In your right mind

Another peculiarity of the human brain is lateralization, which is the tendency of the brain to have a dominant side.  It's most clearly reflected in hand dominance; because of the cross-wiring of the brain, people who are right-handed have a tendency to be left brain dominant, and vice versa.  (There's more to it than that, as some people who are right handed are, for example, left eye dominant, but handedness is the most familiar manifestation of brain lateralization.)

It bears mention at this juncture that the common folk wisdom that brain lateralization has an influence on your personality -- that, for instance, left brain dominant people are sequential, mathematical, and logical, and right brain dominant people are creative, artistic, and holistic -- is complete nonsense.  That myth has been around for a long while, and has been roundly debunked, but still persists for some reason.

I first was introduced to the concept of brain dominance when I was in eighth grade.  I was having some difficulty reading, and my English teacher, Mrs. Gates, told me she thought I was mixed-brain dominant -- that I didn't have a strongly lateralized brain -- and that this often lead to processing disorders like dyslexia.  (She was right, but they still don't know why that connection exists.)  It made sense.  When I was in kindergarten, I switched back and forth between writing with my right and left hand about five times until my teacher got fed up and told me to simmer down and pick one.  I picked my right hand, and have stuck with it ever since, but I still have a lot of lefty characteristics.  I tend to pick up a drinking glass with my left hand, and I'm strongly left eye dominant, for example.

Anyhow, Mrs. Gates identified my mixed-brainness, and the outcome apropos of my reading facility, but she also told me that there was one thing that mixed-brain people can learn faster than anyone else.  Because of our nearly-equal control from both sides of the brain, we can do a cool thing, which Mrs. Gates taught me and I learned in fifteen seconds flat.  I can write, in cursive, forward with my right hand while I'm writing the same thing backwards with my left.  (Because it's me, they're both pretty illegible, but it's still kind of a fun party trick.)

[image courtesy of the Wikimedia Commons]

Fast forward to today.  Some recent research has begun to elucidate the evolutionary reasons behind lateralization.  It's been known for years that lots of animals are lateralized, so it stands to reason that it must confer some kind of evolutionary advantage, but what that might be was unclear... until now.

Research by a team led by Onur Güntürkün, of the Institute of Cognitive Neuroscience at Ruhr-University Bochum, in Germany, has looked at lateralization in animals from cockatoos to zebra fish to humans, and has described the possible evolutionary rationale for having a dominant side of the brain.

"What you do with your hands is a miracle of biological evolution," Güntürkün says.  "We are the master of our hands, and by funneling this training to one hemisphere of our brains, we can become more proficient at that kind of dexterity.  Natural selection likely provided an advantage that resulted in a proportion of the population -- about 10% -- favoring the opposite hand. The thing that connects the two is parallel processing, which enables us to do two things that use different parts of the brain at the same time."

Additionally, Güntürkün says, our perceptual systems have also evolved that kind of division of labor.  Both left and right brain have visual recognition centers, but in humans the one on the right side is more devoted to image recognition, and the one on the left to word and symbol recognition.  And this is apparently a very old evolutionary innovation, long predating our use of language; even pigeons have a split perceptual function between the two sides of the brain (and therefore between their eyes).  They tend to tilt their heads so their left eye is scanning the ground for food while their right one scans the sky for predators.

So what might seem to be a bad idea -- ceding more control to one side of the brain than the other, making one hand more nimble than the other --turns out to have a distinct advantage.  And if you'll indulge me in a little bit of linguistics geekery, for good measure, even our word "dexterous" reflects this phenomenon.  "Dexter" is Latin for "right," and reflects the commonness of right-handers, who were considered to be more skillful.  (And when you find out that the Latin word for "left" is "sinister," you get a rather unfortunate lens into attitudes toward southpaws.)

Anyhow, there you have it; another interesting feature of our brain physiology explained, and one that has a lot of potential for increasing our understanding of neural development.  "Studying asymmetry can provide the most basic blueprints for how the brain is organized," Güntürkün says.  "It gives us an unprecedented window into the wiring of the early, developing brain that ultimately determines the fate of the adult brain.  Because asymmetry is not limited to human brains, a number of animal models have emerged that can help unravel both the genetic and epigenetic foundations for the phenomenon of lateralization."

Thinking with both sides of the brain

One of the reasons I love science is that it challenges our preconceived notions about the way the world works.

We are data-gatherers and pattern-noticers, we humans.  Even as babies we are watching and learning, and trying to make generalizations about the world based on what we've experienced.  And while many of those generalizations turn out to be correct -- we wouldn't have lasted long as a species if they weren't -- we sometimes draw incorrect conclusions.

