First Primate Brain Map, circa 1917

Scale drawing of the left hemisphere of one of Leyton’s and Sherrington’s experiments on a gorilla showing which areas correspond with movements of which parts of the body.
Courtesy of the Journal of Experimental Physiology

At the turn of the 20th century, British physiologists Charles Scott Sherrington and Albert Sidney Frankau Leyton started poking around in the brains of anesthetized great apes in their lab at the University of Liverpool to see what would happen. While their work would never secure the necessary permits in any laboratory today, the data they generated is in every modern neurobiology textbook, albeit in simplified form.

The researchers examined the brains of 22 chimpanzees, three orangutans, three gorillas, and a handful of other animals under deep anesthesia induced by chloroform and ether. Applying mild electrical stimulation to the cortex, they revealed that the control of certain body parts...

“There had been a lot of arguments about whether functions are localized,” says Roger Lemon, a neurophysiologist at University College London. While cortical stimulation had been shown to elicit motor responses in dogs and rabbits, “there were people who were saying it’s not possible to get these same effects in primate brains.”

Sherrington and Leyton evoked cortical responses that were quite complex, sometimes including several consecutive movements. In all, they documented 400 different “first movements”—the initial motor response to a given stimulus—and charted the most complex motor map ever created, published in the Quarterly Journal of Experimental Physiology in 1917. “The paper is famous for the fact that it represents the first systematic mapping of the primate brain,” says Lemon. “It was a very big step forward.”

The figure shown here is a simplified map of the cortex that summarizes the evoked movements into broad categories of body area. Stimulation to the area labeled “leg,” for example, would result in a variety of leg movements depending on the exact location of the electrode.

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