Ivan Pavlov

Today is the birthday of physiologist Ivan Pavlov, born in Ryazan, in central Russia (1849). His father was the village priest, and Pavlov was all set to follow in his footsteps - even enrolling in theological seminary - when he read Darwin's work and became interested in the study of science. He left the seminary and began a course of study in physics, mathematics, and natural sciences at the University of St. Petersburg; later he received his medical degree at the Imperial Medical Academy. He left religion behind because he couldn't reconcile his passion for scientific proof with a life of faith, and was surprised when he came across other scientists who were religious. One day, walking to his laboratory, he saw a medical student cross himself outside a church. "Think about it!" Pavlov told his colleagues. "A naturalist, a physician, but he prays like an old woman in an almshouse!"

In 1890, he was named head of the Physiology Department at the Institute for Experimental Medicine, and five years later he was named Chair of Physiology at the Imperial Medical Academy. It was during this time that he did his most groundbreaking work. In 1903, he published a paper called "The Experimental Psychology and Psychopathology of Animals." In it, he explained his theory of conditional reflexes. Unlike innate reflexes, which are instinctual, conditional reflexes are learned. Pavlov came up with this theory in the course of studying the digestive systems of dogs. He noticed that the dogs would begin salivating when the lab assistant brought in their food; this was a natural reflex, and it didn't surprise him. But then after a while, the dogs began drooling whenever the lab assistant entered the room, even if there was no food present. Pavlov speculated that the dogs' behavior had changed because they had learned to associate the presence of the lab assistant with the presentation of food. He turned on a metronome at the same time that the dogs were fed. Eventually, the dogs would salivate whenever they heard the metronome - even without food - which meant that Pavlov had created a new, learned reflex in his subjects. He was even able to fine-tune the response so that it only happened when the metronome was set at a particular speed. He also learned that the reflex could be unlearned: if he used the metronome too many times without later providing food, the dogs stopped associating the sound with a meal, and they stopped salivating.
-Writer's Almanac