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Huberman Lab
Dr. Noam Sobel: How Smells Influence Our Hormones, Health & Behavior
May 1, 2023
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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.
1.
Introduction
5min
2.
How to Get the Best Night's Sleep
2min
3.
The Major Components of Our Ability to Smell
6min
4.
The Effects of Trauma on the Olfactory Nerve
2min
5.
The Role of Alpha Lipoic Acid in Smell Recovery
2min
6.
The Effects of Olfaloic Acid on the Olfactory System
2min
7.
The Benefits of Olfaction Training
4min
8.
The Problem With the Textbook View of How Things Work
2min
9.
The Relationship Between Smell and Memory
3min
10.
The Olfactory System and Vision
3min
11.
How to Improve Your Smell Ability
5min
12.
The Neuroscience of Nasal Airflow
2min
13.
How to Measure Sniffing Frequency in the Brain
2min
14.
The Relationship Between Sleep and Autonomic Arousal
3min
15.
How to Gain Control of Your Nasal Cycle
2min
16.
The Power of Thought
3min
17.
The Role of Nasal Inhalation in Olfaction
4min
18.
The Effect of Nasal Inhalation on Cognitive Processing
2min
19.
The Role of the Olfactory System in Neurodegeneration
2min
20.
The Invasiveness of Olfactometers
3min
21.
The Average Age of Diagnosis for Congenital Anosmia
2min
22.
The Importance of Olfactory Bulbs in Adulthood
2min
23.
The Role of Olfactory Bulbs in Olfaction
2min
24.
The Importance of Olfactory Bulbs
3min
25.
The Evolution of Hand-Shaking
3min
26.
The Effects of Handshakes on Behavior
4min
27.
The Effect of Smell on Click Friendships
3min
28.
The Effects of Random Diets on Click Friendship
5min
29.
The Relationship Between Smell and Choice of Friends
4min
30.
The Bruce Effect: A Remarkable Effect
3min
31.
The Effects of Chemosensation on the Nasal Organ
2min
32.
The Bruce Effect in Humans
2min
33.
The Bruce Effect in the First Trimester of Pregnancy
6min
34.
The Effects of Male Body Order on the Hypothalamus
2min
35.
The Problem With Pheromone Effects in Humans
4min
36.
The Smell of Safety
3min
37.
The Two Most Basic Behaviors We Have
2min
38.
The Effect of Smell on Romantic Partners
5min
39.
The Prisoner Experiment
4min
40.
The Effects of Hexadecanol on Aggression
4min
41.
Hexadeconyl: The Most Abundant Semi Volatile and Baby Hits
3min
42.
The Role of Chemosensing in Menstrual Cycles
3min
43.
The Effects of Body Odors on Coordination
4min
44.
The Relationship Between Odors and Hormones and Crying
2min
45.
The Paradox of Fear
2min
46.
The Importance of Emotion Research
4min
47.
The Effect of Tears on Ocular Function
4min
48.
The Effects of Tears on Testosterone
2min
49.
The Effects of Testosterone on Brain Activity
2min
50.
The Power of Chemo Sensory Systems and Pathways
2min
51.
The Evolution of Tears
3min
52.
How Science Works and Doesn't Work
4min
53.
How to Deal With a Rebuttal
2min
54.
The Importance of Scent in Science
2min
55.
The Effect of Smell on Nutrition
2min
56.
Order Cues on Nutrient Value
2min
57.
The Role of Scent in Metabolic Products
2min
58.
The Polarization of Nutrition on Social Media
2min
59.
The Importance of Factory Pleasantness Estimates
4min
60.
The Similarity Matrix for Andrews Perception of Smell
2min
61.
How to Generate Smells in Silico in Computers
5min
62.
The Role of Perception in Color Vision
3min
63.
How to Digitize Smell
4min
64.
Google and the Future of Science
1min
65.
How to Smell Food
3min
66.
The Spirit of Science
3min
67.
The Huberman Lab Podcast: Old Faction and Chemo Sensation
3min
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.
Thank you to our sponsors
AG1 (Athletic Greens): https://athleticgreens.com/huberman
LMNT: https://drinklmnt.com/huberman
Waking Up: https://www.wakingup.com/huberman
Momentous: https://www.livemomentous.com/huberman
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
Title Card Photo Credit: Mike Blabac
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