Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior | Huberman Lab Podcast
Andrew Huberman・2 minutes read
Humans have a remarkable sense of smell that affects interactions, health, and relationships, with research exploring topics from olfactory regeneration to chemosignaling and body odor. The complex interplay of scents, emotions, hormones, and behavior underscores the importance of olfaction in human life.
Insights
- Humans have a strong sense of smell comparable to dogs, allowing them to sense the chemical world around them.
- Tears from others can significantly affect hormone levels.
- Trauma, especially to the back of the head, can lead to a loss of the sense of smell due to damage to the olfactory nerve.
- Loss of smell, especially due to conditions like COVID, can be distressing, with a general rule suggesting that if smell isn't regained within a year to a year and a half, recovery is unlikely.
- Olfactory training, involving intentional and constant exposure to various scents, has shown success in aiding olfactory recovery, potentially more effective than alpha lipoic acid.
- The alternating airflow through nostrils may reflect autonomic nervous system balance, with potential implications for control through practices like yoga.
- The debate over the study's replication and results highlighted the complexities of scientific research, with disagreements over methodology and interpretation leading to rebuttals and further investigations.
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Recent questions
How does the sense of smell impact human interactions?
The sense of smell plays a significant role in human interactions, influencing stress levels, hormone levels, and subconscious brain functions. Humans have a strong sense of smell comparable to dogs, allowing them to sense the chemical world around them. Interacting with others involves exchanging chemicals, and tears from others can significantly affect hormone levels. Research has shown that individuals are constantly sensing their own odors, which can influence cognition and behavior. Olfaction involves receptors in the olfactory epithelium, transducing odorants into neural signals via the olfactory nerve to the olfactory bulb. Overall, the sense of smell is a powerful tool that impacts various aspects of human communication and relationships.
Can the sense of smell be lost permanently?
Loss of the sense of smell can occur due to various factors, including trauma, neurodegenerative diseases, or conditions like COVID-19. Trauma, especially to the back of the head, can lead to a loss of smell due to damage to the olfactory nerve. Complete severing of the olfactory nerve results in permanent loss, as sensory neurons typically do not regenerate in adult humans. However, partial severing or retention of some nerve tissue post-injury increases the chances of recovery due to neuron growth along existing pathways. Studies have shown that if smell isn't regained within a year to a year and a half, recovery is unlikely. Certain treatments like alpha lipoic acid have shown potential in accelerating smell recovery, but the loss of smell can be distressing and have long-term implications for an individual's quality of life.
How does the nasal cycle affect human physiology?
The nasal cycle involves alternating airflow between nostrils every two and a half hours on average, reflecting the autonomic nervous system's balance. This cycle is linked to the state of alertness or sleepiness of an individual. The alternating airflow through nostrils may have implications for autonomic nervous system balance, with potential effects on practices like yoga. Studies have shown that nasal breathing can shape cognition, modulate neural activity, and potentially influence brain functions. Additionally, a wearable device called the nasal halter has been developed to measure nasal airflow as a potential disease marker, distinguishing between ADHD and non-ADHD adults. Overall, the nasal cycle is a fascinating aspect of human physiology that can impact various bodily functions and behaviors.
How does olfactory training aid in smell recovery?
Olfactory training involves intentional and constant exposure to various scents and has shown success in aiding olfactory recovery. Studies suggest that olfactory training may be more effective than treatments like alpha lipoic acid in regaining the sense of smell. Participants in studies involving olfactory training have shown improvement in tracking odors and speed in tracking scent trails. Olfactory neurons are unique in their ability to regenerate in adult mammals, and olfactory training may stimulate this regeneration process. The training can help individuals differentiate between different scents, improve their ability to detect odors, and potentially enhance their overall olfactory function. Overall, olfactory training is a promising method for individuals looking to recover their sense of smell.
How does body odor influence human relationships?
