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Huberman Lab
Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior
May 1, 2023
03:10:02
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Quick takeaways
- Humans have an incredible sense of smell capable of detecting odors at very low concentrations, surpassing most instruments.
- The alternating airflow through the nostrils in the nasal cycle, influenced by the sympathetic and parasympathetic nervous systems, may impact brain function.
- Olfactory testing could be a valuable non-invasive tool for early detection of neurodegenerative diseases like Alzheimer's and Parkinson's.
- Congenital anosmia, the absence of the sense of smell from birth, has social and health impacts that need further research.
- Exposure to hexadecanal has differing effects on aggression in men and women, highlighting the complex role of chemosignals and aggression.
- Further research is needed to fully understand the potential role of chemosensing in menstrual cycle synchronization among women.
Deep dives
Humans have a remarkable sense of smell
Humans have an incredible sense of smell, capable of detecting odors at very low concentrations. For example, our detection threshold for certain odors is 0.2 parts per billion, which surpasses the capabilities of most instruments. Humans also have the ability to track scent trails, similar to dogs. This was demonstrated in an experiment where participants followed a scent trail blindfolded and were able to do so successfully. Additionally, humans undergo a nasal cycle, where airflow alternates between the nostrils every two and a half hours on average. This nasal cycle is influenced by the balance between the sympathetic and parasympathetic nervous systems, and it has been found to be linked to autonomic arousal.
The potential impact of the nasal cycle on brain function
The alternating airflow through the nostrils in the nasal cycle is not directly related to olfaction, but it may have implications for brain function. Research suggests that nasal inhalation affects cognitive processing. For example, visual spatial processing has been found to be better during nasal inhalation compared to exhalation. It is believed that nasal inhalation may influence neural activity patterns and timing in the brain, potentially impacting cognition. However, more research is needed to fully understand the extent and mechanisms of this phenomenon.
The significance of olfactory testing in healthcare
The olfactory system presents promising opportunities for non-invasive testing in healthcare. Olfactory loss is often an early indicator of neurodegenerative diseases such as Alzheimer's and Parkinson's. Regular olfactory testing could provide valuable insights, but its implementation has been limited due to the lack of precise olfactometers or standardized tests. However, tests like the University of Pennsylvania Smell Identification Test (UPSIT) and Sniffing Sticks have been developed and shown potential in detecting olfactory dysfunction. With the advancement of olfactory measurement devices, it may be possible to incorporate olfactory testing as a routine diagnostic tool.
Congenital anosmia and its impact
Congenital anosmia, the absence of the sense of smell from birth, affects a small percentage of the population. Surprisingly, the average age of diagnosis for congenital anosmia is around 14 years old. Many individuals with congenital anosmia suffer socially, experiencing reduced social and romantic interactions. Studies have even shown that congenital anosmia is associated with shorter lifespans. The exact causes and mechanisms of congenital anosmia are not well understood, but the condition does not involve the absence of olfactory bulbs. However, further research is needed to fully comprehend congenital anosmia and its impact on individuals' lives.
Effects of Hexadecanal on Aggression in Men
In a study conducted by Eva Michure, it was found that exposure to hexadecanal decreased aggression in men. This molecule, known for promoting social buffering in mice, was shown to have a calming effect on male aggression in humans.
Effects of Hexadecanal on Aggression in Women
Contrary to the results in men, exposure to hexadecanal increased aggression in women. Women who were exposed to this molecule displayed higher levels of aggression compared to the control group. This unexpected finding highlights the complex role of chemosignals and aggression in differing genders.
Coordinated Menstrual Cycles
The idea of menstrual cycle synchronization among women has been widely discussed, but the scientific literature remains inconclusive. The seminal research by Martha McClintock in 1971 initially supported this phenomenon, but subsequent studies have questioned its validity. More research is needed to fully understand the potential role of chemosensing in the coordination of menstrual cycles.
The Smell of Fear and Social Signaling
Research has shown that humans emit a specific body odor when experiencing fear and this odor can influence the behavior of others. The smell of fear has been found to increase autonomic arousal and can be considered contagious. This highlights the role of chemosignals in social signaling and the impact they can have on interpersonal relationships.
