The Theory of Cognitive Modes

A new understanding of thinking and behavior

Sperry, Jenkins: Left Brain, Right Brain

A noted scientist and a wounded veteran: roots of the left/right brain story

First of three monthly parts

The left brain/right brain story has permeated our culture. It is common to hear someone comment that they are a “left-brain” or a “right brain” person, and it is just as common to hear about left- or right-brain thinking. The left brain/right brain story apparently began on a day in February 1962, when a 48-year-old man with intractable epilepsy was brought into an operating room at White Memorial Medical Center in Los Angeles. This was the moment that Roger Sperry, a world-renowned neuroscientist, had long awaited.

For years, Sperry and his colleagues at the California Institute of Technology had surgically separated the left and right sides (also called hemispheres because each is, roughly, half a sphere) of the brains of cats and monkeys, and then tested the animals in experiments that measured cognitive function. He and his team had developed a novel way to plumb the mysteries of the living mammalian brain—and their conclusions from this so-called split-brain research with animals had taken the neuroscientific world by storm.

“They perceive, learn, and remember much as normal animals do,” Sperry wrote, in a paper that attracted significant attention inside academia but went virtually unnoticed in the larger world. “However, if one studies such a ‘split-brain’ monkey more carefully...one finds that each of the divided hemispheres now has its independent mental sphere or cognitive system....In these respects, it is as if the animals had two separate brains.”1

On that winter day in 1962, Sperry was setting the stage for his first test on a human, William Jenkins.

Mr. Jenkins was a military veteran who had suffered grand mal seizures (“brain spasms” that produce massive convulsions)—sometimes as many as 10 a day—since surviving a bomb explosion near the end of World War II. He had learned of a radical operation, a version of which had been performed by other doctors two decades before at a Rochester, New York, hospital, that had relieved the symptoms of extreme epilepsy. He was eager for the California surgeons to try it on him. Unlike patients who underwent earlier versions of this operation, Mr. Jenkins made a deal with his doctors: Whether or not the surgery reduced his suffering, he agreed to work with Sperry, who would administer postoperative behavioral tests similar in principle to those given to the scientist’s experimental animals. Assuming that Mr. Jenkins’s higher cognitive functioning survived the surgery, his ability to respond on command and communicate with speech might give Sperry a quantum boost in his research.

“Even if it doesn’t help my seizures,” Mr. Jenkins said before meeting the scalpel, “if you learn something, it will be more worthwhile than anything I’ve been able to do for years.”

The surgeons shaved Mr. Jenkins’s head, sterilized and peeled back his scalp, opened two holes into his skull, and began the meticulous work of cutting the corpus callosum, the largest structure that connects the left and right hemispheres of the brains of humans; this structure consists of some 250 million nerve fibers, an impressive piece of brain anatomy. The operation went according to plan and Mr. Jenkins recovered without incident; his convulsions were indeed gone, and, like Sperry’s monkeys and cats, on casual observation he seemed cognitively normal.

But Sperry’s testing revealed that such causal observations were misleading. Mr. Jenkins’ cognition was indeed changed, and the hemispheres were indeed revealed to have some distinct capabilities. What are those capabilities, and how do they align with the popular left brain/right brain narrative?

In our next post, in May, we'll explain.

Stephen M. Kosslyn, Ph.D., is a psychologist and neuroscientist, and G. Wayne Miller is an author.

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