Body odor plays a significant role in human relationships, influencing attraction, comfort, and social bonding. Research has shown that individuals imprint on specific scents, creating strong emotional connections and feelings of comfort. Studies on aggression and chemosignaling have revealed molecules like hexadecanal that can promote social bonding and reduce aggression. Human studies have demonstrated that body odor similarity can predict friendship and contribute to building relationships. The concept of "click friendships," immediate deep connections between individuals, has been linked to similarity in body odors. Overall, body odor can impact personal preferences, relationships, and social interactions, highlighting the complex interplay between scents and human behavior.
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Summary
00:00
"Human Olfaction: Science of Smell"
- The Huberman Lab podcast discusses science and science-based tools for everyday life, hosted by Andrew Huberman, a professor at Stanford School of Medicine.
- Dr. Noam Sobel, a neurobiology professor at the Wiseman Institute of Science, studies olfaction and chemosensation.
- Humans have a strong sense of smell, comparable to dogs, allowing them to sense the chemical world around them.
- Interacting with others involves exchanging chemicals, impacting stress levels, hormone levels, and subconscious brain functions.
- Tears from others can affect hormone levels significantly.
- Humans experience alternating nostril breathing patterns, reflecting their nervous system's state of alertness or sleepiness.
- Dr. Sobel's laboratory discovered that individuals are constantly sensing their own odors, influencing cognition and behavior.
- Dr. Sobel's research at UC Berkeley and the Wiseman Institute revealed human olfaction's remarkable abilities, including following scent trails.
- Olfaction involves receptors in the olfactory epithelium, transducing odorants into neural signals via the olfactory nerve to the olfactory bulb.
- Trauma, especially to the back of the head, can lead to a loss of the sense of smell due to damage to the olfactory nerve.
14:26
"Olfactory Nerve Damage and Recovery Methods"
- The brain experiences forward and backward movement in the skull's liquid, causing potential damage to the olfactory nerve.
- Complete severing of the olfactory nerve results in permanent loss, as sensory neurons typically do not regenerate in adult humans.
- Partial severing or retention of some nerve tissue post-injury increases the chances of recovery due to neuron growth along existing pathways.
- Loss of smell, especially due to conditions like COVID, can be distressing, with a general rule suggesting that if smell isn't regained within a year to a year and a half, recovery is unlikely.
- Alpha lipoic acid has shown potential in accelerating smell recovery, with studies supporting its effectiveness in aiding olfactory regeneration.
- Smelling involves multiple sensory systems, including the trigeminal nerve, which can contribute to the perception of odors alongside the olfactory nerve.
- Olfactory training, involving intentional and constant exposure to various scents, has shown success in aiding olfactory recovery, potentially more effective than alpha lipoic acid.
- Olfactory neurons are unique in their ability to regenerate in adult mammals, with studies suggesting varying levels of turnover in the human olfactory system compared to other mammals.
- Olfactory receptors converge in the olfactory bulb, forming glomeruli that reflect receptor subtypes and their responses to specific molecular shapes.
- Olfactory information is processed in the primary olfactory cortex, piriform cortex, and rhino cortex, with projections to various brain regions, highlighting the strong connection between smell and memory formation, potentially more robust than other sensory memories.
29:42
Remarkable human sense of smell and tracking
- Humans have a remarkable sense of smell, with a detection threshold of 0.2 parts per billion for mercaptans.
- Participants in a study could detect an odorant at 10 to the negative 12 molar in liquid, equivalent to a drop in two Olympic size swimming pools.
- A study involved having participants follow an odor trail while deprived of vision and somatic sensation, showing significant improvement in tracking ability.
- The study began informally at a lab picnic, where a graduate student successfully tracked a chocolate trail blindfolded.
- Participants in the formal study were completely deprived of sensory input, with a consistent odor path generated in the grass using buried twine.
- Participants were measured using nasal airflow sensors, rtk GPS for tracking, and a nasal prosthesis to test the impact of two nostrils versus one on tracking ability.
