The Theory of Cognitive Modes

A new understanding of thinking and behavior

Left Brain, Right Brain: Two Sides, Always Working Together

Part 2 of a 3-part detailed look at the left brain/right brain story.

Second of three monthly parts.

Researchers have known for decades that none of the sweeping assertions in the popular press about left brain/right brain differences are supported by solid science. (Roger Sperry, whose work unintentionally begin the pop-culture mythos, himself noted this… though his caveats were not widely heeded. More in part one of this thread.)

For example, the left hemisphere is often described as verbal and the right as perceptual—but this distinction doesn’t hold up as a generalization. In reality, both hemispheres typically contribute to both sorts of activities—but do so, often subtly, in different ways.

Consider language: Typically, the left hemisphere produces correct word order—to say, for instance, “I have two left feet” instead of “I two left feet have.” (Yoda’s fractured English may indicate that his alien brain didn’t include a human-standard left hemisphere.) But the right hemisphere also is crucial in language: It extracts the implied meaning—that the speaker doesn’t literally have two left feet but has trouble with physical coordination, much as a person would if she were cursed with actually having two feet shaped like the left one (each with the big toe on the right and the smallest toe on the far left).

And although it is true that the left hemisphere controls speech and plays a major role in grammar and comprehension, the right hemisphere plays a key role not only in our comprehending implied meaning but also in our understanding and producing verbal metaphors and humor, and it is largely responsible for helping us to decipher the meaning of changes in speaking tone, such as the rising tone at the end of a spoken question. And both hemispheres play critical roles in extracting meaning in general. Indeed, neuroimaging studies have conclusively shown that many aspects of language processing are distributed over both hemispheres.

Similarly, consider perception: For example, if you look at a house, the left hemisphere will allow you to register the shapes of the doors, windows, and other parts, while the right will allow you to take in the overall contours of the building. At the same time, the left hemisphere will specify the relative locations of the parts in terms of categories, such as “the window is left of the front door,” while the right hemisphere will specify locations in terms of specific distances, such as by indicating the precise distance the window is from the door. Again, brain imaging studies have conclusively shown that many aspects of perceptual processing are distributed over both hemispheres.

The sorts of documented differences between left-brain and right-brain functioning are hardly the stuff of popular generalizations, but they are fundamentally important to a genuine understanding of brain functioning. The fine print matters.

The larger issue is not just that people are being classified as “right-brained” or “left-brained” by so-called experts. It’s that the hemispheres are being classified in terms of simple overreaching dichotomies—such as the left’s being verbal, analytic, and logical, and the right’s being perceptual, intuitive, and emotional. It just doesn’t work that way.

Another fundamental flaw of the left/right story is that each of the specialized brain areas does not work alone but rather works as part of a system that includes many other brain areas—including areas on the opposite side of the brain.

To understand language fully, for example, you need to understand the grammar (which dictates the structure of sentences, which is better accomplished by the left hemisphere), the meaning of changes in tone (which is better accomplished by the right hemisphere), and how meaning is deciphered (which is accomplished by both hemispheres working together). In other words, the two hemispheres are part of a single system. A computer is a good example of a system: It has keyboard, active memory (“RAM”), a hard disk (or solid state storage system) for retaining information over time, a screen, speakers, and so on. All of the parts are designed to work together to accomplish specific goals (allowing you to write, to play music, and so on). No one part alone would accomplish much; the power of the system lies in how the parts all work together. The same is true of the brain.

So the hemispheres do differ, but at a more specific and detailed level than is claimed in the popular press and on the Internet. One half-brain is not “logical” and the other “intuitive,” nor is one more “analytical” and the other more “creative.” Both halves play important roles in logical and intuitive thinking, in analytical and creative thinking, and so forth. All of the popular distinctions involve complex functions, which are accomplished by multiple processes—some of which may operate better in the left hemisphere and some of which may operate better in the right hemisphere—but the overall functions cannot be said to be entirely the province of one or the other hemisphere.

And far from having separate lives, the two halves work together. They are not isolated systems that compete or engage in some kind of cerebral tug-of-war; one is not an undisciplined child, the other a spoilsport that throws schoolyard tantrums. Rather, as we have stressed, the brain is a single, marvelously complicated, and deeply integrated system. Like those of a well-maintained bicycle, the parts of the brain do have different functions—but, like the parts of a bike, they are designed to work together.

Finally, as we discussed earlier, there is solid evidence that none of us relies primarily on one or the other hemisphere. We all use all of our brains; none of us are truly “left-brained” or “right-brained.”

In our next post, in June, we'll trace the media coverage that led to establishment of a myth.

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

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