A Neurotech History Series

By the late nineteenth century, many scientists believed the brain formed one continuous network.

Using Golgi’s staining technique, Santiago Ramón y Cajal carefully examined nervous tissue and concluded that the brain is built from individual neurons separated by tiny gaps. He proposed the neuron doctrine, one of the foundational principles of neuroscience.

His work transformed our understanding of how information flows through the nervous system.

Every modern model of neural circuits and brain function builds on Cajal’s insight.

A Neurotech History Series

Looking through a microscope, the brain once appeared as an indistinct mass of tangled tissue. Scientists could see cells, but not how individual neurons were organized or connected.

In 1873, Italian physician and scientist Camillo Golgi transformed neuroscience by developing the Black Reaction (la reazione nera), a silver chromate staining technique that randomly stained only a small number of neurons. Because just a few cells were coloured while their neighbours remained transparent, each stained neuron could be seen in its entirety—its cell body, branching dendrites, and long axon. For the first time, researchers could appreciate the extraordinary complexity and diversity of individual neurons.

One laboratory technique opened an entirely new window into the brain’s architecture, laying the foundation for modern neuroscience.

Golgi’s method also enabled Santiago Ramón y Cajal to demonstrate that the brain is composed of individual neurons rather than a continuous network, establishing the neuron doctrine that underpins modern neuroscience.

A Neurotech History Series

For centuries, the surface of the brain appeared uniform. Scientists knew brain injuries could change behaviour, but they had little idea whether different regions served different functions.

German physicians Gustav Fritsch and Eduard Hitzig applied tiny electrical currents to different locations on the cerebral cortex of dogs. Stimulating one area moved a leg, while stimulating another produced movements of the face, neck, or forelimb.

Their experiments provided the first clear evidence that the cerebral cortex is functionally organized. Different regions are responsible for different movements.

This principle underpins modern neurosurgery, transcranial magnetic stimulation, deep brain stimulation, and brain-computer interfaces.

A Neurotech History Series

Early nineteenth-century scientists knew that nerves connected the brain and spinal cord to the body, but they did not understand how information travelled. Did the same nerve carry messages in both directions?

Working independently, Charles Bell and François Magendie showed that the nerve roots entering the back of the spinal cord carry sensory information to the brain, while the roots leaving the front carry motor commands to the muscles.

The Bell–Magendie law revealed that the nervous system is organized rather than chaotic. Sensation and movement follow distinct pathways, allowing the brain to receive information from the outside world while sending precise instructions back to the body.

Physicians still rely on this principle to diagnose neurological disorders, and it continues to inform modern neurotechnology, from spinal cord stimulation to brain-computer interfaces.

A Neurotech History Series

At the end of the eighteenth century, scientists could observe electricity in lightning and static sparks, but they had no reliable way to produce it. Without a steady source of electrical current, experiments on the nervous system were difficult and often impossible.

Italian physicist Alessandro Volta investigated whether electricity originated in living tissue or from the metals used in experiments. While testing different combinations of metals, he stacked alternating discs of zinc and copper separated by cloth soaked in salt water and created the voltaic pile—the world’s first practical battery.

For the first time, scientists had a dependable source of electricity that could be used repeatedly in the laboratory. This transformed research not only in physics but also in physiology, allowing investigators to study nerves and muscles with unprecedented precision.

Modern neurotechnology still depends on the ability to generate controlled electrical currents. From laboratory stimulators to deep brain stimulation and cochlear implants, the lineage can be traced back to Volta’s simple stack of metal discs.

A Neurotech History Series

While dissecting frogs in the 1780s, Italian physician Luigi Galvani noticed something extraordinary. A dead frog’s leg suddenly twitched when a metal instrument touched an exposed nerve. The animal was no longer alive, yet its muscles contracted as if they had received a command from the brain.

At the time, no one understood how the brain communicated with the body. Many scientists believed nerves carried invisible fluids or “animal spirits.” Galvani wondered whether the twitching revealed something entirely different: that the nervous system generated its own form of electricity. He called it animal electricity.

Galvani’s interpretation would later be debated, but his experiments transformed science. They shifted the study of the nervous system from speculation toward measurable electrical phenomena and inspired a generation of researchers to investigate how nerves and muscles function.

Today we know that neurons communicate through tiny electrical signals created by the movement of charged ions across their membranes. Every major neurotechnology—from EEG and deep brain stimulation to transcranial magnetic stimulation and brain-computer interfaces—rests on the same fundamental insight that Galvani’s twitching frog helped uncover: the nervous system is electrical.