And when we do, we tend to hang onto them like grim death.  Once people have settled on a model, for whatever reason -- be it that "it seems like common sense" or that it has gained currency as some kind of "urban legend" -- it becomes extremely hard to undo, even when the science is unequivocal that our beliefs are wrong.

I ran across a particularly good example of that this week.  I teach an introductory neurology class, and when we start talking about brain physiology and its role in personality, inevitably someone brings up the phenomenon of brain lateralization -- the fact that, as we develop, one side of the brain exerts more influence over us physically than the other does.  This is why most of us have a dominant hand, foot, eye, and so forth.

Most common biological traits can be explained based upon some kind of evolutionary advantage they provide, but the jury's still out on this one.  Halpern et al. concluded, in 2005 in The Journal of Neuroscience, in their paper "Lateralization of the Vertebrate Brain: Taking the Side of Model Systems," that the evolutionary advantage of allowing one side of the brain to dominate the motor activity of the body is that it allows the other, non-dominant side to do other things -- something they call "parallel processing."  But even they admitted that this was speculation.

One claim that gained a lot of currency, beginning in the 1960s, was that people who were right brain dominant were artistic, creative, and saw things holistically, and that people who were left brain dominant were logical, verbal, mathematical, and sequential.

Now, there may be some truth to the claim that the sensory-processing centers on the two sides of the brain do see the word differently -- studies done on people who have had strokes in the cerebrum, and those with "split brains" (who have had the corpus callosum cut, preventing cross-talk between the two cerebral hemispheres), do seem to support that there is a dramatic difference in how the two sides of the brain interpret what you see.   (For an amazing personal account that supports this view, check out Jill Bolte Taylor's talk "A Stroke of Insight.")

The idea that people with intact brains are either artistic right-brainers or logical left-brainers has led to a whole slew of "therapies" meant to allow people to "balance their brains."  It has been especially targeted at the left-brainers, who are sometimes seen as cold and calculating.

Many of these treatments require such things as forcing people to write or perform actions with their non-dominant hands, or patching their dominant eye -- the claim being that this will force the poor, subjugated non-dominant side of the brain to feel free to express itself, resulting in an enlightened, fully-realized personality.

All of this, apparently, is pseudoscience.

I've suspected this for a while, frankly.  In my neurology class, we do a physical brain dominance test, and someone always asks about brain lateralization's role in personality.  When this happens, I have had to do something I am always reluctant to do, which is to say, "Well, I haven't seen any research, but this seems to me to be bogus."

I don't have to say that any more. 

Two weeks ago, the peer-reviewed journal PLOS-One published a paper by Jared A. Nielsen, Brandon A. Zielinski, Michael A. Ferguson, Janet E. Lainhart, and Jeffrey S. Anderson entitled, "An Evaluation of the Left-Brain vs. Right-Brain Hypothesis with Resting State Functional Connectivity Magnetic Resonance Imaging."  In this paper they describe a series of experiments that looked at the actual structure of the brain, and its connectivity -- and they found that there's no such thing as a "right-brain" personality and "left-brain" personality based upon anything real that is present in the brain wiring.  Here's what they said in their discussion section:

In popular reports, “left-brained” and “right-brained” have become terms associated with both personality traits and cognitive strategies, with a “left-brained” individual or cognitive style typically associated with a logical, methodical approach and “right-brained” with a more creative, fluid, and intuitive approach. Based on the brain regions we identified as hubs in the broader left-dominant and right-dominant connectivity networks, a more consistent schema might include left-dominant connections associated with language and perception of internal stimuli, and right-dominant connections associated with attention to external stimuli.

Yet our analyses suggest that an individual brain is not “left-brained” or “right-brained” as a global property, but that asymmetric lateralization is a property of individual nodes or local subnetworks, and that different aspects of the left-dominant network and right-dominant network may show relatively greater or lesser lateralization within an individual.

So the truth turns out to be more complicated, but more interesting, than the commonly-accepted model.  We tend to do that a lot, don't we?  After all, what is much of pseudoscience but an attempt to impress order upon nature, to make it fit in neat little packages, to make it work the way we'd like it to?  Astrology, for example, would have you believe that there are twelve personality types, and that anything about your behavior that needs explanation can be filed under the heading of, "Oh, but of course I'm like that.  I'm a Scorpio."

But the world is complex and messy, and doesn't care about our desire for order.  However, it is also beautiful and mysterious and fascinating, and ultimately, understandable.  And science remains our best lens for doing so, for blowing away the dust and cobwebs of our preconceived notions, and helping us to comprehend the world as it is.

And it works regardless of which side of the brain you're thinking with.