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In 1976 researcher Harry McGurk and his assistant John MacDonald were running an infant study on how babies perceive language when a technician dubbed a video of a face saying one syllable over audio of another. When they played it back, they heard neither sound. Their brains produced a third. This episode explains the McGurk effect: hear ba ba while watching lips form ga ga and you perceive da da...

For decades the medical establishment treated the adult brain as fixed hardware. This episode traces the evidence that it is not, starting with Italian anatomist Michele Vincenzo Malacarne, who in 1793 trained one animal of a littermate pair for years and found its cerebellum substantially larger. Santiago Ramón y Cajal coined the term neuronal plasticity in the early 1900s over objections from pe...

Each eye has a hole in its vision, and the brain hides it. This episode explains the physiological blind spot, the punctum caecum, which sits where the optic nerve exits through the optic disc, an area with no photoreceptors at all. It lies about 12 to 15 degrees toward the temple and 1.5 degrees below the line of sight, measures about 7.5 by 5.5 degrees, roughly the size of a fist at arm's length...

Pressing your palms against closed eyes produces a light show without a single photon entering the eye. These lights are phosphenes, from the Greek for to show light. This episode explains pressure phosphenes, including the shifting grid one scientist compared to a crumpling, fly-spotted fly screen, and how squeezing retinal ganglion cells makes them fire signals the brain can only read as light....

Déjà vu, French for already seen, strikes roughly two thirds of people at least once. French philosopher Émile Boirac coined the term in 1876 in The Future of the Psychic Sciences. This episode explains who experiences it most, including younger people, frequent travelers, heavy film watchers and people who remember their dreams, and why a 2008 study found no diagnostic link to schizophrenia. It d...

In the early 1970s, researchers hunting for a painkiller without morphine's addiction risk asked why the brain had receptors that fit a poppy extract so precisely. In 1973 they reasoned the body must make its own matching molecule, and they isolated natural opioid peptides from pig brains, called enkephalins, then similar peptides from calf brains. The word endorphin, joining endogenous and morphi...

Freezing to death is rarely the quiet drift into sleep shown in films. This episode follows the body as its core temperature falls below the normal range of 36.5 to 37.5 degrees Celsius. Below 35 degrees, mild hypothermia brings violent shivering, a racing heart and cold-induced diuresis, as blood pulled from the limbs makes the body sense too much fluid in its core. Below 32 degrees shivering sto...

Beriberi, a name said to mean I cannot, I cannot in Sinhalese, is thiamine deficiency. With a half-life of about 17 days in the body, vitamin B1 must be constantly replaced, and without it cells cannot turn glucose into usable energy. This episode describes dry beriberi, which destroys peripheral nerves; wet beriberi, which leads to high-output heart failure; and infantile beriberi, which can para...

The cone snail Conus geographus hunts by releasing a weaponized insulin that sends a fish's blood sugar crashing and leaves it sluggish enough to engulf. This episode follows insulin from that reef to the islets of Langerhans, spotted by Paul Langerhans as a Berlin medical student in 1869. It explains how beta cells release insulin to move glucose into cells through GLUT4 transporters, how glucago...

Walter Reed was born in 1851 in Gloucester, Virginia, the son of a traveling Methodist minister. He earned a medical degree from the University of Virginia before turning 18, still the youngest ever there, and a second in New York by 1870. After passing a 30-hour exam he joined the Army Medical Corps in 1875 and spent 16 years in the West, treating soldiers, Geronimo's Apaches and pioneers, saving...

Tuberculosis infected an estimated 10.7 million people in 2024 and killed 1.23 million, making it the deadliest single infectious agent on Earth. This episode traces it from skeletons dated to 4000 BC and Egyptian mummies with spinal decay to 18th and 19th century Europe, where consumption caused a quarter of all deaths. With no germ theory to guide him, Dr. John Croghan bought Mammoth Cave in Ken...

Triage comes from the French trier, to sort, a word once used for grading coffee beans and wool. This episode follows how medicine came to sort people instead, starting with the Edwin Smith Papyrus of 17th century BCE Egypt, which divided injuries into those a healer could treat, those to fight with, and those that could not be healed. Under Emperor Maximilian I of the Holy Roman Empire, the sicke...

Thomas Midgley Jr., born in 1889 in Pennsylvania to a family of inventors, carried a periodic table everywhere and treated chemistry as a practical toolkit. After joining General Motors in 1916 under Charles Kettering in Dayton, he worked through the elements looking for a cure for engine knock. Tellurium worked but smelled like rotting garlic. In December 1921 he found that tetraethyl lead stoppe...

