Exploring the World of Smell: How Olfaction Affects Our Lives
Notes on Huberman Lab Podcast Episode on How Smells Influence Our Hormones, Health & Behavior
Introduction
In a fascinating episode of The Huberman Lab Podcast, Dr. Andrew Huberman talks to Dr. Noam Sobel, a professor of neurobiology who studies olfaction and chemosensation (biological process of detecting and perceiving chemical stimuli in the environment.). They discuss how the human sense of smell can influence hormones, health, and behavior. This post provides an in-depth look at the insights and findings shared during the episode.
Understanding Olfaction and Chemosensation
Our sense of smell is an incredibly intricate and powerful tool that helps us process information from our environment and other people. Dr. Sobel's research focuses on the olfactory system, which includes orthonasal (direct) and retronasal (indirect) olfaction. The olfactory epithelium, with its millions of receptors, is responsible for detecting airborne molecules and transducing them into neural signals. These signals are then transmitted to the olfactory bulb and various parts of the brain, creating connections between scents and memories.
The Power of the Human Nose
Humans have an impressive ability to detect and track odors. A study at UC Berkeley demonstrated that people could effectively follow scent trails even without training, and their tracking abilities improved with practice.
The Nasal Cycle and Its Impact on Cognition
The nasal cycle is a fascinating phenomenon that occurs in humans, where our nostrils alternate between being the "primary" or "secondary" nostril for breathing approximately every two and a half hours on average. This cycle is directly linked to the balance in the autonomic nervous system, which comprises the sympathetic and parasympathetic systems. The sympathetic system is responsible for the "fight or flight" response, while the parasympathetic system governs the "rest and digest" functions.
According to Dr. Sobel, the nasal cycle may have a significant effect on cognitive processing. Some research suggests that people perform better on certain tasks during inhalation compared to exhalation. This is due to the fact that nasal inhalation influences the flow of information between different parts of the brain, thus affecting cognitive functions such as memory, attention, and decision-making.
Nasal Health and Disease
Loss of the sense of smell can be an early indicator of neurodegenerative diseases such as Parkinson's and Alzheimer's. However, a decline in olfactory function does not always signify the presence of these conditions. Dr. Sobel is currently developing a wearable device called "nasal halter" to measure nasal airflow in each nostril separately for 24 hours, which could serve as a potential disease marker.
Olfaction in Social Interactions
Our sense of smell plays a significant role in social interactions, as we can identify others by their body odor and even form friendships or romantic connections based on scent. Studies have shown that people with similar body odors tend to click more easily and quickly. Additionally, humans emit chemosignals that can influence the behavior or hormonal state of others, such as the "smell of fear" that increases autonomic arousal in others.
Chemical Signaling and Social Buffering
Dr. Sobel's research has shed light on the molecule hexadecanal, which promotes social buffering in mice. Theories suggest that this molecule's effects could be related to maternal protectiveness. In the Tyler aggression Paradigm, exposure to hexadecanal was found to reduce aggression in men, while increasing aggression in women.
Tears and Testosterone
Dr. Sobel's experiments with "effective criers" revealed that while tears are odorless, they have a pronounced effect on reducing free testosterone levels. A study conducted in South Korea successfully replicated the testosterone effect observed in the original study, further confirming the relationship between tears and hormonal changes.
The Future of Olfaction: Digitizing Smell
Despite the incredible potential of olfaction as a tool for tracking and communication, it has not been effectively digitized. Current devices for generating odors, such as olfactometers, are slow and contaminated, far from replicating the human olfactory system. However, there is now a renaissance in olfaction research, with companies like Google and Dr. Sobel's lab working on developing a digitized olfactory system.
Dr. Sobel's lab has made progress in developing an algorithmic framework to predict the perceptual similarity of two molecular mixtures with high accuracy. They have successfully generated olfactory metameres, which are mixtures with different molecular structures but the same perceived odor. Although there is still much work to be done, the future of digitized smell is promising.
Engineered Meat and the Role of Smell
The conversation also touched upon the emerging industry of engineered meat, with two companies asking Dr. Sobel to help make their products smell like meat. This highlights the importance of smell in creating realistic and appealing alternatives to traditional meat products.
Debunking the Misconception of Subjective Smell
Dr. Sobel debunked the misconception that the human sense of smell is incredibly subjective. He explained that while language plays a limiting role in our ability to describe smells, humans are more dissimilar in color vision than in their olfaction. This revelation emphasizes the importance of understanding and researching olfaction to better comprehend the human experience.
Conclusion
The world of smells is a fascinating and complex domain that influences our daily lives, emotions, and social interactions. As researchers like Dr. Noam Sobel continue to explore the secrets of olfaction and chemosensation, we can look forward to exciting advancements in our understanding of this remarkable human ability.