The Evolution of Human Brain Science Research

Abstract：Through centuries of evolving metaphors and scientific discoveries, humanity has reached a foundational understanding of the brain: it is composed of cells (neurons), functions are distributed across different regions, and bioelectric signals drive communication between neurons. While the brain remains one of science's greatest frontiers, each era’s metaphor—whether mystical spirits, electricity, or networks—has gradually shaped our understanding, bringing us closer to unveiling the brain's true nature.

When discussing scientific research, there is a common belief: "Scientific progress and human cognitive advancement follow a spiral upward trajectory, always constrained by the era and social context." While this statement is accurate, it can be somewhat abstract. More concretely, most scientific inquiries follow a clear pattern called a "technological metaphor."

A technological metaphor simplifies understanding by comparing an unfamiliar concept to a known technology. For instance, the human brain has been metaphorically described in various ways across different eras, such as a hydraulic device, a clockwork mechanism, or a telegraph network. These metaphors shape scientific exploration, though they inevitably limit how researchers perceive and investigate the brain.

However, the human brain is not a machine—it is an organ that has evolved over 500 million years. Despite the limitations of technological metaphors, they are essential for scientific progress, as each metaphor deepens our understanding while simultaneously constraining our thinking. Let’s explore how brain science has evolved through the lens of different metaphors.

The Earliest Phase: Mysticism and Limited Observation

The initial phase of brain research, which can be called the "mystical phase," extended from ancient Greece to the 16th century. For a long time, direct observation of human organs was impossible, leading to significant misconceptions. Aristotle, for example, believed the heart was the source of emotions and sensations, a belief shared by many ancient cultures, including China, explaining expressions like "heartbroken" and "hurt heart."

The first significant advancement in brain research came from the Roman physician Galen. Serving as a gladiator doctor, he combined dissection with public demonstrations. His most famous experiment involved a pig: Galen exposed the pig’s brain and heart while keeping it conscious. When the heart was pressed, the pig continued making noises, but when the brain was compressed, the pig fell silent and lost consciousness. This dramatic demonstration led to the first brain-centric theory, suggesting the brain controlled cognition and sensation.

However, to explain how the brain functioned, Galen introduced the metaphor of "pneuma" or vital spirits—an invisible substance flowing through the brain and body. While primitive, this theory represented early attempts to understand the brain scientifically.

The Renaissance: Scientific Revolution and Anatomy

Brain research remained stagnant for nearly a millennium until the Renaissance sparked renewed scientific inquiry. In 1543, Andreas Vesalius published De Humani Corporis Fabrica (On the Fabric of the Human Body), a landmark anatomical work featuring over 700 pages and 200 illustrations, including detailed brain dissections.

Vesalius debunked Galen's "pneuma" theory through direct observation, noting the absence of any vital spirits or "network of nerves" in the brain. Although he could not explain how the brain functioned, he provided the first accurate anatomical representation of the brain's structure.

The Enlightenment: Electricity and Brain Function

The Enlightenment ushered in a new era of brain research, influenced by the discovery of electricity. Luigi Galvani, an Italian scientist, demonstrated that electrical currents could trigger muscle movement in animals, suggesting that the brain might generate a bioelectric signal controlling bodily functions. This marked a shift from mystical explanations to a more mechanistic understanding of brain function.

During this period, phrenology also emerged—a now-debunked theory suggesting that a person's skull shape reflected their intelligence and personality. While phrenology was flawed, it introduced the idea of brain localization, where specific brain regions might govern specific functions.

19th Century: Scientific Maturity and Brain Localization

By the 19th century, brain science began to mature. French physician Paul Broca discovered that damage to a specific area in the left hemisphere, later named Broca's area, led to speech impairments, while Carl Wernicke identified a different area affecting language comprehension (Wernicke's area). These discoveries further supported the idea that brain functions were localized.

20th Century: Neuron Theory and Electrical Networks

The 20th century marked the emergence of modern neuroscience. Santiago Ramón y Cajal, a Spanish neuroscientist, used staining techniques to reveal that the brain was composed of individual neurons connected in complex networks. He described the brain using the metaphor of a "telegraph system," where neurons transmitted electrical signals across the brain.

Further progress was made when British scientists Alan Hodgkin and Andrew Huxley studied nerve impulses using squid axons, leading to a groundbreaking mathematical model explaining how neurons generate and transmit electrical signals.

Key Milestones of Brain Science Research

1. Mystical Phase (Ancient Greece - 16th century):

   • Aristotle believed the heart governed emotions.

   • Galen introduced the "pneuma" theory and brain centrality.

2. Renaissance (16th century):

   • Vesalius disproved Galen's theory and provided anatomical accuracy.

3. Enlightenment (18th century):

   • Galvani discovered bioelectricity's role in muscle movement.

   • Phrenology introduced the concept of brain localization.

4. 19th Century:

   • Broca and Wernicke identified brain regions responsible for speech and comprehension.

5. 20th Century:

   • Cajal described neurons and their complex connections.

   • Hodgkin and Huxley mathematically modeled nerve impulses.