Synesthesia, from the Greek for joined sensation, is an involuntary condition in which stimulating one sense or cognitive pathway triggers an experience in another. This episode covers some of the more than 80 documented types, from grapheme-color synesthesia, in which the letter A is overwhelmingly seen as red, to lexical-gustatory synesthesia, in which pub owner James Wannerton tastes earwax whe...

The corpus callosum is a bundle of hundreds of millions of myelinated nerve fibers linking the brain's two hemispheres. Surgeons first cut it partially in the 1930s, when Walter Dandy sought a path to deep pineal tumors, and later as a last resort for violent grand mal seizures that spread from one hemisphere to the other. This episode explains why split-brain patients seem normal in daily life an...

In 1966 NASA engineer Jim LeBlanc was testing a prototype spacesuit in a vacuum chamber when his pressurization hose came loose. Within 10 seconds his suit pressure fell to near zero, and he stayed conscious for 14 seconds, long enough to feel the saliva on his tongue begin to boil. A colleague got oxygen to him within about 25 seconds, and he walked away with an earache. This episode works throug...

In 1816 at a Paris hospital, physician René Laennec was called to examine a young woman with the signs of heart disease. Tapping her chest told him little through the extra tissue, and pressing his ear to her bare chest, the accepted method then called immediate auscultation, broke the social propriety of the day. Remembering that a pin scratched at one end of a solid piece of wood can be heard cl...

The snake oil salesman is an icon of the Old West, but this episode traces the idea to 18th century Europe, where oil from viper fat was a common treatment for rheumatism, joint pain and skin disease. Patent medicines date to 1712, when Richard Stoughton received a patent for his elixir. In America the rattlesnake became a logo rather than an ingredient, and sellers used mineral oil mixed with her...

Long before vaccines, people protected themselves from smallpox, which killed about 30 percent of those infected, by deliberately catching a mild case. This episode traces variolation from China, where healers as early as the 16th century blew powdered old scabs mixed with musk up the nose through a silver pipe, right nostril for boys and left for girls. Dried scabs carried a lower viral load. In...

In 2020, scientists drilling about 230 feet beneath the seabed of the South Pacific gyre found microbes in sediment up to 101.5 million years old, and with a few nutrients they started growing again. This episode uses that discovery to explore suspended animation, a profound slowing of metabolism in which heartbeat and breathing become nearly undetectable. It explains why humans seem shut out: the...

Botulinum toxin is described in this episode as the deadliest natural substance in chemical literature, with an estimated lethal intravenous dose of 1.3 to 2.1 nanograms per kilogram, yet millions pay to have it injected into their faces. Its story begins in 1793 in Wildbad, Germany, when 13 people fell ill and six died after eating blood sausage stuffed into a pig's stomach. Between 1817 and 1822...

Before antibiotics, a tuberculosis diagnosis came with a prescription for months of rest, fresh air and rich food in a scenic setting. This episode traces the sanatorium from English physician George Bodington, whose 1840 essay on cold air and beef, wine and milk was dismissed by The Lancet as very crude ideas, to Hermann Brehmer's 1863 facility in Silesia, which proved the model at scale. It expl...

Hermann Rorschach, vice president of the Swiss Psychoanalytic Society, designed his 10 inkblots to help diagnose schizophrenia, then died of a ruptured appendix in 1922 at 37, believing his work had failed. This episode traces how he hand drew hundreds of designs, tested them on 300 mental patients and 100 controls, and chose near perfect bilateral symmetry because subjects rejected asymmetrical f...

In the early 1920s, cattle across the northern United States and Canada began bleeding to death after minor procedures, with 21 of 22 cows dying after dehorning on one farm. This episode follows the chemical behind it. In 1921 Canadian veterinary pathologist Frank Schofield traced the deaths to moldy sweet clover silage, and in 1929 Lee M. Roderick showed it destroyed prothrombin. Between 1933 and...

Rabies is nearly 100 percent fatal once symptoms appear and nearly 100 percent preventable if treated in time, and it has stalked humanity since at least 2000 BC in ancient Mesopotamia. This episode explains how the lyssavirus enters through a bite, quietly replicates in muscle without alerting the immune system, binds acetylcholine receptors at the neuromuscular junction, and hijacks the motor pr...