Left Brain, Right Brain: An Outdated Argument

Kevin Boehm April 15, 2012 6

The right-handed bias has always been evident in humans, but scientists now are discovering that it is not uniquely human. Monkeys and other primates prefer to hold food with their right hands. Courtesy of 123rf.com.

“I am definitely a left-brained person — I am not very artistic.” How many times have we characterized ourselves as either left-brained and logical people or right-brained and creative people? This popular myth, which conjures up an image of one side of our brains crackling with activity while the other lies dormant, has its roots in outdated findings from the 1970s, and it seems to imply that humans strongly favor using one hemisphere over the other. More recent findings have shown that although there are indeed differences between the hemispheres, they may not be as clear-cut as we once thought.

Our personalities and abilities are not determined by favoring one hemisphere over the other — that much is certain. Many other functions, however, such as response to danger and language generation, are lateralized in the brain. Researchers hypothesize that these differences arose from early vertebrates. Originally, it seems that the right hemisphere began to respond more quickly to danger. In fact, when we are suddenly confronted by a dangerous stimulus, we will respond more quickly with our left hand, which is controlled by the right hemisphere. The left hemisphere, on the other hand, has developed to handle more common, routine tasks, such as feeding and hand control. Since this hemisphere controls the right hand, a strong right-handed preference has arisen in most of us, providing one explanation of why most people are right-hand dominant.

Language is another process that is lateralized in the brain, though a study conducted by researchers at Ghent University has shown that the asymmetry differs when generating versus receiving language. When children were shown images and asked to tell a story about them, function was lateralized strongly in the left hemisphere for over 90 percent of participating children. However, when asked to listen to an emotional story, both hemispheres of the brain were activated to a similar degree as planning and articulation require more processing involving more regions on both sides of the brain. The stories the children listened to, unlike the pictures, were emotional, which may indicate that the observed involvement of the right hemisphere is linked to emotional regulation.

The two hemispheres are separated except for the relatively narrow corpus callosum connecting them. This is the link between the processing centers and the source of many of our advanced abilities. Courtesy of Gray’s Anatomy, 1918.

Olivia Farr, a neuroscience Ph.D. candidate at the Yale School of Medicine, explains that this language lateralization is the source of many generalizations. “In some of the first studies conducted on hemispheric lateralization, split-brained patients without an intact corpus callosum, or bridge between the two hemispheres, were examined,” says Farr. Because visual information from the right eye goes to the left hemisphere, when split-brained patients saw a word with their right eye, they could speak it but not draw it. When the patients saw a word with the left eye, they could draw but not speak it. These results contributed to the belief that hemispheres operate independently of each other for most tasks, which then developed into the myth of being exclusively left-brained or right-brained. There was so little known about the brain that it was convenient to attribute poorly understood traits, such as personality or thinking habits, to a clear-cut difference in lateralization. However, “we now know that hemispheres are always communicating, and that even these lateralization rules don’t always apply,” Farr affirms.

Hemispheres sometimes do perform tasks nearly independently, but the integration of the two yields some of our most uniquely human characteristics. For example, when we make errors, our realization and ability to correct them is a result of the synergy of the two halves of our brain. In fact, patients with damage to the corpus callosum have difficulties correcting their errors as compared to patients with intact corpora callosa, further suggesting that the two halves of the brain are both involved in processing the error.

Even though some tasks usually occur preferentially in one half of the brain, it is possible for the part directly opposite to take control of the process. Such a process takes time, but after damage in the left inferior frontal gyrus (referred to as Broca’s area) — a region of the brain linked to speech production — researchers have found that activity in the right inferior frontal gyrus begins to increase during language generation. Our brains have enough plasticity to adapt to damage and change conformations, even as adults.

Knowing that language processing usually occurs on the left side of the brain and response to danger generally occurs on the right does not comprehensively summarize our beings. Lateralization of the brain is still not well understood, and there are very few, if any, hard and fast rules of lateralization that actually make an impact on our behavior. We are still every bit as human and unpredictable as before, but we now understand a bit more of what makes us that way.

6 Comments »

  1. Annonymous April 15, 2013 at 2:45 PM - Reply

    “Because visual information from the right eye goes to the left hemisphere, when split-brained patients saw a word with their right eye, they could speak it but not draw it. ”

    I do not believe this is the case, the left and right fields of both eyes are routed to the right and left hemispheres, respectively. Information seen with the left eye is routed to both hemispheres, the only exception being if the information is seen in the left or right field…then it will be routed to only one hemisphere. That is why stroke victims who suffered brain damage to the occipital lobe have missing field in both eyes. My father is missing large portions of the left field of both eyes due to a right hemisphere stroke.

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