Left-brained, right-brained, or all-brained?

Last update: March 1, 2024
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Reading time: 3 minutes
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By Brain Matters

When it comes to talking about the potential of our brains, fiction writers of the last century have been pretty obsessed with the idea that we are only using a fraction of our untapped potential. From Robert Louis Stevenson’s Dr Jekyll and Mr Hyde to the 2014 film ‘Lucy’ that spawned a whole series of jokes about only using 10% of our brain in our daily lives - a great deal of fiction has explored the “boundaries” of the mind. Science fiction is, as the name emphasises, fiction. Yet, the notion that some of our brain potential is untapped persists in writing beyond the realm of fantasy. A common example of this is Betty Edwards’ book “Drawing on the right side of the brain”, where she explains her success in art being due to her ability to tap into the creative right side of the brain in a world that is mostly left-sided. This begs the question, where did the notion of left and right-sidedness come from and how much truth is there to the myth?

At the start of the 20th century, the two neurologists Broca and Wernicke determined through studies of patients with damaged brains that areas of the left hemisphere were responsible for the processing and production of language. This inspired the understanding that areas of the brain are specialised, where specific regions or even sides could be responsible for certain functions and behaviours. At the time, such ideas were the inspiration for the characters Jekyll and Hyde, the former representing the articulate, rational left hemisphere, and the latter the more emotional and irrational right hemisphere. However, it wasn’t until the 1960s that the terms left and right-brained really entered the public vocabulary.

Epilepsy is a disorder that can often result in seizures due to abnormal neural activity across areas of the brain and is often highly disruptive to those who suffer from the condition. While there have been numerous drug discoveries over the years that have shown great potential in relieving symptoms for many, there persist a few cases where patients are completely drug resistant. In these severe cases, doctors would (although very very rarely) conduct a surgery known as “corpus callosotomy”, or the severing of the corpus callosum (the main bundle of nerves that connects the two hemispheres). It was studies on these patients with severed corpora callosa that spawned the now ingrained myth of the left and right-sided brains.

During the 1960s neurologists Roger Sperry and Michael Gazzaniga conducted a split vision study on four split-brained patients. The patients were asked to look at a fixation point on a screen, after which an image was flashed that corresponded to either the left or right visual field. When the participant saw an image, they were supposed to report what they saw and push a button next to their hands. The results intrigued the neurologists enough to pursue further split-brained patients to study. When the patient perceived an image in their right visual field (which is processed in the left brain), they announced what they had seen and pushed the button; but, when the image was flashed in their left visual field (which is processed by the right brain), they did not declare having seen anything, yet pushed the button with their left hand seemingly independently. This led Gazzaniga and Sperry to conclude that the left hemisphere is the site of verbal processing. Meanwhile, in the case of the split brain patients, the right hemisphere could not communicate with its counterpart. To top it all off, the patient was able to draw the stimulus they saw in their left visual field even when they could not report on it vocally. 

Research continued to emerge slowly over the next two decades showing how split-brain patients could only communicate verbally with the left side of the brain, while the right side could interpret with the left hand by drawing its responses, seemingly of its own volition. Naturally, news of these studies led the world to adopt its own interpretation. The right hemisphere was clearly the more different, quieter and visually artistic, when compared to the “normal”, well-spoken left hemisphere. Once more, left-handedness became a trait that must have behavioural correlates, after all it had a direct connection to that artistic right hemisphere. As the terms left-brained and right-brained began to arise in popular culture, so too did it begin to reflect back on the field of neuroscience, leading to greater and greater numbers of researchers believing these myths despite the lack of clinical evidence.

This article lays the groundwork for how the myth arose in popular science and wider fiction. In part 2, Jennifer Morael will look into the ongoing research on the left-right division and separate fact from fiction.

Author: Thomas von Rein

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