Dr. Noam Sobel

Sponsors: ROKA, Thesis, Helix Sleep

Olfaction Circuits (Smell)

Loss & Regeneration of Smell, Illness

Brain Processing of Smell

Smell & Memories

Sponsor: AG1 (Athletic Greens)

Humans & Odor Tracking

The Alternating Nasal Cycle & Autonomic Nervous System

Cognitive Processing & Breathing

Neurodegenerative Diseases & Olfaction

Congenital Anosmia

Sponsor: InsideTracker

Handshaking, Sharing Chemicals & Social Sensing

Smelling Ourselves & Smelling Others

Odors & Romantic Attraction

Vomeronasal Organ, “Bruce Effect” & Miscarriage

Social Chemo-Signals, Fear

Chemo-Signaling, Aggression & Offspring

Menstrual Cycle Synchronization

Sweat, Tears, Emotions & Testosterone

Science Politics

Food Odors & Nutritional Value

Human Perception & Odorant Similarity

Digitizing Smell, COVID-19 & Smell

Medical Diagnostic Future & Olfaction Digitization

Zero-Cost Support, YouTube Feedback, Spotify & Apple Reviews, Sponsors, Momentous, Social Media, Neural Network Newsletter

The Huberman Lab Podcast discusses science and science-based tools for everyday life. In this episode, Dr. Noam Sobel talks about the landscape of chemosensation, specifically olfaction (sense of smell) and related abilities like pheromones. Loss of sense of smell is an early sign of neurodegenerative disease, such as Alzheimer's and Parkinson's. Congenital anosmia is the condition of being born without the sense of smell. The lab is studying the relationship between odors and hormones, specifically tears and their potential as a chemical signal. The COVID pandemic has driven a renaissance of olfaction research. An algorithmic framework has been developed to predict the odor of any molecular mixture. Olfaction digitization could lead to an electronic nose in the bathroom for diagnostics.

- The Huberman Lab Podcast discusses science and science-based tools for everyday life.
- Dr. Noam Sobel is a professor of neurobiology who studies olfaction and chemosensation.
- Humans are good at sensing the chemical world around them and can detect things as well as dogs can.
- Humans take chemicals from others when they meet and process information about them subconsciously.
- Dr. Sobel's laboratory has made many discoveries about olfaction and chemosensation, including the fact that humans are always sensing their own odors.

- The podcast is separate from the speaker's teaching and research roles at Stanford.
- The podcast aims to provide free information about science and science-related tools to the general public.
- The episode is sponsored by Roka, Thesis, and Helix Sleep, each offering products related to eyewear, nootropics, and customized mattresses and pillows, respectively.
- The speaker interviews Dr. Noam Sobel in the episode.

- Loss of sense of smell is an early sign of neurodegenerative disease, such as Alzheimer's and Parkinson's.
- Olfactory loss may be a result of a pathogen that enters the brain through the olfactory system.
- Non-invasive readouts of potential neurodegeneration, such as olfactory tests, could be useful in tracking over time.
- The reason olfactory tests are not widely used is due to the poor control of the stimulus and the lack of effective digitization.

- Congenital anosmia is the condition of being born without the sense of smell.
- It affects half a percent of the population and is usually diagnosed at age 14.
- People with congenital anosmia suffer socially and have a shorter lifespan.
- Some people with congenital anosmia have a condition called Kalman syndrome, which affects hormone production.
- Olfaction and reproduction are linked in humans and other mammals.

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1. The speaker has a strong ability to identify people by their smell.
2. Humans subconsciously code identification of people they interact with based on their smell or other aspects of their chemistry.
3. The speaker's lab has conducted studies on human behavior through the sense of smell, including handshaking and self-sampling. 
4. Handshaking leads to an increase in the behavior of bringing one's hand to their nose, which is an olfactory behavior. 
5. The behavior of self-sampling may reflect a comparison of self to other.

1. A study was conducted on click friendships, where people become close friends immediately upon meeting.
2. The study found that click friends are more similar in body odor than random dyads.
3. The electronic nose was used to extract body odor and predict friendship.
4. The study suggests that similarity in body odor may contribute to click friendships.
5. People constantly smell themselves and others, which may play a role in building friendships.

- The author admits to smelling themselves multiple times a day and finding their own smell to be neutral or pleasant.
- The relationship between smell and romantic attraction is discussed, with mice preferring to mate with those who have a different immune composition.
- Incest is strongly selected against due to the potential for higher rates of mutations.
- There is evidence of similar mechanisms in humans, with romantic odor preferences being influenced by body odor and MHC makeup.
- The topic has been extensively studied in mice and humans, but not by the author's lab.

