Ways of seeing the brain inspire notions of how it works

As scientists have developed more sophisticated methods and ideas, their understanding of how the brain works has shifted too.

Alex Huth, James Gao and Jack Gallant/UC Berkeley

The mysterious contents of the skull have long captivated their owners.

Ancient Egyptians treated brain injuries by pouring milk in both ears. Aristotle believed the brain was a cooling unit for the heart. Galen, the leading physician of the Roman Empire, claimed that “animal spirits” imbued the brain with its abilities.

These ideas were a product of limited tools and unscientific preconceptions. As scientists have developed more sophisticated methods and ideas, their understanding of how the brain works has shifted too.

ANATOMY LESSON In the 1500s, Flemish anatomist Andreas Vesalius began studying the anatomy of corpses. His detailed, lifelike representations, many published in 1543 in De Humani Corporis Fabrica, led scientists to question some antiquated ideas about how the human brain works and what makes it unique. Vesalius was skeptical of the notion that nerves are conduits for “animal spirits,” and showed that people have fluid-filled ventricles proportionate in size to those of animals. Earlier thinkers had proposed that outsized ventricles gave human brains their exceptional power. The Granger Collection, NYC

JOLT OF INSPIRATION In experiments during the 1780s that inspired Mary Shelley’s 1818 novel Frankenstein, Luigi Galvani hooked up a long metal wire to recently deceased frogs during a lightning storm and watched as each strike caused the frogs’ legs to twitch. Electricity was the mysterious “animal spirit” that carried the impulse for muscle contraction, Galvani concluded. His results gave birth to the field of neurophysiology, in which scientists study nerve cells’ electrical communication. The Granger Collection, NYC

NEURONS IN BLACK AND WHITE Aided by a black stain that could highlight individual neurons and a masterful drawing hand, the Spanish researcher Santiago Ramón y Cajal ushered in modern neuroscience in the late 1800s. His exquisite renderings of complex and diverse neurons showed that instead of being a tangled nest of fused fibers, the nervous system is an intricately connected network of discrete nerve cells, a claim called the neuron doctrine. From his drawings, Cajal correctly guessed that nerve impulses travel directionally along cellular tendrils to send messages to adjacent cells. Instituto Cajal/Wikimedia Commons

FORM TO FUNCTION Over the years, rare brain injuries have offered scientists a way to link specific cognitive powers to certain brain regions. After a tamping iron blasted through the front part of his brain (shown) in 1848, the mild-mannered rail worker Phineas Gage turned nasty. His dramatic change in character told scientists that the damaged part of the brain was important for personality. Other famous cases, such as the patient of 19th century French physician Pierre Paul Broca who was unable to speak any word other than “tan,” and the 20th century patient known by the initials H.M., who lost his memory after a surgery, also provided rare glimpses into the geography of brain function. John Darrell Van Horn/UCLA Laboratory of Neuro Imaging

ELECTRICAL TRACES Since Galvani’s jumping frogs, scientists have made leaps in understanding electrical signals in the brain. In the late 1950s, electrodes recorded single neurons in anesthetized animals as they responded to particular visual inputs. Later, scientists were able to record electrical activity from awake animals. Electrical activity ensconced in a skull is now detectable by electrodes placed on the head using a method called electroencephalography, or EEG (shown). M. Javidan/ Epilepsy Research and Treatment 2012

THE BRAIN AT WORK Toward the end of the 20th century, researchers finally developed methods that allowed them to visualize brain activity as it happened. In the 1970s, researchers developed the first positron emission tomography scanner, a machine that could track molecular activity in the brain using radioactive probes. Scientists later began to use magnetic resonance imaging, or MRI (shown), to produce detailed images of the brain’s anatomy, connections and behavior. The technology has produced insights into how different parts of the brain work together to produce thoughts, memories, emotions and other mental experiences. Alex Huth, James Gao and Jack Gallant/UC Berkeley

Laura Sanders is the neuroscience writer. She holds a Ph.D. in molecular biology from the University of Southern California.

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