Charles Zucker triggers sweet taste in mice using lasers
- Brain lasers can evoke intense sweetness without a single gram of physical sugar.
- Synthetic sweeteners fail because human taste receptors hit strict biological intensity ceilings.
- Scent, red food dye, and high-pitched audio trick the brain into tasting extra sweetness.
Sugar is no longer required to taste sweetness.
Chemical engineers spent decades synthesizing compounds like adventame, which rank hundreds of thousands of times sweeter than table sugar on paper. Yet human palates reject them. On Radiolab, psychologist Linda Bartoshik noted that hyper-potent synthetic molecules frequently hit bitter receptors, flooding the tongue with harsh off-flavors.
The biological ceiling is the real roadblock. Rutgers professor Paul Breslin explained on the show that human sweetness receptors function like dimmer switches with fixed intensity limits. High-potency molecules hit this threshold immediately without increasing perceived sweetness. Natural sugar evades this limitation because human neural reward pathways evolved around glucose rather than chemical shortcuts.
Because receptor chemistry has hard limits, neuroscience is targeting the brain directly. Taste perception is constructed inside the cortex rather than on the tongue, leaving it open to sensory hacks. Bartoshik pointed out that strawberries taste sweeter than blueberries despite containing half the sugar, driven by volatile smell molecules traveling through the nasal cavity during chewing.
Other senses skew the calculation just as easily. Breslin noted that red food dye tricks the brain into anticipating ripe fruit, while high-pitched audio tones boost sweetness perception by up to 10 percent. On Radiolab, host Lulu Miller demonstrated that combining red dye, fruit extract, and high-pitched audio dramatically amplified perceived sweetness without adding sugar.
Columbia University neurobiologist Dr. Charles Zucker took this sensory manipulation to its logical conclusion by bypassing physical receptors altogether. Zucker mapped the exact neural pathway sweet signals travel from tongue receptors through the brain stem and thalamus to the cortex.
Using optogenetics, Zucker engineered mice to express light-sensitive proteins within their sweet-sensing cortical neurons. Firing a fiber-optic laser directly into their brains triggered a strong perception of pure sweetness without any food present in their mouths.
Sensory pleasure no longer depends on physical reality.
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The Sweetest Thing • Sep 18
- Linda Bartoshik states that strawberries taste sweeter than blueberries despite having half the sugar. This occurs because volatile odor molecules travel from the mouth to the nose, boosting the brain's sweetness signals.
- Paul Breslin notes that visual cues, such as coloring food red, artificially enhance perceived sweetness due to our evolutionary history with ripe fruit. Additionally, scientific studies show high-pitched auditory tones can increase perceived sweetness by 5% to 10%.
- Charles Zooker mapped the neural taste pathway from tongue receptors to the cortex. By genetically engineering sweet-sensing neurons in mice to respond to light, Charles Zooker used fiber-optic lasers to trigger sweetness perception without any actual sugar.
Also discussed on this episode: (6)
Nutrition (5)
- Food scientists rank sweeteners by potency using a dilution scale compared to table sugar. Under this metric, honey is 1.5 times sweeter than sugar, aspartame is 200 times sweeter, and catemfe fruit is 2,000 times sweeter.
- Adventame ranks as 20,000 times sweeter than sugar, while lugduname tops the potency scale at 300,000 times sweeter. Lugduname is not FDA-approved because tests indicate it can turn animal blood the color of chocolate.
- Linda Bartoshik argues that potency rankings do not match actual human taste intensity. Eric Walters explains this discrepancy occurs because humans possess 20 to 30 distinct bitter taste receptors but only a single sweet receptor, causing high-potency sweeteners to trigger off-flavors.
- Paul Breslin explains that human sweetness receptors operate like a dimmer switch rather than a linear scale. Increasing the concentration of a sweetener eventually reaches a sensory plateau where perceived sweetness intensity levels off.
- Linda Bartoshik asserts that the evolutionary sensation of sweetness serves as a survival reward mechanism. Glucose is the brain's primary fuel, and the sweetness of mother's milk is what stimulates newborn infants to nurse.
Space (1)
- Spanish researchers at the Center for Astrobiology discovered a vast cloud of erythrulose in the center of the Milky Way. This complex four-carbon sugar is the same molecule that gives earthbound raspberries their sweet taste.