalin or not.+
Yoga and Nasal Cycles:Noam and Andrew discuss the world of yoga and its claims of controlling the nasal cycle. They share their study of 14 yoga teachers who claimed to be able to shift their nasal cycle from left to right by will alone, but none of them succeeded. The discussion also touches on the relationship between autonomic arousal and the shift in the nasal cycle.+

10. Cognitive Processing & Breathing

Nasal Cycle and Brain Function:Noam Sobel discusses the nasal cycle and its impact on brain processing. The sniffing brain approach theory suggests that nasal inhalation drives neural activity and cognitive processing, not just olfactory information. The study led by Offer Peril from their lab looked at something completely non-olfactory to support this theory.+
Nasal Breathing Benefits:Noam and Andrew discuss a study on visual spatial processing and the benefits of nasal breathing on cognition. Nasal inhalation is found to modulate cognitive processing, and it is good for dental health and overall health.+

11. Olfactory Loss and Digitizing Olfaction

Olfactory Loss:Noam explains how olfactory loss is an early sign of neurodegeneration and how Alzheimer's may enter the brain through the olfactory system. Andrew suggests having an olfactory task to track potential neurodegeneration, which is non-invasive and relatively pleasant.+
Digitizing Olfaction:Noam explains why olfaction has not been effectively digitized yet, unlike vision and audition, due to poor stimulus control and the lack of convenient tests.+

12. Congenital Anosmia

The Hidden Consequences:Noam and Andrew discuss the consequences of congenital anosmia, a condition where people are born without the sense of smell. Most people don't realize they have it until they're 14 years old, and suffer socially and have a shorter lifespan.+
Olfaction and Reproduction:Andrew and Noam discuss the direct link between olfaction and reproduction, specifically in the case of Kalman's syndrome, where hypogonadic development in men leads to anosmia. They highlight the tight link between olfaction and reproduction in all mammals, including humans.+

13. Sponsor: InsideTracker

Andrew discusses the importance of getting regular blood work done and introduces Inside Tracker, a personalized nutrition platform that uses data from your blood and DNA to help you understand your body and reach your health goals. He explains how Inside Tracker's personalized dashboard can help you address nutrition-based, behavior-based, and supplement-based approaches to move your values into optimal ranges.+

14. Smell and Behavior

Smell and Memory:Andrew shares a childhood story about how he was able to identify his friends' clothes by their smell. This raises the question of whether we subconsciously code identification of people we interact with based on their smell or other aspects of their chemistry.+
Unconscious Human Behavior:Noam discusses how humans engage in subconscious processing and how it affects our behavior. He also talks about the odd behavior of handshaking and how it is prevalent across cultures.+
Touching Behaviors:Noam and Dan conducted a study on how much people touch their face while waiting for an experiment. They found that the baseline of touching behaviors is high and can easily go unnoticed.+
Handshakes and Olfactory Behavior:Noam and Andrew discuss a study on the correlation between handshakes and olfactory behavior. The study found that people tend to bring their hand to their nose and sniff it more frequently after a handshake, and this behavior is likely driven by the ambient odor that comes in with the hand.+

15. Click Friendships

Click Friendships:Noam and Andrew discuss the phenomenon of "click friendships" and how a similarity in body odor may contribute to this. They also touch on the concept of "sticky" people in neurology who make unilateral click friendships.+
The Low Effect:Noam Sobel discusses an experiment in which body odor was used to predict friendship. Participants who smelled more similar to each other were more likely to want to be friends and rated each other as nicer and more affectionate. This suggests that body odor plays a role in building friendships.+

16. Odors & Romantic Attraction

Andrew and Noam discuss the relationship between smell and mate selection. They explain how animals and humans choose mates based on immune composition and how this affects offspring.+

