What happened to my sense of smell?

Episode Summary

Executive Summary: This episode of Crowd Science explores the science of smell, from the corpse flower's stench to COVID-19-related smell loss. Host Anand Jagatir investigates why smells are subjective, how the olfactory system works, and why some people find certain odors pleasant while others find them repulsive. Experts discuss genetic variations in odor receptors, smell training for recovery, and the complexity of predicting how a molecule will smell.

Main Topics: The Corpse Flower and Olfactory Subjectivity (Priority: 4/5): The episode opens with a visit to Kew Gardens to smell the Titan Arum (corpse flower), highlighting how smell perception varies between individuals. Ellie Bjondin finds it slightly attractive, while Anand finds it repulsive. How Smell Works: From Molecules to Brain (Priority: 5/5): Thomas Hummel explains that odor molecules must be volatile to be smelled. They travel to the olfactory cleft, bind to receptors, and create patterns that the brain interprets as specific smells. COVID-19 and Smell Loss (Priority: 5/5): The virus infects supporting cells around smell receptors, causing temporary or long-term loss. Smell training (sniffing essential oils daily) can help regenerate neural pathways. Genetic Variation in Smell Perception (Priority: 4/5): Andreas Keller discusses how genetic differences in odor receptors cause some people to be blind to certain smells (e.g., asparagus urine) or to perceive cilantro as soapy. Predicting Smell from Molecular Structure (Priority: 3/5): Noam Sobol's lab uses electrodes in the nose to measure receptor responses and predict pleasantness of novel molecules, finding that humans agree on 90% of odors. Annabel's Hypersensitivity and the Nasal Node (Priority: 3/5): Listener Annabel finds mango and vanilla sickly. Sissel Tolaas, a 'nasal node,' collects and recreates smells from around the world, demonstrating how context and intensity affect perception.

Key Arguments: Smell is subjective due to genetic differences in odor receptors and learned associations. COVID-19 causes smell loss by infecting supporting cells, not the receptors themselves. Smell training can restore olfactory function by stimulating receptor cell turnover. Most people agree on the pleasantness of odors; disagreements are rare exceptions. Predicting smell from molecular structure is a holy grail, now partially solved by measuring neural responses. Context and language shape how we identify and perceive smells.

Data Points: Number of odor receptor types in humans: 400 - Humans have around 400 different types of odor receptors. Number of detectable odorants: 1 trillion - Humans can detect possibly as many as a trillion different kinds of odorant. Percentage of COVID-19 patients with smell loss: 60% - Up to 60% of COVID-19 patients report loss or distortion of smell and taste. Number of compounds in a rose: 275 - A rose can contain up to 275 distinct compounds. Number of odorants in lab cabinet: 1000 - Noam Sobol's lab has an odor cabinet with close to a thousand different odorants. Agreement rate on odor pleasantness: 90% - Humans agree on 900 out of 1000 molecules regarding pleasantness.

Pivotal Quotes: "You can imagine it, maybe one example is to think about reading. So you don't read characters, but you read words. And when you read a word, let's say orange, then you don't read O-R-A-N-G-E, you read orange. And that's how you can imagine that odors work." — Thomas Hummel: Explaining how odor receptors combine to form a perception of a specific smell. "The current working theory around the damage it causes is that the virus is infecting the supporting cells around the smell receptors in the lining at the top of your nose, in effects of squeezing the receptor neurons and making them ineffective." — Carl Philpott: Describing how COVID-19 leads to smell loss. "If one assumes that most responses to smells are learned, then it doesn't matter at all how things smell. What matters is that you learn the right behavior in response to it." — Andreas Keller: Discussing how learned associations can override genetic differences in smell perception.

Implications: This episode underscores the importance of smell for safety and quality of life. Smell training offers hope for COVID-19 recovery. Understanding genetic and neural bases of smell could lead to personalized therapies and better synthetic odor design.