Split-Brain Syndrome

The procedure called the corpus callosotomy involves the severing of the left and right hemispheres of the brain. Due to the disconnection of the right hemisphere from the left, the patient will suffer from what is known as split-brain syndrome. This makes the patient incapable of learning any new tasks that involve the independent coordination of both sides of their body. This is because those kinds of tasks would require the left and right hemispheres to communicate and coordinate with one another to create movement. The patient will still be able to perform tasks that they have previously learned and have muscle memory for, like walking, but things such as learning to play the piano are no longer possible. Exceptions to this limitation also include movements the involve one hand copying or mirroring the other (Sand).

Another symptom of split-brain syndrome is limitations with verbal communication. The left hemisphere is the only hemisphere with the ability to produce language (Sand). This means that if information about what the patient is seeing or physically touching cannot reach the left brain, they will not be able to say what it is they are seeing or touching. For example, if a patient has their right eye covered and they are shown the picture of a square, they will not be able to say what they saw. This is because their left eye saw the picture and transferred that info to the right hemisphere of the brain by way of the optic nerve. In order to convert what they saw to speech, the information must be relayed to the left hemisphere’s language cortex. But since the corpus callosum is split, the information is stuck in the right brain. However, then if the patient is asked to draw what they saw with their left hand, they will be able to draw a square. That is because the right brain was still able to send the information to the left hand, so the patient would be able to draw it.

This phenomenon can be seen in a video of split-brain patient “Joe” as a few experiments are performed on him. Joe underwent the corpus callosotomy surgery in order to treat his severe epilepsy. Now with his corpus callosum severed, he is a split-brain patient. Joe was told to stare at a dot in the center of a screen while a picture of grapes was flashed to the right of the dot. That visual stimulus was picked up by his right eye and was then relayed to his left brain. The language center in the left brain then allowed him to speak the word “grapes” when he was asked what he saw. Then the word “PAN” was flashed on the left side of the screen, feeding the stimulus to his left eye and therefore the right brain. When asked what he saw, Joe said he didn’t know. But then when he was asked to close his eyes and let his left hand draw what he saw, he drew a clear picture of a pan. His right brain was unable to produce the speech, but it was still able to direct his left hand to draw the picture. Even stranger, Joe was flashed two pictures at the same time: there was a saw on the left side of the screen and a hammer on the right side of the screen. When asked what he saw, Joe responded “hammer” since that was what his left brain picked up. But when he was asked to close his eyes and let his left brain draw what he saw, he drew a picture of a saw (Markmcdermott).

I will be continuing to learn more about experiments done on split-brain patients like Joe, and in my future posts I will discuss more about how the corpus callosotomy procedure works and the differences between partial and complete agenesis of the corpus callosum.


Sand, Rheanna. “Split-Brain Syndrome.” Encyclopædia Britannica , Encyclopædia Britannica, Inc. , 19 May 2016, www.britannica.com/science/split-brain-syndrome.

Markmcdermott, director. Split-Brain Patient ‘Joe’ Being Tested with Stimuli Presented in Different Visual Fields . YouTube, 5 May 2010, www.youtube.com/watch?v=aCv4K5aStdU.


  1. clopezsilva says:

    I have always found Split-Brain Syndrome quite phenomenal; in a patient like Joe, it’s clear from the beginning he understands the disconnection that exists between his two hemispheres and yet, he struggles to perform simple tasks that require their cooperation. Some might say the results of this study are somewhat counterintuitive: how can he easily draw a pan and yet be unable to vocalize the word? But this is what makes neuroscience such an exciting field. We tend to think of the human brain as a single unit that is responsible for making sense of reality, but what we can learn from patients like Joe is that our perception and interactions with the world are the result of an intricate process of coordination between independent regions of the brain; when this connection is interrupted by the severing of the corpus callosum, problems such as Split-Brain Syndrome arise.

    I really look forward to reading your next entries as your project develops and learning more not only about Split-Brain Syndrome but also about other conditions of the corpus callosum. For example, I wonder how the processes such as language acquisition and motor development of an infant suffering from agenesis of the corpus callosum (or as you mentioned, partial agenesis) might differ from those of a healthy one. It would be a really interesting read!

  2. First of all, I think your cousin’s story is amazing, extraordinary, and gives hope to others suffering like he had. These kinds of stories are what make me want to study the brain and how concussions and other traumatic events affect our functionality, like how you asked how the corpus callosotomy affects the functionality of those patients. It’s fascinating and confusing to us who have a fully intact brain, how people like Joe after the surgery can only name the object if they see it with their right eye and can only draw it if they see it with their left eye. These patients allow us to observe the effects and roles of the two hemispheres of the brain and what each one is able to do depending on where the individual received the stimulus, they also highlight the intricate circuits and wiring in the brain that we take for granted every day. This somewhat relates to those with second impact syndrome, which is when one person gets a concussion on top of another one, in that their corpus callosum is greatly deteriorated and have difficulties in similar aspects that split-brain patients have, but obviously to a lesser extent since they still have a connection albeit a weaker one. I think that you have chosen a great topic that I and I’m sure many others find interesting and want to find out more. I look forward to following your research throughout the summer!