17. Reproduction and Olfaction

Mammalian Reproduction:Noam explains how the sense of smell dominates the reproductive behavior of mammals and how the Bruce effect, an effect discovered by Margaret Bruce in 1959, causes a pregnant mouse to miscarry the pregnancy when exposed to the odor of a non stud male.+
Pheromone Effects:Noam and Andrew discuss the Bruce Effect, a phenomenon in which a female mouse drops her pregnancy due to the odor of a non-stud male, and the role of the Vomeronasal organ in mediating pheromone effects. While humans are believed to lack a functional Vomeronasal organ, the jury is still out on whether we experience pheromone effects through other means.+
Human Miscarriage:Noam and Andrew discuss the high rate of spontaneous miscarriage in humans, with some studies suggesting up to 90% of all pregnancies end in miscarriage due to failed implantation. They also explore the possibility of a remnant Bruce effect in humans.+
Olfaction and Pregnancy Loss:Noam Sobel discusses his study on couples experiencing unexplained repeated pregnancy loss and how olfaction and memory may play a role in the body's response. Women who experience repeated pregnancy loss have a greater ability to identify their spouse's body odor, and the brain response to stranger male body odor is altered in these women. The study aims to determine if there is a causal effect between olfaction and pregnancy loss.+

18. Social Chemo-Signals, Fear

Human Chemo Signals:Noam and Andrew discuss the concept of pheromones in humans and the semantics surrounding the term. They highlight the importance of chemo signals and how they influence human behavior, citing the example of the "smell of fear" as a widely studied chemo signal emitted by humans.+
Smelling Fear:Noam explains how fear is contagious and how humans and dogs can smell fear. Andrew raises questions about the smell of safety and how it relates to mate choice and mourning periods.+
Importance of Smell:Andrew and Noam discuss the importance of our sense of smell and how it affects our behavior and emotions. They use examples to highlight the significance of our olfactory system in our daily lives.+
The Power of Smell:Andrew and Noam discuss the power of smell and how it affects our preferences, from perfume to body odor to the smell of loved ones and pets. They also touch on the science behind why certain smells are more appealing than others.+

19. Aggression and Hexadecanal

Human aggression and social buffering:Eva Mishour's study on aggression led to the discovery of Hexadecanal, a molecule that promotes social buffering in mice. The highly conserved receptor for this molecule in mammals led to the hypothesis that it could be a universal mammalian signal. The Tyler aggression paradigm was used to study the effects of Hexadecanal on human aggression.+
Provocation and Punishment:Noam and Andrew discuss a game experiment where participants are provoked and punished. The experiment involves dividing money and reacting to loud noises. The discussion highlights the psychology behind the experiment and the effects of provocation and punishment on participants.+
Aggression and Hexadecanal:Noam and Andrew discuss the effects of Hexadecanal on aggression in men and women. While it lowered aggression in men, it increased aggression in women. The conversation touches on the potential maternal protectiveness as a reason for the difference.+
Aggression and the Brain:Noam and Eva conducted an experiment that showed hexadecanalum increased aggression in women and decreased aggression in men. The study also revealed that hexadecanalum increased activity in the left angular gyrus, an area of the brain involved in social appraisal. However, the same area of the brain showed opposite functional connectivity in men and women under the influence of hexadecanalum.+
Baby Head Odor:Noam and the team discuss the chemical signals emitted by babies and how they affect the behavior of those around them. They delve into a study on the odors emanating from baby heads and discover the most abundant semi volatile in baby heads, hexadecanal, which reduces aggression in fathers and increases aggression in mothers.+

20. Menstrual Cycle Synchronization

Menstrual Cycle Coordination:Noam and Andrew discuss the coordination of menstrual cycles among cohoused women and the role of olfaction in this phenomenon. They delve into the early literature by Barbara McClintock and subsequent papers that have called this result into question.+
Olfactory Effects:Andrew and Noam discuss the McClintock study, which found that women's menstrual cycles can synchronize through olfactory communication. Noam explains the study's findings and its statistical challenges, while Andrew highlights the unique potential of olfactory effects in humans.+

21. Tears and Testosterone

The Smell of Fear:Noam and Andrew discuss the relationship between odors and hormones, specifically in relation to fear. Noam shares his lab's paradigm for generating fear and collecting body odor from first-time jumpers to find the fear molecules, which could lead to the development of blockers for cognitive receptors.+
The Mystery of Tears:Noam discusses tears as an emotional expression that has puzzled scientists for years. Darwin's book, "The showing of the emotions in man and animals," dedicated an entire chapter to tears, but could not find a functional anticipant. Noam and his team explore tears as a bodily liquid that emits in emotional situations where nonverbal communication is critical and key.+
Emotional Tears:Noam and Andrew discuss the function of emotional tears and the challenges of finding male participants who cry easily due to cultural biases. The lab has a collection of sad movies that can easily make people cry.+
Tears and Testosterone:Noam and Andrew discuss the collection of tears and the effects of sniffing them on testosterone levels. They found that tears are completely odorless, and when men sniffed women's tears, they experienced a significant reduction in free testosterone levels.+
Testosterone Effects:Andrew and Noam discuss the powerful and fast-acting effects of unbound testosterone on the body and brain. They share findings from studies on the hormone's impact on brain activity and aggression in men.+

