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Health and Disease

Split-Brain: Unbridging the bridge

By Shreyas Gupta

Published 11:17 EST, Thurs December 23rd, 2021

Introduction

Many instruments and sports involve considerable hand-eye coordination and require thousands of hours to master. Whether this is playing gentle chords on an acoustic guitar or the powerful smash of a tennis ball, these instruments and sports involve a specific region of the brain called the Corpus Callosum, and without this important brain region daily life tasks would become impossible. 

Corpus callosum (Critical bridge)

The Corpus Callosum is the biggest cluster of white matter cells in the brain, consisting of 200–300 million myelinated nerve fibers, which provide connections in the brain. 

The corpus callosum has four regions: the rostrum, genu, body, and splenium. The rostrum and genus connect the left and right frontal lobes of the brain, and the body and splenium connect the temporal lobes and the occipital lobes.

The main role of the corpus callosum is to transmit information from both cerebral hemispheres that help in vision, audition, communication, and cognition.

Robert Sperry

Psychobiologist Roger Sperry’s vast work studying the corpus callosum revolutionized the way we perceive the human brain. Sperry found that when the corpus callosum was severed from connecting both hemispheres, the brains would function independently of one another. Astounded by this new discovery, Sperry titled this phenomenon accordingly as “split-brain”. While studying the split-brain, he found that test subjects exhibited enhanced memorization capabilities. Intrigued, Sperry further researched and decided to test other applications of the “split-brain procedure,” hoping he would find some medical uses for his discovery. Confident in his work, Sperry eventually tried his split-brain procedure on human patients, severing the corpus callosum on many humans who had epilepsy or other types of seizure disorder, deducing that the procedure was a viable treatment. In addition, many patients with severed corpus callosum did not show any major difference in how they function from those with no severed corpus callosum. However, this did not help him answer the major underlying question: why isn’t there a major difference in how both sets of patients act and talk? Shouldn’t there be huge consequences for splitting the brain structure in half? Sperry took back to the drawing board and designed a new experiment involving cats and monkeys with severed corpus callosum. Sperry knew that the hemispheres of the brain were responsible for the functions of the respective side of the body. For example, the right hemisphere controls your right eye, arm, and leg. With this experiment, Sperry concluded that he would carefully monitor what the eyes of the cats and monkeys saw. The experiment involved the use of an eyepatch and 2 blocks, block a and block b, and the eyepatch was used to cover one eye of the cat. Sperry would then place food under block A and have the cat memorize under which block the food was stored. Sperry then repeated this experiment on the other eye, but this time had the cat memorize that the food was under block b. When the eyepatch was taken off completely the cat was not able to distinguish between blocks. With this new information, Sperry deduced that both events must have been memorized separately from each other. Leading to the conclusion that once the corpus callosum had been severed, both hemispheres acted separately from each other, functioning as the only brain. His similar experiment with monkeys and humans proved his conclusion further.

Robert Sperry’s work in split-brain procedures helped contribute to the later proven research in the field of brain lateralization, a field of research focusing on how different parts of the brain have different functions and responsibilities.

Split-Brain Procedure

Split – Brain Syndrome, also known as callosal disconnection syndrome is characterized by the neurological abnormalities that come with partial or full lesion of the corpus callosum severing both brain hemispheres from each other. A major cause of Split-brain syndrome is the surgical procedure called a callosotomy. While this procedure is rarely ever performed nowadays it is often used as a “last-resort” for patients with severe epilepsy or any other seizure disorder. Other less common causes of split-brain procedures are tumors and ruptured arteries causing the bundle of nerve fibers connecting the 2 hemispheres to be severed. Many patients with split-brain syndrome retain their memory and social skills. They also retain any motor skills that were known prior to the split-brain procedure, including walking, running, swimming, and biking. The patients can also perform coordinated movements such as clapping, jumping, and stretching. However, patients cannot perform any motor skills that require the interdependent movement of body parts, such as playing instruments. The eyes cannot move interdependent of one another, as both must move in synchrony. Other augmentations include the patient’s ability to recognize objects with blindfolds over one eye. As the brain hemispheres can no longer communicate with one another, this becomes an impossible endeavor.

Shreyas Gupta, Youth Medical Journal 2021

Works Cited

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