- The Bruce effect is a remarkable effect in mammalian social chemo signaling where a pregnant mouse will miscarry if exposed to the odor of a non-stud male.
- The effect is mediated by the vomeronasal organ, which is a separate portion of the olfactory bulb that processes pheromones and is linked to the limbic system.
- Humans are thought to not have a functional vomeronasal organ, but there is a suspicion that humans may experience something similar to the Bruce effect.
- A study was conducted on couples experiencing unexplained repeated pregnancy loss, and it was found that women who experience repeated pregnancy loss can identify their spouses by their body odor with much greater acuity than the typical person.
- The study also found that olfaction is altered in spontaneous, repeated spontaneous pregnancy loss, and a causal experiment is being conducted to further investigate this.

- Humans emit chemical signals that influence each other's physiology and behavior, regardless of whether it's a classic pheromone effect or not.
- The term pheromone is problematic and not accurate for humans, so chemosignals is a more appropriate term.
- Humans emit a specific body odor when in a state of fear, which influences other humans and increases their autonomic arousal.
- Olfactory cues play a significant role in mate selection and other basic behaviors, such as food choice.

- The study was conducted by Eva Michaud, a graduate student interested in aggression.
- The study used a molecule called hexadecanal, which promotes social buffering in mice and is highly conserved throughout mammalian evolution.
- The Tyler Aggression Paradigm (TAP) was used to measure aggression in participants.
- Hexadecanal reduced aggression in men and increased aggression in women.
- The molecule is abundant in baby head odor and may be a way for offspring to protect themselves from paternal aggression and promote maternal protection.

- The text discusses the coordination of menstrual cycles among co-housed women or friends.
- Barbara McClintock discovered this phenomenon in 1971 and published a paper in Nature.
- McClintock and her graduate students conducted a follow-up study in 1998, which involved collecting sweat from donor women and depositing it on the upper lip of recipient women.
- The findings of the study have been called into question and statistics of cyclic events are complicated.
- The study is interesting because of its real-world implications and the potential for a real biological phenomenon related to olfactory effects in humans.

- The conversation is about the landscape of chemosensation, specifically olfaction (sense of smell) and related abilities like pheromones.
- Our ability to smell involves both the nose and mouth, with retronasal olfaction playing a big role in contributing to taste.
- Molecules travel up our nose and interact with about 6-7 million receptors lining the olfactory epithelium, with humans having around 350 different kinds of olfactory receptor subtypes.
- Odorants dock at a receptor and turn into a neural signal, which propagates via the olfactory nerve to the olfactory bulb in the brain.
- Losing the sense of smell due to trauma is often caused by a contricu injury to the back of the head, which severs the olfactory nerve.

- The lab is studying the relationship between odors and hormones, specifically tears and their potential as a chemical signal.
- Emotional tears were harvested from participants who could cry with ease and exposed to other participants who sniffed them.
- Sniffing tears led to a pronounced reduction in testosterone within 20-30 minutes in men, but the tears were completely odorless.
- The lab also found a dampening effect on brain activity in the hypothalamus and fusiform gyrus when exposed to tears.
- Unpublished data suggests that sniffing tears lowers aggression in men.

- The original study had three components: effect on testosterone, brain activity, and behavior.
- A lab in Holland disagreed with the tear story and tried to replicate the behavioral part but failed.
- Dogs shed emotional tears and influence oxytocin in humans.
- The author offered to collaborate with the lab in Holland but they refused.
- Science is a game of seeking facts but ego is strongly woven into it.

- The speaker asks if smell can signal nutrient contents of food in a way that is divorced from the perceived smell.
- They suggest that highly processed foods lack a direct relationship between scent, taste, and nutrient content.
- The speaker mentions a potential olfactory perceptual similarity in metabolic products.
- Two companies have asked the speaker's lab to help bring odor to engineered meat.
- The topic of nutrition is polarizing on social media.

- There is a common misconception that our sense of smell is subjective, but studies have shown that humans are actually very similar in their olfactory perception.
- The misconception is due to our attraction to outliers and our poor application of language to olfaction.
- Humans have a high correlation in their pleasantness estimates of odorants, with a correlation of about 0.8 across individuals.
- We are most dissimilar in color vision, with a variance of about 100%, while in olfaction and audition, we are about the same.
- The system is malleable, and we can learn to like or dislike an odor, just like we can learn to like or dislike a sound.

