Left Brain, Right Brain? Wrong

If you doubt that the left brain/right brain theory of personality is widespread, try Googling it sometime. You’ll get millions of hits: books you can read, videos you can watch, tests you can take, advice from (supposed) experts you can follow, courses you can take, and so on. The idea that the left side is “logical and analytical” and the right is “intuitive and creative” seems to be natural law.

In fact, it may be the poster child for pseudoscience—something that looks like science but isn’t.

Neuroscientists have known for a long time that research does not support such sweeping claims about how people differ in their left and right sides, or hemispheres. The functions of the hemispheres are in fact different, but these differences aren’t what the popular culture holds to be true—the differences lie in how each side processes very specific kinds of information. Example: The left hemisphere processes details of visible objects whereas the right processes overall shape. The left hemisphere plays a major role in grammar and decoding literal meaning whereas the right plays a role in understanding verbal metaphors and decoding indirect or implied meaning. And so forth. Hardly the sort of stuff that can guide your life!

The left/right story has its roots in a series of 16 operations in the 1960s and 1970s conducted by surgeons working with Roger W. Sperry, a neuroscientist at the California Institute of Technology. The doctors sought relief for very sick epileptics by cutting the corpus callosum, the largest structure connecting the left and right hemispheres. The epileptics did find relief—and in studying them after their operations, Sperry confirmed cognitive differences between the two sides and then disclosed his findings in the research literature. Word reached the mainstream culture, and newspapers and magazines began to pay attention.

The New York Times Magazine in 1973 published an article, "We Are Left-Brained or Right-Brained," that began: “Two very different persons inhabit our heads, residing in the left and right hemispheres of our brains, the twin shells that cover the central brain stem. One of them is verbal, analytic, dominant. The other is artistic…” Two years later, Time magazine featured the left/right story. In 1976, Harvard Business Review published “Planning on the Left Side and Managing on the Right” and the following year, it was Psychology Today’s turn to trumpet the idea. The 1981 Nobel Prize in Physiology or Medicine that Sperry received for his split-brain research opened the floodgates.

The popular narrative about the left brain versus the right brain has several major flaws. As we have noted, the functions of the two sides of the brain have been mischaracterized. But more than that, the two sides of the brain always work together. And, crucially, people don’t have a “dominant” left or right hemisphere. We don’t think primarily with one part of our brain, which may be in a tug-of-war with other parts.

Within science, warnings against over-interpretation of Sperry’s results were sounded even before he won the Nobel Prize by Brenda Milner, of the Montreal Neurological Institute, and Stevan Harnad, founder of the journal Behavioral and Brain Sciences, among others. Sperry himself warned that “experimentally observed polarity in right-left cognitive style is an idea in general with which it is very easy to run wild… it is important to remember that the two hemispheres in the normal intact brain tend regularly to function closely together as a unit” in an essay published in the journal Neuropsychologia 30 years ago.

But warnings from scientific circles published in small-circulation research publications do not always reach the wider culture (consider, as but one example, the many warnings about the dangers of smoking that scientists issued for years before the 1964 Surgeon General’s report finally got the public’s attention). And even if such warnings were circulated widely, they may not have been heeded. It’s sometimes difficult to override the power of a simple and seemingly logical narrative that offered answers in the age-old quest for understanding ourselves and others—and also practical applications for everyday life. The advent of the Internet with its power to reach and inform—and misinform—essentially canonized the left/right story. As an aside, we would note that because of its complexity, the brain in general is susceptible to myths. Other popular examples include the claim that we use just 10 percent of our brains (actually, every region of a healthy brain is used, as brain scanning demonstrates) and that even moderate amounts of alcohol kill neurons (excessive drinking can, however, damage another important brain structure, dendrites).

You can read more about the origins and growth of the left brain/right brain story in our book, Top Brain, Bottom Brain: Surprising Insights About How You Think.

By now, you may be wondering about our Theory of Cognitive Modes, which relies on an anatomical division of the brain, but not the one that divides it into left and right sides. Did we fall into the same trap? We’ll explain why we did not—and cite some of the credible scientific research on which it rests—in our next post.

Meanwhile, to determine which of the four cognitive modes described in our theory best characterizes you, you can take our online quiz.