1904 Nobel Prize in Physiology or Medicine — Ivan Pavlov

What You Will Learn in This Article

You will discover that "Pavlov's dog" was not just a simple animal experiment, but the beginning of a revolution that made human mental activity scientifically measurable. And that this is the foundation of modern neuroscience, behavioral psychology, and machine learning.

Can "Mind" Be Measured?

In the late 19th century, scientists were facing a dilemma. Heartbeat could be measured, blood pressure could be measured, and body temperature could be measured. But what about thought? Emotions? Learning? Most scientists believed that these "mental phenomena" belonged to the realm of philosophy, not science.

Pavlov was the one who broke down this barrier. Instead of subjectively interpreting mental phenomena, he invented a way to convert them into a measurable physical quantity, such as the amount of saliva secreted. This was a revolution. And this revolution began unexpectedly, while he was studying digestive fluids.

The Landscape of the Time — Empires Colliding

In February 1904, the Japanese Navy launched a surprise attack on the Russian fleet at Port Arthur. This marked the beginning of the Russo-Japanese War (1904-1905). The fact that the European power Russia was being defeated by the rising Asian nation of Japan was a tremendous shock to the world at the time.

Pavlov received the Nobel Prize during this very war. While he was measuring the saliva secretion of dogs in his laboratory in St. Petersburg, anti-war demonstrations were taking place in the streets of the same city. The following year (1905), the "Bloody Sunday" massacre occurred, and the First Russian Revolution broke out. A major shift was beginning, which would lead to the Bolshevik Revolution (1917) 13 years later.

This also had a direct impact on Korea. As a result of the Russo-Japanese War, Japan secured its dominance over the Korean Peninsula, leading to the Eulsa Treaty in 1905 and the annexation of Korea in 1910. In the same year that a European scientist was studying dog saliva, the fate of East Asia was being decisively altered.

Interestingly, Pavlov himself was in a unique position. He was a scientist who received the best treatment under the Russian Empire, but he also continued to be supported in his research under the Soviet regime. Both Lenin and Stalin considered Pavlov's research to be a national asset. In CS terms, he was a kernel module that survived even when the OS (the regime) was replaced — a core process that was too important to be removed, even when the system changed.

From Theologian to Physiologist

Ivan Petrovich Pavlov (1849-1936) was born in a rural village in Ryazan, Russia, as the son of an Orthodox priest. He originally studied theology at the behest of his father. However, in the 1860s, Charles Darwin's theory of evolution and Ivan Sechenov's theory of brain reflexes were introduced to Russia. In particular, Sechenov's Reflexes of the Brain (1863) changed Pavlov's life. The claim that mental activity is nothing more than physical reflexes in the brain. The theology student quit theology school and entered the Faculty of Natural Sciences at the University of St. Petersburg.

After graduating, Pavlov studied digestive physiology. He developed a method of surgically creating a small opening (fistula) in the dog's digestive tract to directly observe and measure the secretion of digestive fluids. This alone was already innovative. It was the first experiment to observe the normal digestive process of a living animal in real time.

A Strange Saliva — The Moment an Event Listener is Registered

This is where the "accident" happens. While conducting experiments on the secretion of digestive fluids, he noticed that the dogs began to salivate simply by seeing the food. Even at the sound of the footsteps of the animal caretaker bringing the food. Pavlov initially called this "psychic secretion," but he soon realized that this was the real treasure.

Systematic experiments began. Each time food was given, a bell was rung at the same time. After repeating this several times, the dogs began to salivate simply at the sound of the bell, even without food. Pavlov named this a conditioned reflex.

In software terms, this is the dynamic registration of an event listener. Originally, the dog's nervous system only had a basic event, food.addEventListener('contact', salivation). Pavlov's experiment dynamically registered a new event listener, bell.addEventListener('ring', salivation), through repeated pairing. A new input-output mapping was created through learning.

However, this analogy breaks down here. In software, event listeners are permanent once registered, but conditioned reflexes disappear (extinction) without reinforcement. If the bell continues to ring without food, the dog will eventually stop responding to the bell. Biological event listeners have a built-in auto-unsubscribe function.

Why Is This Important? — The Roots of Modern Science

If Pavlov's conditioned reflex is remembered only as the "dog salivating experiment," that would be a great mistake. This discovery was the direct foundation of many fields of modern science.

The Birth of Behaviorist Psychology. John Watson, B.F. Skinner, and others extended Pavlov's conditioned reflex to humans. The idea that human behavior can be explained as a chain of stimulus and response, behaviorism, dominated 20th-century psychology. It's a must-read in the first chapter of college introductory psychology textbooks.

The Foundation of Neuroscience. Thanks to Pavlov's principle of "measuring mental phenomena physically," neuroscience was able to treat the brain as a "researchable physical organ" rather than a "mysterious seat of the soul." This is the starting point for modern fMRI research and neurotransmitter research.

Structural Similarity to Machine Learning. The core of the conditioned reflex — repeatedly pairing inputs and outputs to learn new mappings — is structurally identical to supervised learning in modern machine learning. Repeatedly presenting learning data (stimulus-response pairs) to adjust the weights of the model (neural network). Pavlov showed this with dogs, and we are now doing it with GPUs.

Drug Dependence and Addiction Research. When a specific environment (place, person, smell) is repeatedly paired with drug use, that environment alone can trigger cravings and withdrawal symptoms. Modern addiction medicine is based on the conditioned reflex model.

A Man Who Remained in the Laboratory Until the Age of 87

Pavlov continued his research in the laboratory until his death in 1936 at the age of 87. His laboratory did not stop, even as he experienced four major upheavals: the Russian Empire, World War I, the Bolshevik Revolution, and the Soviet regime.

Interestingly, Pavlov was actually a man of religious sensibility. As a theology student, he continued to attend church, and he did not abandon his religious beliefs even under the Soviet regime, which made atheism its state ideology. The scientist who reduced the mind to physical reflexes was also a man of faith. However, for Pavlov, this was not a contradiction. He studied the workings of the brain, but he never denied the existence of the mind.

The bell and the saliva. This seemingly simple connection became the foundation of psychology, neuroscience, behavioral medicine, and machine learning. The greatest discoveries in science often begin with the simplest observations.