Research on Olfaction and Chemosensation
Dr. Noam Sobel discusses the fascinating field of olfaction and chemosensation. He explains the complex biology behind our sense of smell, including the role of hormones and the intricate architecture of the olfactory system. Dr. Sobel highlights the connection between smell and human behavior, including social and emotional responses. He discusses his lab's groundbreaking work in understanding the chemical signals emitted by humans, such as the effects of body odor on menstrual cycles. He also delves into the potential for digitizing smell, which could have implications for various industries, from food to medical diagnostics.
Perception of Smell and Individual Variability
Contrary to popular belief, humans have a high level of similarity in their perception of smell. Dr. Noam Sobel explains that while there are outliers who may have subjective preferences for certain odors, the overall correlation in pleasantness ratings for odors among individuals is high. He highlights the misconception that smell is highly subjective and emphasizes the shared perception experienced by most people. Dr. Sobel also discusses ongoing research in understanding the relationship between odor structure and perception, as well as efforts to digitize smell for various applications.
The Future of Digitizing Smell
Dr. Noam Sobel discusses the exciting developments in digitizing smell and its potential implications. He shares the progress his lab has made in algorithmic frameworks that can predict the perceptual similarity of different molecular mixtures. This has enabled the creation of olfactory metamares, where non-overlapping mixtures can evoke the same smell. Dr. Sobel highlights ongoing efforts to further refine odor primaries that can be used to recreate any smell. He also envisions a future where digitized smell could have medical applications, such as detecting diseases through scent analysis.
Challenges and Future Directions
Dr. Noam Sobel discusses the challenges and future directions in the field of olfaction and chemosensation. He mentions the efforts of companies like Google to digitize smell and predicts that advancements in this area will have a profound impact on various industries. He also emphasizes the need for further research to understand the complex relationship between odor structure and perception. Dr. Sobel concludes by expressing his optimism for the future of smell research and the potential breakthroughs that lie ahead.
In this episode, my guest is Noam Sobel, PhD, professor of neurobiology in the department of brain sciences at the Weizmann Institute of Science. Dr. Sobel explains his lab’s research on the biological mechanisms of smell (“olfaction”) and how sensing odorants and chemicals in our environment impacts human behavior, cognition, social connections, and hormones. He explains how smell is a crucial component of “social sensing” and how we use olfaction when meeting new people to determine things about their physiology and psychology, and he explains how this impacts friendships and romantic partners. He explains how smell influences emotions, hormone levels, memories and the relationship between breathing and autonomic homeostasis. He describes how smell-based screening tests can aid disease diagnosis and explains his lab’s work on digitization of smell — which may soon allow online communication to include “sending of odors” via the internet. Dr. Sobel’s work illustrates how sensitive human olfaction is and how it drives much of our biology and behavior.
For the full show notes, visit hubermanlab.com.
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Timestamps
(00:00:00) Dr. Noam Sobel
(00:04:03) Sponsors: LMNT & Waking Up
(00:06:46) Olfaction Circuits (Smell)
(00:14:49) Loss & Regeneration of Smell, Illness
(00:21:39) Brain Processing of Smell
(00:24:40) Smell & Memories
(00:25:11) Sponsor: AG1
(00:29:07) Humans & Odor Tracking
(00:39:25) The Alternating Nasal Cycle & Autonomic Nervous System
(00:48:18) Cognitive Processing & Breathing
(00:54:47) Neurodegenerative Diseases & Olfaction
(01:00:12) Congenital Anosmia
(01:06:19) Handshaking, Sharing Chemicals & Social Sensing
(01:15:07) Smelling Ourselves & Smelling Others
(01:22:02) Odors & Romantic Attraction
(01:24:58) Vomeronasal Organ, “Bruce Effect” & Miscarriage
(01:40:20) Social Chemo-Signals, Fear
(01:50:26) Chemo-Signaling, Aggression & Offspring
(02:03:57) Menstrual Cycle Synchronization
(02:12:11) Sweat, Tears, Emotions & Testosterone
(02:27:46) Science Politics
(02:37:54) Food Odors & Nutritional Value
(02:45:34) Human Perception & Odorant Similarity
(02:52:12) Digitizing Smell, COVID-19 & Smell
(03:05:50) Medical Diagnostic Future & Olfaction Digitization
(03:10:55) Zero-Cost Support, YouTube Feedback, Spotify & Apple Reviews, Sponsors, Momentous, Social Media, Neural Network Newsletter
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