Phrenology and the Localization Debate

Bumps on the skull, ablated pigeons and electrified dog brains: how the 19th century argued over whether different parts of the brain do different jobs.

Does the brain work as one undivided whole, or do different parts do different things? This was one of the great scientific debates of the 19th century.

Gall's phrenology

The Viennese physician Franz Joseph Gall (1758–1828) proposed that the brain is a collection of "organs", each responsible for a mental faculty — from language and memory to "benevolence", "combativeness" and "love of offspring". A stronger faculty, he claimed, meant a bigger organ, which pushed out the skull above it. With his collaborator Johann Spurzheim, the idea became phrenology, and skull-reading became a popular craze across Europe and America.

Phrenology was pseudoscience: skull shape doesn't reflect the brain beneath it, and the "faculties" were invented categories. It was also used to justify racist and sexist claims. Yet Gall was a skilled anatomist, and his central intuition — functional localisation — would prove important.

Flourens and the whole brain

The French physiologist Pierre Flourens tested Gall by removing parts of the brains of pigeons and other animals in the 1820s. He found that removing the cerebellum disrupted coordination and that the brainstem was vital, but that damage to the cerebral hemispheres seemed to reduce all functions together. He concluded that the cortex acts as a whole — a view called equipotentiality.

The evidence for localisation

Two lines of evidence swung the debate. In 1861 Paul Broca showed that damage to a specific area of the left frontal lobe destroyed the ability to speak. And in 1870 the German physicians Gustav Fritsch and Eduard Hitzig applied weak electric currents to the cortex of dogs and produced movements of specific body parts — revealing the motor cortex. The modern view combines both sides: specialised regions exist, but complex abilities rely on networks spanning many of them.