22. Science Politics

Tears and Chemo-signaling:Noam shares the story of how their research on tears went against the thesis story of emotional tears being uniquely human. They discuss the chemo-signaling mechanism of tears in animals and how their findings went against a lab in Holland's career. They also mention a recent paper that found dogs emit emotional tears and how it influences oxytocin in humans.+
Dog Oxytocin:Andrew shares his personal experience with his dog Costello and how he believes dogs hijack the circuitry intended for child rear through oxytocin. Noam discusses a failed attempt to replicate a study on dogs shedding emotional tears and how he offered to replicate it again with the authors.+
Science Replication:Noam and Andrew discuss the importance of replication in science, sharing a story of a failed replication and the rebuttal that followed. They also touch on the ego and sociology of science and the importance of being objective in grant reviews.+

23. Food Odors & Nutritional Value

Smell and Nutrients:Andrew and Noam discuss whether the smell of food can signal nutrient content, even for things that have no odor. They reminisce about living in the same apartment and the amazing smells of the cheeseboard below.+
Olfactory Signals:Andrew and Noam discuss the possibility of olfactory signals indicating nutrient value in food. They also touch on the obesity crisis and the challenges of processed foods lacking micronutrients. Noam shares a factoid about olfactory perceptual similarity in metabolic products, and mentions companies seeking help to bring odor to engineered meat.+

24. Olfactory Insights

Olfactory Misconceptions:Noam dispels the misconception that sense of smell is subjective and highlights the cross-cultural similarities in olfactory perception. Humans are incredibly similar to one another in their olfactory perception, and pleasantness estimates are highly correlated across humans. Outliers like cilantro and guillava attract our attention, but they are few polarizing odors that divide people's opinions.+
The Science of Smell:Noam explains how our perception of odors is influenced by cultural and linguistic factors. He also highlights the importance of language anchors in other sensory systems and how the lack of them in olfaction affects our ability to perceive odors similarly.+
Perception Similarities:Noam explains how the perception of smell can be measured and compared between individuals using a similarity matrix. He also discusses how humans are more similar in their perception of taste and sound, but vary greatly in color vision.+

25. Digitizing Smell, COVID-19 & Smell

Smell in Silico:Andrew and Noam discuss the potential for generating smells through computers, specifically through search engines like Google. They touch on the idea of using smell to drive decision making and the recent developments in this area.+
Digitizing Smell:Noam discusses the active field of research dedicated to digitizing smell, which has been driven by the importance of olfaction in the COVID pandemic. He explains the recent breakthroughs in developing rules that link odor structure to odor perception, which has been a challenge until recently.+
Digitizing Smell:Noam explains how his lab developed an algorithmic framework that can predict the perceptual similarity of any two molecular mixtures with high accuracy. This framework enabled them to generate olfactory metamars, which are mixtures that are completely non-overlapping in their molecular structure but smell exactly the same. They have also generated the infrastructure for digitizing smell, which allows them to predict the odor of any molecular mixture and find a set of components that can be used to mix any odor that can be perceived.+
Smell Transmission Progress:Noam and Andrew discuss the progress made in transmitting smells over IP, with violets being the first odor successfully transmitted. While there is still much work to be done, they predict that the technology will become more practical in the future, with Google likely leading the race. The potential applications of smell transmission are vast, from dating apps to connecting with loved ones over video calls.+

26. Digitizing Olfaction

Digitizing Olfaction:Noam discusses the potential of digitizing olfaction and its implications in medical diagnosis, stating that every disease has a specific metabolic process with metabolites that have a smell. He envisions a future where each person will have an electronic nose in their bathroom for constant diagnostics.+
Gratitude and Delight:Andrew expresses his gratitude and appreciation for Noam's work in the field of science, and Noam expresses his delight in discovering that people care about his work. They discuss the importance of drive and the rare moments of reward in scientific research.+

27. Olfaction Insights

Andrew discusses the fascinating world of olfaction and chemosensation with Dr. Noam, highlighting the importance of these senses and their impact on our daily lives.+