Did you know that our brains have two halves, also known as hemispheres? Many people do not know this fascinating fact about their own brains! The overwhelming majority of people walking this planet have two distinct halves to their brains, but these two halves communicate with one another using a special brain structure. On rare occasions, however, these halves are completely disconnected from one other, resulting in what's commonly referred to as split brain. This term describes the condition resulting from disrupting communication between the right and left hemispheres of our brains surgically.
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Our two brain hemispheres are each divided into sections. Within each of these sections are areas or lobes controlling processes such as our vision, our movement, and our personalities. For example, the occipital lobe in the back of our brains is responsible for processing vision, and the frontal lobe behind our foreheads controls cognition and personality.
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The lobes of the brain are split between the right and left hemispheres of the brain. This anatomical arrangement means that for the lobes to function correctly, the two hemispheres of the brain must communicate with one another. How is this possible? Communication between the hemispheres occurs via a dense bundle of nerve fibers called the corpus callosum. The corpus callosum binds our two brain hemispheres together physically and communicatively. When this structure is damaged, like it would be if it were cut, the result is the aforementioned condition, split brain.
Scientific study on the split brain phenomenon really began during the early 1960s when doctors performed the first corpus callosotomy. This is a surgical procedure that severs part or all of the corpus callosum and can result in partial or complete disconnection between the two brain hemispheres. This initial surgery was performed to control grand mal seizures and was considered a great success. However, when the corpus callosum is severed, our two brain hemispheres can no longer communicate with one another as they do in a normal brain. This lack of communicative ability led scientists to investigate how tasks were divided within the brain hemispheres.
One such experiment attempted to determine how each hemisphere performed mathematical functions such as addition, subtraction, multiplication, and division. The results of this test indicated that the left hemisphere was significantly better than the right hemisphere at basic math functions. They made this statement based on the fact that the left hemisphere could correctly come to an answer approximately 90% of the time. The right hemisphere was closer to 50%.
Similar experimentation with split brain patients has uncovered other insights into the brain's functionality. For example, we now know that the right hemisphere excels at nonverbal and spatial tasks, while the left hemisphere has better verbal ability. We also know that the right hemisphere helps us recognize objects, and convey emotions such as empathy, humor, and depression. Conversely, our left hemisphere houses scientific and math skills. While we are beginning to understand more about the brain, the full extent of brain specialization remains the subject of intense scientific research and debate.
| Right Hemisphere | Left Hemisphere |
|---|---|
| Nonverbal and Spatial Tasks | Verbal Ability |
| Object Recognition | Scientific Ability |
| Emotion | Mathematical Ability |
Perhaps the most famous work in split brain research was completed by Sperry and Gazzaniga. These two scientists conducted a series of now famous tests on patients who'd had their corpus callosum severed. The tests shed light on the communicative nature of brain regions by uncovering the unusual cognitive abilities of split brain patients. The results of Sperry and Gazzaniga's early research indicated that in order to say you've seen or felt something, the part of your brain responsible for processing speech must be able to communicate with the part that processes visual or tactile stimuli. In other words, if you're holding a familiar object but haven't seen it, you may be incapable of verbalizing what it is.
Some of the most interesting research on split brain was completed with the assistance of a patient named Kim Peek. Kim was born with a split brain and never underwent a corpus callosotomy. Therefore, his two brain hemispheres developed independently of each other. As a result, Kim developed language areas in both brain hemispheres while growing up, and was rumored to have memorized over 9,000 books (an indication of his verbal acuity). However, Kim also had an IQ of 87 and couldn't button his own shirt. Kim's extremely enhanced and depressed cognitive abilities highlight both the brain's ability to learn as well as the need for hemispheres to be able to communicate during development. This type of understanding would not have been uncovered without split brain research and experimentation.
Split brain is the condition resulting from disrupting communication between our right and left brain hemispheres. Case studies grow by the day. Despite what we've learned, however, the field of split brain research and hemisphere specialization itself is still largely in its infancy. One way to continue study is to look at patients with a severed corpus callosum, the bundle of nerves linking our two brain hemispheres. The understanding of normal brain communication with a corpus callosum is generally understood, but brain functions and changes following a corpus callosotomy is still a mystery as it varies from patient to patient. However, research has taught us that the left brain hemisphere excels at verbal, scientific, and mathematical tasks, while the right brain hemisphere specializes in object recognition.
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