1932 Nobel Prize in Physiology or Medicine — Sherrington and Adrian

What You Will Learn in This Article

You will understand how two British physiologists demonstrated how our body can move as one unit despite thousands of reflexes occurring simultaneously, and what the basic unit is that creates signals in individual neurons.

Why Does the Body Move as a Whole?

If you tap your knee, your leg kicks up. If you touch something hot, your hand immediately pulls away. If something enters your eye, your eyelid closes. These reflexes are automatically processed in the spinal cord without going through the brain.

This leads to a natural question: Our body has hundreds or even thousands of such automatic reflexes. If they all happen at the same time, why doesn't our body fall into chaos? When the knee-jerk reflex happens at the same moment as pulling your hand away from something hot, why don't we stumble? Instead, we exhibit coordinated movement.

The answer to this question in the early 20th century came from Sherrington and Adrian. Sherrington showed how these reflexes are coordinated, and Adrian experimentally determined the basic unit of this reflex – how individual neurons create signals. The combination of these two discoveries laid the foundation for modern neuroscience.

The Zeitgeist — The Depths of the Great Depression and Political Extremism

In 1932, the world was in the deepest phase of the Great Depression. The United States saw an unemployment rate of 25%. One in four members of the labor force was unemployed. In the downtown areas of New York and Chicago, shantytowns made of cardboard and corrugated iron – "Hoovervilles" – began to appear extensively. This nickname, taken from President Hoover's name, was a mocking reference to his perceived incompetence.

In the November presidential election, Franklin D. Roosevelt was overwhelmingly elected, and the United States shifted towards the New Deal the following year. This New Deal ultimately led to a significant increase in U.S. scientific research funding, including the establishment of institutions that would later become the NIH.

The situation in Germany was even more precarious. In March and April of that year, Hindenburg defeated Hitler in two presidential elections, but Hitler's popularity was already very high. In the July general election, the Nazi Party became the largest party in the Reichstag, and in January of the following year, Hitler became Chancellor. This year marked the last few months of normal functioning of the Weimar Republic.

Oxford, where Sherrington worked, and Cambridge, where Adrian worked, were relatively stable islands in this turbulent European continent. The British academic community had been less affected by the Great Depression, and at this time, Cambridge was one of the leading centers of physiology in the world.

When viewed in conjunction with Korean history, 1932 was the height of the Korean independence movement against Japanese rule. In January, Yi Bong-chang threw a bomb at Emperor Hirohito in Tokyo, and in April, Yun Bong-gil carried out the Hongkou Park bombing in Shanghai. While in Europe, research into "how the body's reflexes are integrated" was awarded the Nobel Prize, Korean independence fighters were demonstrating their will for coordinated resistance in their respective positions. It was an era in which "how individual actions have integrated meaning" was demonstrated in different contexts.

Biographical Narratives — The Oxford Master and the Cambridge Experimenter

The two laureates were from different generations and used different methodologies.

Sherrington — The Master of Integrative Theory

Charles Sherrington was born in London in 1857. At the time of receiving the award, he was 75 years old and had already devoted half his life to the study of reflexes. He studied at Cambridge and several other universities before settling at the Department of Physiology at Oxford, where he conducted research for over 30 years.

His methodology was behavioral observation and comprehensive analysis. He observed that animals with their spinal cords severed still exhibited reflexes, and he meticulously analyzed the logical structure of reflexes. What stimulus causes what reflex? What takes priority when two reflexes overlap? What reflex inhibits what other reflex?

His seminal work was The Integrative Action of the Nervous System in 1906. This book is considered one of the founding texts of 20th-century neuroscience. It was the first systematic work to describe how individual reflexes are coordinated to become the movement of a single organism.

The terms Sherrington coined are the root of modern neuroscience vocabulary: synapse, reflex arc, proprioception, reciprocal inhibition. Without these words, a modern neuroscience lecture would be impossible.

Adrian — Pushing the Limits of Measurement

Edgar Adrian was born in London in 1889. He was 32 years younger than Sherrington, from a different generation. He trained at Cambridge and remained there. His methodology was completely opposite to Sherrington's — extremely precise quantitative measurement of minute electrical signals.

The tool that allowed Adrian to make his key observations was the Capillary electrometer and its evolved form, the cathode-ray oscilloscope. These devices made it possible to visualize in real-time the extremely small electrical activity generated by individual nerve fibers or muscle fibers.

He first clearly recorded the electrical activity of individual nerve fibers in the mid-1920s. In this experiment, an amazing fact was revealed: the action potential follows the all-or-none principle. If the stimulus is weak, there is no firing at all, and even if the stimulus is strong, the size of the firing does not increase. Instead, a strong stimulus only increases the firing frequency (number of times per second).