- Participants could track odors effectively from the start, with training improving their speed in tracking.
- The study also explored the nasal cycle, where airflow alternates between nostrils every two and a half hours on average, linked to autonomic nervous system balance.
- A wearable device called the nasal halter was developed to measure nasal airflow as a potential disease marker, distinguishing between ADHD and non-ADHD adults.
- The alternating airflow through nostrils may reflect autonomic nervous system balance, with potential implications for control through practices like yoga.
44:56
"Nasal Breathing's Impact on Cognition and Health"
- 14 yoga teachers were studied to see if they could control the flow of air through their nostrils by thought alone, but none were successful.
- The study aimed to understand if the alternating flow through nostrils reflects the autonomic nervous system's activity during stress.
- Experiments involving exposure to pain through cold water hand exposure showed a potential shift in nasal balance due to autonomic arousal.
- The nasal cycle involves olfactory receptors converging in the brain, with information processing linked to nasal inhalation.
- Visual spatial processing was found to be better during nasal inhalation compared to exhalation, suggesting a link between nasal breathing and cognitive processing.
- Nasal breathing is advocated for health reasons, with studies showing it shapes cognition and modulates neural activity.
- Loss of the sense of smell is an early sign of neurodegenerative diseases like Parkinson's and Alzheimer's, potentially due to pathogens entering the brain through the olfactory system.
- The lack of digitization in olfaction has hindered the development of olfactory tests for tracking neurodegeneration over time.
- Existing olfactory tests like the UPSIT and Sniffing Sticks are not as convenient as visual or auditory tests due to poor stimulus control.
- Olfactory testing in newborns is not as common as vision and auditory testing, despite the potential significance in early detection of neurological issues.
01:00:27
Congenital Anosmia: Social Challenges and Olfactory Responses
- Congenital anosmia is the absence of the sense of smell from birth, affecting around half a percent of the population.
- Shockingly, the average age for diagnosing congenital anosmia is 14 years old, leading to delayed awareness of the condition.
- Individuals with congenital anosmia face social challenges and a range of negative life events, including a shorter lifespan and reduced social and romantic interactions.
- Some individuals with congenital anosmia lack olfactory bulbs, with most having shriveled or absent olfactory bulbs in adulthood.
- Common syndrome, associated with hypogonadic development in men, is prevalent among individuals with congenital anosmia.
- Handshaking behavior has been studied to reveal that people tend to touch their nose more frequently after handshakes, indicating an olfactory response.
- Participants in an experiment showed increased nose-touching after handshakes, with a clear link to olfactory behavior.
- Nasal airflow measurements confirmed that individuals were sniffing their hands after handshakes, indicating an olfactory response.
- An experiment involving pleasant and unpleasant odors emitted from an experimenter's hand showed that individuals were more likely to bring their hand to their nose after sensing an odor.
- Self-sampling behaviors, such as smelling one's hand after a handshake, may involve a comparison of self to others and reflect subconscious olfactory processing.
01:15:30
Body odor similarity predicts friendship formation.
- Click friendships are immediate, deep connections between individuals that are poorly understood in literature but widely experienced.
- A study was conducted in Israel to investigate if similarity in body odor contributes to click friendships.
- Click friends were recruited, and their body odors were sampled using a protocol involving odorless shampoo and sleeping in a specific t-shirt.
- An electronic nose device was used to analyze body odors, revealing that click friends had more similar body odors than expected by chance.
- Participants were able to distinguish click friends from non-click friends based on body odor similarity.
- To test causality, strangers were involved in a social interaction game and rated each other, with results showing a correlation between body odor similarity and friendship perception.
- The study suggests that body odor similarity can predict friendship and plays a role in building relationships.
- The concept of constantly smelling oneself, termed the "low effect," is related to the study's findings on body odor and friendship.
- In mammals, including humans, body odor and immune composition influence romantic attraction and partner selection.
