How Smell, Taste & Pheromone-Like Chemicals Control You

In this solo episode on chemical sensing, Huberman explains how the sense of smell works through three neural pathways (innate, learned, and the controversial accessory/pheromone system) and how the act of sniffing itself boosts brain alertness and learning. He covers taste, detailing the five (possibly six) taste receptors, why each evolved, and how taste receptors also appear in the gut and gonads. He provides practical tools like nasal breathing, sniff training to enhance smell and taste, and experiments with miracle berry. Finally he examines chemical signaling between humans, from women's tears lowering men's testosterone to the unconscious eye-touching people do after shaking hands.

• A Science paper found that men who smelled women's emotional tears had significantly reduced testosterone and dampened brain areas linked to sexual arousal.
  00:17:25
• Inhaling itself raises brain arousal and learning capacity while exhaling causes a dip, independent of what you smell.
  00:31:07
• Taste receptors for sweet and umami are expressed not just on the tongue but in the gut and even on the ovaries and testes.
  01:28:27
• Charles Zuker's lab swapped sweet and bitter receptors in mice, making them avoid sugar water and avidly drink bitter solutions.
  01:41:14
• A Weizmann study found people almost always touch their eyes within seconds of a handshake, subconsciously sampling the other person's chemicals.
  01:53:48
• Carnivores like tigers lack sweet receptors entirely but have umami sensitivity at least 5,000 times that of humans.
  01:22:39
• Smelling salts (ammonia) work by triggering the innate nose-to-amygdala fear pathway, jolting you awake like six espressos at once.
  00:35:47

• Olfactory neurons are unique in the brain because they are continually replenished throughout life, roughly every three to four weeks.
  00:44:08
• Concussion severity and recovery can be partly gauged by how fully a person regains their sense of smell after a head injury.
  00:50:37
• A single gene variant determines whether microwave popcorn smells pleasant or like vomit, and whether you can smell asparagus in urine.
  01:00:07
• The high-school diagram of a tongue map with separate taste zones is complete fiction; receptors are intermixed across the tongue.
  01:05:58
• Bitter receptors connect directly to the brainstem gag reflex to stop us swallowing poisons.
  01:09:35
• Diego Bohorquez's lab showed gut neurons sense fat, sugar, and amino acids and signal dopamine via the vagus nerve, driving cravings independent of taste.
  01:15:22
• Pandas have no umami receptors but heightened sweet receptors, while their carnivore counterparts are the reverse.
  01:24:14
• The Coolidge effect, recovery of mating vigor when a novel partner is introduced, runs in both males and females and is purely odor-driven.
  01:43:18
• There is no essential carbohydrate or sugar, but everyone needs essential amino acids and fatty acids to survive.
  01:09:03
• The cringe-inducing feeling of fingernails on a chalkboard is the touch and visceral component, not just the sound.
  01:33:22