Are we basically two people at once?
We like to think that each one of us is only one kind of person, a whole comprised of various facets and feelings. And as an extension of that, we like to think we have one brain — one brain that works as a unit to get everything done, and is completely in sync.
And usually, that is true — most people do have one brain that functions as an unbroken entity.
But sometimes they don’t. And that helps us learn more about ours.
The brain, as almost every eight-grader learns, consists of two halves: the left, and the right. Everyone — with extreme exceptions, of course — is born that way.
Everyone is also born with a series of nerve fibres that connect the two halves and pass information back and forth between them. These fibres are called commissures, and link similar areas of the brain. There are five such bundles — the anterior, the posterior, the hippocampal, the habenular and the corpus callosum.
In the early 1940s, William Van Wagenen performed the first split-brain surgery on two dozen epileptics for medical trials — he basically cut the commissures so that one hemisphere was inaccessible to the other.
Until that point, we didn’t know very much about what each specific half of the brain did. But then again, in the early 1940s, we didn’t know much about what any part of the brain did compared to what we now know, mostly because we couldn’t really look inside one belonging to a live person. (Imaging techniques such as CT and MRI were invented later, in the 60s and 70s.)
Van Wagenen’s split-brain surgeries or commissurotomies paved the way for us learn more about both the corpus callosum itself, and more importantly, how the two hemispheres worked in isolation from each other.
Ever heard anyone say that creative people are right-brained and logical people left-brained?
This is something scientists have been arguing about since at least the 70s, like the back and forth of papers between Michael Gazzaniga and Eran Zaidel about whether or not language is controlled only by the left hemisphere.
Gazzaniga did a series of studies to show this, but in order to understand the results better, there’s something you need to know. Contrary to what you might think, the left side of the brain actually receives pictures from your right eye and sensations from your right hand, and vice versa. This isn’t to say that there is no input from the right side of the body to the right brain, but that the information sent is more limited.
With eyes, it’s a bit more complicated. Eyes are so important, both eyes transmit pictures to both sides of the brain. But each side gets only half the picture — or half the ‘visual-field’, if you want to be technical. The right brain sees only the left half of your visual-field, and vice versa.
In the experiments, split-brain patients were shown the image of an object to the right side of their visual field. Generally, they were able to name it accurately. However, when the same image was shown to their left visual-field, they weren’t able to say what it was they had seen, but they were able to identify the object by feeling it with their left hand.
The right side of the brain, it seemed, did not have the ability to convert an image into language.
In another study, Gazzaniga flashed the word ‘smile’ on a screen to split-brain patients. When it was shown to their left brain, they usually smiled; when it was shown to their right, it elicited no reaction.
So, left brain — language brain? Not so fast.
Gazzaniga also did a study with a boy called P.S. (To preserve their anonymity, subjects in psychology case-studies are usually referred to by their initials).
P.S. had just had a commissurotomy — a split-brain surgery , where the connection between the two hemispheres of his brain was severed— but apart from that, he also had a damaged left hemisphere.
They would ask him part of a question verbally — like “what is your favourite”, and then flash the second part to either his left or right brain. When he was first tested, he was able to respond verbally only if it was flashed to his left brain, but had to use Scrabble tiles if it was to his right.
After a few years, however, he began to be able to orally identify objects and words flashed even to his right brain.
What was happening?
No one’s really sure, but neurologists think it might have been the right brain compensating for the left side’s inadequacies.
Okay, so what does the right hemisphere do?
Gazzaniga, along with fellow neurophysiologist Roger Sperry, filmed a subject named W.J. assembling building blocks based on a fixed preset pattern. W.J. had recently undergone split-brain surgery and was being studied with several others to try and understand the exact role of the right brain.
W.J.’s task was simple. He was given four cubes, each with two red sides, two white sides, and two sides that were split diagonally red and white. He was also given some cards with red and white shapes for him to replicate with the blocks, one hand at a time. He was watched by experimenter who sat next to him, taking notes, and at times, having to resort to taking one hand of W.J.’s off the table.
Here’s what they found: when W.J. used his left hand, he did fine. He completed the task quickly and didn’t make many mistakes. When he used his right hand, however, he did much worse. He fumbled, he knocked cubes over, and took a very long time to get it right. He made many mistakes along the way — including not realizing that he hadn’t used all four blocks in his pattern.
(If you watch the video, you’ll even see his left hand repeatedly come up to try and help his right, even when he knows it isn’t supposed to.)
Another example that illustrates this is an experiment conducted by Joseph LeDoux. He had patients draw a cube with both hands before and after having split-brain surgery. Before, most people’s right-hand cubes were better then their left-hand cubes — which makes sense, because they were usually right-handed.
But after the surgery, LeDoux found this flipped around. Peoples’ left-hand drawings were far better then their right-hand ones, even though their right hand was still dominant.
What he’d found was, the right brain was better at processing and visualising three-dimensional objects. Without the right-brain to help it, the left-brain, and the right-hand it controlled, failed miserably.
So, what does all that mean, anyway?
Basically, it means that the right brain is good at seeing things, as long as it doesn’t actually have to understand what it is that it’s looking at. The fancy term for it is ‘visuo-spatial tasks’.
So, left brain — language brain, right brain — sight brain? Not even this fast.
Neurologists now think these abilities for language and sight have less to do with the specific tasks themselves, and more to do with the higher processes involved in being good at them. We’ve found too much that tells us the language/sight division is too simplistic.
Some say that it has to do with the way the two hemispheres analyse information, but others think that we don’t have enough information to draw that kind of conclusion — they’re in two minds about it.
But, I think, after reading this, you’d find that much easier to understand.
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