- The Bruce effect, where a pregnant mouse miscarries upon exposure to a non-stud male's odor, demonstrates the powerful impact of chemosensation on behavior.
01:31:58
Human Pregnancy Loss: Olfaction and Causal Experiments
- Postmortem studies in humans are complex due to the altered state of tissues compared to animal studies.
- The structure in question is considered vestigial in humans, with no evidence of functionality.
- Humans may experience a phenomenon similar to the Bruce effect, with a high rate of spontaneous miscarriages, especially in the first trimester.
- Studies suggest a significant number of human pregnancies end in miscarriage, with a portion remaining unexplained.
- A group of couples experiencing unexplained repeated pregnancy loss was studied, with some facing up to 12 consecutive losses.
- Olfaction and response to male body odor were tested in couples experiencing repeated pregnancy loss.
- Women experiencing repeated pregnancy loss showed a heightened ability to identify their spouse's body odor compared to controls.
- Brain response to stranger male body odor differed significantly in couples experiencing repeated pregnancy loss.
- Olfaction alterations were observed in spontaneous repeated pregnancy loss cases, prompting further causal experiments.
- Plans for a causal experiment involving blocking smell in couples trying to maintain a pregnancy were discussed.
01:47:57
Scent preferences impact relationships and aggression levels.
- Our olfactory sense often guides our preferences, leading us to favor certain scents over others, such as body odors or perfumes.
- Personal scent preferences can impact relationships, as differing preferences in smells can create challenges between partners.
- Imprinting on specific scents, like that of a beloved pet, can create strong emotional connections and feelings of comfort.
- Research on aggression and chemosignaling in mice led to the discovery of hexadecanal, a molecule promoting social bonding.
- Human studies on aggression using the Tyler Aggression Paradigm (TAP) revealed that hexadecanal reduced aggression in men but increased it in women.
- Further experiments, including fMRI scans, showed that hexadecanal affected brain activity differently in men and women, influencing aggression levels.
- Functional connectivity analysis indicated that hexadecanal altered brain regions related to aggression, with differing effects in men and women.
- The observed gender-specific responses to hexadecanal may be linked to evolutionary roles in parental behavior, with maternal aggression often being protective.
- Studies on baby head odors revealed hexadecanal as a prevalent semi-volatile compound, potentially influencing parental behavior through chemosignaling.
- The abundance of hexadecanal in baby head odors suggests a role in reducing aggression in fathers and promoting protective maternal behavior, highlighting the complex interplay of scents and behavior.
02:03:53
Menstrual cycle coordination through chemosignaling research
- Martha McClintock conducted a study as an undergraduate at Wesleyan College, observing menstrual cycle coordination among co-housed women, inspired by similar effects in rodents.
- McClintock published a paper in Nature in 1971, followed by a 1998 study with graduate student Chicago Stern, where sweat from donors affected recipients' menstrual cycles.
- Sweat collected from different phases of the donors' cycles either extended or shortened the recipients' cycles, indicating a chemosignaling effect, with opposing effects based on collection time.
- McClintock's findings have faced scrutiny due to the complexity of cyclic events and statistical challenges, with some replication efforts yielding inconclusive results.
- Despite skepticism, McClintock's study remains intriguing for its real-world implications and unique exploration of olfactory effects in humans.
- Research on the relationship between odors and hormones, particularly fear, has become a focus in human social chemosignaling studies, with sweat being a common medium for analysis.
- A study on the smell of fear involves collecting body odor from first-time paratroopers to potentially identify fear molecules for therapeutic applications.
- While sweat is a prevalent medium for social chemosignaling research, tears have also been considered as potential chemical signals due to their emotional nature and lack of a clear functional antecedent.
- Darwin's exploration of emotional expressions in animals highlighted tears as an enigmatic phenomenon, leading to the hypothesis that tears could serve as chemical signals.
