What Happens When You Cut a Brain in Half?

Came across Michael Gazzaniga’s work on brain research. He and his colleagues worked with epilepsy patients to study the effects of a “split brain.” (Some epilepsy patients undergo surgery that severs the corpus callosum, which is the bundle of neurons that connects the left brain with the right). The results of the experiments are fascinating:

It became clear that visual information no longer moved between the two sides. If we projected an image to the right visual field—that is, to the left hemisphere, which is where information from the right field is processed—the patients could describe what they saw. But when the same image was displayed to the left visual field, the patients drew a blank: they said they didn’t see anything. Yet if we asked them to point to an object similar to the one being projected, they could do so with ease. The right brain saw the image and could mobilize a nonverbal response. It simply couldn’t talk about what it saw…

[In another case a] left-handed patient spoke out of her left brain after split-brain surgery —not a surprising finding in itself. But the patient could write only out of her right, nonspeaking hemisphere. This dissociation confirms the idea that the capacity to write need not be associated with the capacity for phonological representation. Put differently, writing appears to be an independent system, an invention of the human species. It can stand alone and does not need to be part of our inherited spoken language system.

And on false memories:

My colleagues and I studied this phenomenon by testing the narrative ability of the left hemisphere. Each hemisphere was shown four small pictures, one of which related to a larger picture also presented to that hemisphere. The patient had to choose the most appropriate small picture.

…[T]he right hemisphere —that is, the left hand—correctly picked the shovel for the snowstorm; the right hand, controlled by the left hemisphere, correctly picked the chicken to go with the bird’s foot. Then we asked the patient why the left hand—or right hemisphere—was pointing to the shovel. Because only the left hemisphere retains the ability to talk, it answered. But because it could not know why the right hemisphere was doing what it was doing, it made up a story about what it could see – namely, the chicken. It said the right hemisphere chose the shovel to clean out a chicken shed.

Read the whole article.


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