Split Brain: Definition, Research & Experiments

Instructor: Dominic Corsini
Our brains contain two hemispheres. What happens if you disconnect those hemispheres from one another? This lesson addresses that question through an investigation into the concept of a split brain.

What is a Split Brain?

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.

Right and left hemispheres of the brain
Cerebral hemispheres

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.

Some major lobes of the brain
Brain lobes

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.

Research and Experiments

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.

Hemisphere Specialization

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.

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