- Emotional tears were harvested from participants to investigate their potential as chemical signals, with challenges in recruiting male volunteers due to cultural biases surrounding crying.
02:20:07
"Film-induced tears impact hormones and behavior"
- In a study on emotional responses to films, participants were asked about scenes that made them cry, with one example being from the movie "The Champ" where the protagonist dies in his son's arms.
- The researchers collected tears from participants watching sad films, gathering a full mL of tears in about 15 minutes, noting that tears of joy did not have the same effect.
- To avoid copyright issues, the researchers had to purchase the films they used in the study, leading to a large collection of sad movies in their lab.
- Out of 100 volunteers, only about six could consistently cry in the lab, with some individuals showing a phenomenon called narrative distancing, where they emotionally detach from what they watch.
- Sniffing tears led to a significant reduction in testosterone levels within 20-30 minutes, with a 14% drop in free testosterone, a rapid and potent effect.
- An independent group from South Korea replicated the testosterone effect, confirming the original study's findings.
- Brain activity was also affected by tears, showing lowered activity in the hypothalamus and fusiform gyrus under arousing conditions, with ongoing research to replicate and expand on these findings.
- Sniffing tears was found to lower aggression in men, with implications for understanding human behavior and chemical signaling mechanisms.
- A lab in Holland disputed the original study's findings, claiming emotional tears were uniquely human, but subsequent research in rodents and dogs supported the idea of tears as a chemical signaling mechanism.
- The debate over the study's replication and results highlighted the complexities of scientific research, with disagreements over methodology and interpretation leading to rebuttals and further investigations.
02:36:18
"Subjective Smell Perception and Collaboration in Science"
- People tend to overlook details and rely on group opinions, leading to unclear conclusions.
- Common advised to publish a response if necessary and offer collaboration, which was refused.
- In science, politeness is common face-to-face, but reviews can be harsh.
- A suggestion was made to collaborate with a lab for a round table discussion.
- Smell can indicate nutrient content in food beyond what is perceived.
- There may be subconscious signals in smell that influence attraction and food choices.
- The misconception of subjective smell perception is debunked with high correlation in pleasantness estimates.
- Outliers and language application contribute to the belief in subjective smell perception.
- Similarity matrices can quantify smell perception objectively, showing high correlation in human olfactory perception.
- The importance of similarity as a measure in sensory systems is highlighted for understanding olfactory perception.
02:51:09
Advancements in Digital Smell Technology
- Color vision and olfaction are compared in terms of similarity, with color vision showing more dissimilarity than olfaction.
- Variability exists in sensory systems, but they are malleable, allowing for changes in perception.
- The potential for manufacturing smells digitally is discussed, with the idea of creating richer sensory experiences.
- Google and other companies are working on digitizing smells, with the goal of incorporating smell into computer interfaces.
- The importance of smell in decision-making and its potential for driving choices is highlighted.
- Research on olfaction has been revitalized due to the COVID-19 pandemic, increasing awareness of the significance of smell.
- A breakthrough in predicting the perceptual similarity of molecular mixtures has been achieved, allowing for the creation of olfactory metamers.
- An algorithmic framework has been developed to predict the smell of any molecular mixture accurately.
- Efforts are being made to create a set of primary components that can be used to mix any odor.
- Initial proof of concept tests have been conducted to recreate specific odors, showing promising results but still requiring further development.
03:07:20
"Future of Olfactory Diagnosis in Toilets"
- Dr. Noam Sobel discusses the potential of having a diagnostic tool in toilets for olfactory system analysis in the future.
- The conversation covers various topics such as hormones, smells, and the architecture of the olfactory system, highlighting the incredible work done in the field of olfaction.
- The speaker expresses gratitude for Dr. Sobel's pioneering work and the impact it has had, acknowledging him as a hero in the scientific community.
- The podcast host appreciates Dr. Sobel's dedication to science, expressing gratitude for his work and inviting him to share future results on the show.