The significance of this discovery was great. The nervous system does not transmit information by the size of the signal, but by the frequency of the signal. The basic firing principle of neurons that we know today was established in this experiment.

Key Achievements — Reflex Integration as Seen Through the Lens of an Event Bus

Reflex Arc = The Minimal Circuit

The reflex arc established by Sherrington is a circuit like this:

1. Sensory neurons receive a stimulus (e.g., stretching of the knee tendon).
2. This signal is transmitted to the synapse in the spinal cord.
3. Motor neurons are activated.
4. The muscle contracts (the leg kicks up).

This circuit is very fast because it does not go through the brain. It is completed in 50 to 200 milliseconds. The problem is that there are thousands of such circuits in the body operating in parallel.

A CS analogy is naturally applicable here. This is similar to a combination of an event bus and a preemptive scheduler.

Consider a web browser. Click events, scroll events, keyboard events, mouse movement events — dozens or even hundreds of events occur per second. If these events were processed naively in parallel, the screen would immediately break. However, the reason the browser does not break is that the event bus manages priority and exclusion rules. Some events cancel out other events, and some events are ignored if they overlap.

What Sherrington revealed was exactly this. The synaptic layer in the spinal cord is not just a signal transmitter, but a coordinator that includes reciprocal inhibition. When the flexor reflex in the right arm is activated, the extensor reflex on the opposite side is automatically inhibited. Otherwise, the two muscles would pull against each other, and no movement would occur.

Adrian's discovery added experimental data to this. How does this coordinator actually work? Each neuron carries information in a "firing frequency" channel. A strong stimulus fires 100 times per second, and a weak stimulus fires 10 times per second. This frequency pattern acts as a priority signal on the event bus.

However, this analogy breaks down here. The event bus is a data structure that we explicitly design. However, the coordination rules of the nervous system are created by evolution, and it is often an unresolved question why a particular reflex is wired to inhibit a particular reflex. And the higher levels of the brain can also consciously override spinal reflexes. An example is that we can consciously suppress the reflex that causes us to immediately pull our hand away when we touch something hot (e.g., to prevent dropping a pan while cooking). This multi-layered override structure is much more complex than a pure event bus.

All-or-None: The Unexpected Existence of a Digital Signal

One of the most surprising aspects of Adrian's discovery is that neural signals are essentially digital. This was contrary to the intuition of people in that era. The assumption was that nature would be analog. However, the action potential of a neuron was a binary signal of yes/no, firing/no firing.

This discovery had unexpected implications 30 years later in the age of computers. People like Norbert Wiener, McCulloch, and Pitts used this binary characteristic of neurons to create the theoretical foundation of artificial neural networks. The roots of today's deep learning are partly in this observation by Adrian.

Why Is It Important?

The Nobel Prize awarded to Sherrington and Adrian is still valid today at three levels:

Neuroscientific Level: All of 20th-century neuroscience was built on the vocabulary and methodology created by the two men. Synapse, reflex arc, action potential, firing frequency — without these concepts, modern brain research would be impossible.

Medical Level: The diagnosis and treatment of neurological diseases such as Parkinson's disease, multiple sclerosis, and amyotrophic lateral sclerosis (ALS) are based on the Sherrington-Adrian framework. Each disease is understood as a defect occurring at a particular level of this reflex/electrical signal system.

Artificial Intelligence Level: The neuron model in deep learning is a geometric expansion of Adrian's firing frequency concept. Activation functions, sigmoid functions, ReLU — these are mathematical formalizations of the "fire/no fire" principle.

They left us with a lesson: "To understand the integrated behavior of a complex system, one must experimentally determine the principles of individual components and then logically integrate them into rules of interaction." Sherrington started from integration and moved towards principles, and Adrian started from principles and moved towards integration. The point where the two directions met was the gateway to neuroscience.

Even as you read these sentences, billions of neurons in your brain are firing dozens or even hundreds of times per second to process these sentences. The principles of these individual firings were revealed in the oscilloscope in Cambridge 90 years ago.

Summary of the Principles of Neural System Integration: Sherrington established the logical structure of the reflex arc and the rules of reciprocal inhibition, and Adrian experimentally determined that individual neurons transmit information by the frequency of "fire/no fire." The combination of these two discoveries made it possible to understand how the nervous system coordinates numerous individual events into integrated behavior.

→ Experience it through coding: DevBench — Event Buses and Priority Scheduling → Learn about CS concepts: DryBench — Interrupts and Coordination Preemption