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Split-Brain Patients

Updated: Feb 13

By Samira Mehta


Image by Huixuan Liang for Knowing Neurons

The brain is often called the “black box” because most of its inner workings are wonders that are yet to be discovered by scientists. It has revealed that certain parts of the brain carry out specialized functions. For example, the occipital lobe (towards the back of your head) is the main center that processes visual information, and the temporal lobe (located on the left and right sides of your head) is where auditory information is processed.


It has long been known that the brain is composed of a right half and a left half that are connected by the corpus callosum, a communication highway between the two parts of the brain. Most functions are symmetric, meaning that there are visual centers, for example, on both sides of the brain. Why is that? This is because the body is “handed,” meaning that what occurs on the right side of the body is processed by the left hemisphere of the brain. For example, if you touch something warm with your right hand, the information is carried to the left side of the brain for processing. The right side of the brain learns of this information when it travels through the corpus callosum to right side.


In the 1950’s, however, research on patients with brain injuries suggested that speech and language centers are primarily located on the left side of the brain. This means that if you touch something warm with your right hand, it will travel to your left brain and you will be able to say “this is warm.” However, if you touch something warm with your left hand, the information travels to the right side of the brain for processing and must travel through the corpus callosum to the left side of the brain before you can say “this is warm.”


So, what happens when the corpus callosum is cut? This question was answered in 1962 when a man known as Patient W.J. was the first person to have his corpus callosum cut. Prior to having this procedure, the patient suffered from severe seizures, or sudden electrical disturbances in the brain that can cause irreparable damage. In order to prevent the seizures from happening on both sides of the brain, Patient W.J.’s corpus callosum was cut so that his two brain hemispheres no longer communicated with each other. The operation was successful and significantly reduced the frequency of his seizures and the damage done by them. Surprisingly, shutting down the communication highway between the two hemispheres of the brain had little impact on the patient’s higher functions. He could perform tasks, like going to work and driving his car, without issues.


Michael Gazzaniga and Roger Sperry were the first to do research on split-brain patients like W.J., giving us insight into the importance of the communication between the two parts of the brain, specifically relating to language and speech. In a famous experiment, a split brain patient sat in front of a screen. A word, such as “face,” was flashed on the right side of the screen. The right eye saw this word and the information was processed by the left side of the brain where the speech centers are located. The patient was then asked what he saw, and he said that he saw the word “face.” Then, the patient was asked to look at the screen again. This time, the word “face” was flashed on the left side of the screen. When the patient was asked what he saw, he said he didn’t see anything. However, when he was asked to draw with his left hand what he saw, even though he wasn’t consciously aware that he had seen the word “face,” his left hand drew a face. Why is that? When the word flashed on the left side of the screen, it was processed in the right side of the brain, but the information was not able to travel through the corpus callosum to the left side of the brain where the speech centers are located. For this reason, the patient was not able to say that he had seen anything. Even though he was not able to say what he had seen, the right side of the brain had in fact processed the information. For this reason, when asked to draw the word he had seen with his left hand, the patient was able to draw a face. Fascinating! While research like Gazzaniga’s has given us great insight into one of the many mysteries of the brain, it remains a black box of exciting wonders that are yet to be understood.


Image from tutor2u

Sources:

1. Gazzaniga, Michael S. Psychological Science. New York: W.W. Norton & Co, 2018. Print.

Editor: Jo Ann Sun

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