- Scientists are working on digitizing smell through computers.
- Google has an offshoot startup called Osmo that is working on digitizing smell.
- The COVID pandemic has driven a renaissance of olfaction research.
- A mini breakthrough has been made in predicting the perceptual similarity of any two molecular mixtures with high accuracy.
- An algorithmic framework has been developed to predict the odor of any molecular mixture.
- A set of components called odor primaries can be used to mix any odor that can be perceived.
- A proof of concept test was done to recreate four different odorants, with violets being the first odor ever transmitted over IP.
- Google is likely to beat other labs in the race to digitize smell, but small groups of the best and most creative people can outrun and outgun large groups.

- The olfactory equivalent of 1956 black and white TV is the current level of olfactory technology.
- In the future, with 4K odor transmission, medical diagnostics could be possible as every disease has a specific metabolic process with metabolites that have a smell.
- Olfaction digitization is not close to 4K vision and audition yet, but it could lead to an electronic nose in the bathroom for diagnostics.
- The speaker expresses gratitude for the work of the expert in the field of olfaction and chemosensation.

- The text is thanking the reader for joining a discussion about olfaction and chemosensation with Dr. Noam Sobel.
- The Sobel Laboratory's work, papers, and current/future projects can be found at a link provided in the show notes.
- The podcast can be supported by subscribing to their YouTube channel, leaving a review on Spotify and Apple, and checking out their sponsors.
- The Huberman Lab Podcast can be found on social media and has a monthly newsletter called the Neural Network Newsletter that includes podcast summaries and toolkits for various topics.
- The text ends by thanking the reader for their interest in science.

- Olfactory sensory neurons are among the few central nervous system neurons in adult humans that can regenerate or replenish themselves.
- If the olfactory nerve is completely severed, there is no chance of recovery.
- The rule of thumb for olfactory loss recovery is if you don't get it back within a year to a year and a half, you'll never get it back.
- Alpha lipoic acid can accelerate the recovery of smell, but there is not overwhelming evidence for its effectiveness.
- Olfactory training is encouraged for those with partial or complete loss of primary olfaction to keep neurons electrically active and maintain their connections.
- The human olfactory system's level of regeneration is debated, but a study using C14 levels suggested there is not as much turnover in the human olfactory bulb as there is in other mammals.

- Information from olfactory receptors synapses at the olfactory bulb
- Receptors of one subtype converge to two mirror glomeruli on the olfactory bulb
- Each receptor subtype is responsive to a small subset of different molecular shapes
- Information from the bulb projects widely to different targets in the brain
- The map that may exist on the bulb doesn't exist in the rest of the brain

- Smell and memory are closely linked.
- Olfactory memories are formed more easily and maintained longer than other sorts of memories, especially the first exposure to a smell generates a particularly robust representation.
- There is something special about olfaction, but each sensory system has its own unique tone.
- The first exposure to a smell etches it into our being, and this effect is known as the Proust effect.

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- Humans have a remarkable sense of smell, with a detection threshold of 0.2 parts per billion for mercaptans.
- A study was conducted at UC Berkeley where participants were blindfolded and deprived of other sensory input to follow an odor trail with their nose, and they were able to do so effectively.
- The study found that people can improve their ability to track scents, and within an average of four days, the rate limiting factor became the speed at which they could crawl.
- The study also found that having two nostrils contributes to better performance in scent tracking, and people performed better with two nostrils over one centralized nostril.
- Sniffing behavior was measured in the study, but it was not a major finding.

- The nasal cycle is the alternating flow of air through each nostril every two and a half hours on average.
- This cycle is linked to balance in the autonomic nervous system, which has a sympathetic and parasympathetic component.
- A wearable device called the nasal halter has been developed to measure nasal airflow and is being used as a disease marker, including for ADHD.
- The direction of causality between the nasal cycle and autonomic nervous system is currently being studied through experiments, including one involving exposure to pain. 
- Yoga practitioners were unable to willfully switch between left and right nostril flow.

- The olfactory system has mirror representations on both sides of the brain, with most information kept on one side or the other.
- The alternating nostril airflow phenomenon is not related to olfaction, but may be related to brain function and cognitive processing.
- Nasal inhalation is linked to information processing and may shape cognition, not just for olfactory information but for any type of information.
- Nasal breathing is beneficial for health and cognition, and may modulate cognitive processing.

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