Monday, December 3, 2007

Left-Brain/Right-Brain: Wrong-Minded

There’s no shortage of left-brain/right-brain propaganda in pop culture. Browse the shelves at your local bookstore and you’ll find titles like Daniel Pink’s A Whole New Mind: Why Right-Brainers Will Rule the Future; peruse the booming educational toy market and you’ll find products like Brainy Baby’s “Left Brain” and “Right Brain” DVDs; or just open your ears to the ramblings of a motivational speaker or the chit chat of the office break room, and you’re likely hear some reference to left- and right-brain tendencies. In fact, a quick Google search turns up tens of thousands of documents touting the concept’s usefulness for everything from improving elementary school education or business management strategies, to understanding biblical symbolism, or why men are, and I quote, “beer-guzzling, TV-glued, [and] sex-driven.” You can even test your own left-brain/right-brain tendencies with a multitude of online personality tests. But don’t waste your clicks: if you tend to focus on artistic/holistic/spatial aspects of things you will be labeled “right-brained,” whereas if you lean towards logical/detail-oriented/sequential features, you are “left-brained.” Given its pervasiveness, you may be surprised to learn that most cognitive neuroscientists – scientists who study the relation between mind and brain – cringe when they hear popular references to left- versus right-brain function. To us, hearing someone say, “let’s learn to think with our right hemispheres…” is about as stimulating as fingernails on a chalkboard.

But, you say, isn’t it true that the brain is divided into two hemispheres? Yes it is. And isn’t it the case that the two sides are not identical in function? Yes, of course. Then what’s the problem with all this left-brain/right-brain stuff? Well, let me illustrate by example. Suppose I told you I could read your personality strengths and weaknesses – your self esteem, cautiousness, wit, secretiveness, destructiveness, and so on – simply by measuring the bumps and indentations on your skull. Perhaps you’d be interested in me examining your fiancée (or wish I had before you tied the knot), but more likely you’d think I was blowing smoke. And you’d be right. What I’ve described, in fact, is the 19th century doctrine of phrenology, which held that different brain areas controlled different personality traits, which could be more or less developed. A well-developed trait would command more neural bulk and therefore press on the skull to produce a measurable bump on the head; vise versa for under-developed traits. As ridiculous as it sounds today, phrenology was all the rage in 19th century popular culture, even making its way into political, management, and yes, marriage decisions.

What’s interesting, though, is that while the application of phrenology was seriously misguided, the underlying science was quite legitimate, even accurate in important respects. Indeed, just replace self-esteem, cautiousness, and wit, with motor control, speech, and memory and suddenly phrenology doesn’t seem so ridiculous (well except for that bump-on-the-head thing, but that’s not the core of the theory). In fact, that is precisely what many scientists of the time did with the idea: they ran with the fundamental concept, and ditched the personality trait lunacy.

So what does phrenology have to do with the current left-brain/right-brain mentality? In short, everything. Just like phrenology, the left-right craze is based on a fundamental scientific observation, namely that the two hemispheres are not identical in function, and just like phrenology, the concept has been seriously overblown and misapplied. The fact is, with few exceptions, just about any function or ability you can imagine involves a host of coordinated brain circuits in both hemispheres. The two sides may make somewhat different contributions to these abilities, but these differences generally pale in comparison to differences in function we see between networks within the hemispheres, such as those networks that support visual recognition versus those that enable language comprehension.

The parallels between popular left-brain/right brain dichotomies and phrenology run even deeper, though, as both concepts are based on a more fundamental misconception about brain organization, namely that complex functions are carried out by circumscribed islands of brain tissue. Look at just about any map of brain function and you will find tidy parcellations, like cuts of beef, with labels such as “language,” “memory,” “vision,” and “thought.” But this drastically oversimplifies the picture. For example, there is no “language area.” Instead our ability to use language is supported by a coordinated and widely distributed network of circuits spanning many regions in both hemispheres. These circuits may be individually specialized in function, to be sure, but it is the integrated action of the network that gives rise to our capacity for language. Furthermore, some of these circuits are not slaves to a linguistic taskmaster, but participate in other abilities as well. The same holds true of other functions.

So to say that the left-brain does one thing, and the right-brain does another, is a throw-back to phrenology (and a clumsy one at that!), that fails to recognize the more dynamic, interactive, network-based organization of brain function. So get with the network. Left-brain/right-brain is so 19th century!

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