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1.- THERE IS NO LEFT-BRAIN/RIGHT-BRAIN DIVIDE

jose-kevo-3 You are hardly alone if you believe that humanity is divided into two great camps: the left-brain and the right-brain thinkers — those who are logical and analytical vs. those who are intuitive and creative. For years, an industry of books, tests and videos has flourished on this concept. It seems to be natural law.

Except, it isn’t.

Scientists have long known that the popular left-brain/right-brain story doesn’t hold water. Here’s why. First, the sweeping characterizations of what the two halves of the brain miss the mark: one is not logical and the other intuitive, one analytical and the other creative. The left and right halves of the brain do function in some different ways, but these differences are more subtle than is popularly believed (for example, the left side processes small details of things you see, the right processes the overall shape). Second, the halves of the brain don’t work in isolation; rather, they always work together as a system. Your head is not an arena for some never-ending competition, the brain’s “strong” side tussling with its “weak.” Finally, people don’t preferentially use one side or the other.

The roots of the left/right story lie in a small series of operations in the 1960s and 1970s by doctors working with Roger W. Sperry, a Nobel-laureate neuroscientist at the California Institute of Technology. Seeking treatment for severe epilepsy, 16 patients agreed to let the doctors cut the corpus callosum, the main nerve bundle that joins the two halves of the brain. They found some relief from these dramatic visits to the O.R. — and when they left the hospital, they allowed Sperry and his team to study their cognitive functioning.

Laboratory findings do not always make their way into the popular culture, but these did, which provided an unfortunate opportunity for misinterpretation of what was, in essence, a limited set of experiments. In 1973, the New York Times Magazine published an article titled, “We are left-brained or right-brained,” which began: “Two very different persons inhabit our heads … One of them is verbal, analytic, dominant. The other is artistic …” TIME featured the left/right story two years later. Harvard Business Review and Psychology Today jumped in. Never mind that Sperry himself cautioned that “experimentally observed polarity in right-left cognitive style is an idea in general with which it is very easy to run wild.” A myth spread.

Myths, of course, are a timeless way to make sense of experience. In the search for meaning, people may create simplified narratives. This is a reasonable strategy, but the right-brain/left-brain narrative introduced misconceptions.

We have developed a new theory built on another, frequently overlooked, anatomical division of the brain: into its top and bottom parts. Among other things, the top part sets up plans and revises those plans when expected events do not occur; the bottom classifies and interprets what we perceive.

Based on decades of research, the theory holds that this distinction can help explain why individuals vary in how they think and behave. We all use both parts of the brain, but differ in how deeply we may use each part. The key is the way the parts interact, not each part by itself. Depending on the extent to which a person uses the top and bottom parts, four possible cognitive modes emerge. These modes reflect the amount that a person likes to devise complex and detailed plans and likes to understand events in depth. (You can determine your own dominant mode with this test.)

This new approach avoids the pitfalls of the left-brain/right-brain story for several reasons. The characterizations of what each part does are based on years of solid research. We emphasize that the two parts always work together — it’s the relative balance of how much people use the two parts that determines each cognitive mode. And we stress that the parts of the brain don’t work alone or in competition, but seamlessly together. In some ways this theory too is a simplification, but one that brings more understanding. If there’s one thing we do know, it’s that as a species, we are continually inclined to try to understand what we encounter, even something as complex as the brain.

Kosslyn is a cognitive neuroscientist and was professor of psychology at Harvard University for over 30 years; he now serves as the founding dean of the Minerva Schools at the Keck Graduate Institute. Miller is an author, filmmaker and Providence Journal staff writer. They are the co-authors of Top Brain, Bottom Brain: Surprising Insights Into How You Think.