In a series of experiments patient’s brains were cut in half—while they were still alive. The earliest records of these experiments took place in the 1940s in Rochester, New York. This procedure, though it sounds gruesome, was actually used as a treatment to manage seizures.
The Burden of Seizures
Seizures are often described as “electrical storms” that result from brain cells misfiring electrical signals. Some people who experience seizures can sense them coming when they have a fever, are experiencing drug or alcohol withdrawal, or have low blood sugar. Others are caught by surprise when their seizures occur unprovoked. These spontaneous seizures occur in many patients with a condition known as epilepsy, which affects about 1% of the population.
But why would any of these patients agree to such an invasive procedure? Seizures can be so severe that they reduce a person’s quality of life or cause injury. During tonic clonic seizures (previously known as “grand mal” seizures) patients can lose consciousness and lose control of their bodies. As they lose muscle control and begin to twitch and jerk uncontrollably, they can fall to the floor and harm themselves. These seizures can last for several minutes and in severe cases can occur several times a day, leaving patients weak, sore, and exhausted. This post-seizure exhaustion can last for an entire week and prevent patients from completing normal activities or being able to work.
For patients who do not respond to anti-seizure medications and conventional treatments, the split brain procedure was their last resort.
Splitting the Brain
In the split-brain experiments scientists surgically severed the corpus callosum, a section of the brain that contains 200 million nerve fibers and connects the left and right hemispheres of the brain. By severing the corpus callosum, scientists were essentially destroying the communication between the two hemispheres. This treatment would effectively limit the electrical storm to just one side of the brain, reducing both the length of the seizure and the risk of injury from it.
This procedure, known as a corpus callosotomy, is usually performed one of two ways. First, the connections between the two hemispheres are maintained, and the other, where the hemispheres are completely separated. Most surgeons will start with the more conservative option, and if seizures persist, then they will have a second surgery to complete the separation. According to the Children’s Hospital of Philadelphia, the surgery reduces the frequency of generalized seizures by 70-90% in most patients.
The Ominous Side Effects
Despite the success of the procedure, some patients reported feelings of confusion and frustration in their daily lives when the two sides of their brains seem to be “fighting” with each other after the split. For example, one patient described the simple task of grocery shopping as infuriating. While in the store, she would consciously think of one item she wanted, but her hand would reach for a separate item without her even knowing. She described the feeling of having a split brain as “almost like repelling magnets.” This experience was not an isolated incident, and was reported by several patients after recovery.
A Tale of Two Brains
To understand why this is happening, we have to understand that each half of your brain controls the opposite half of your body. The left hemisphere controls the right side, and the right hemisphere controls the left side. It is also important to note that the left brain is responsible for speech and language while the right brain is considered “mute.”
After severing the corpus callosum, the left and right hemispheres of the brain are no longer able to communicate with each other. That’s why when patients were asked a question, they responded both verbally and physically, but with different answers. For example, when asked their favorite color a patient could say their favorite color was blue, but their hand would reach out to grab a green object.
This phenomenon was so peculiar that scientists designed a simple experiment to study it. Patients were shown an image to only one eye at a time. Their rationale was that the left eye would bring visual input to the right side of the brain, and the right side would provide input to the left side. This way, researchers could ask a specific question to each side of the brain.
Through these experiments scientists learned that the right brain, which is “mute”, couldn’t respond but could draw its answers. So, when the right brain was presented with an image and was asked to describe what they saw, patients would often respond with “I don’t know.” Surprisingly, they were able to draw the image on paper. In a similar way, when the right brain was presented with a word, patients were unable to remember what that word was—supporting the idea that the right brain is incapable of understanding language. That is the job of the left brain.
These studies taught scientists that when the two hemispheres of the brain were split, they were functioning independently of one another, which may explain the reason why patients who were asked one question had two different answers. The two brains were simply not communicating with each other.
Despite the frustrating experience, there are some advantages to having a split brain (besides being cured from severe seizures). Animal experiments show that individuals with split brains can memorize twice the amount of information at one time. Dr. Roger Sperry, the scientist behind a majority of this split-brain research, received the Nobel Prize in Physiology or Medicine in 1981 for this work which established our understanding of lateralization of function, or how specific regions of the brain control specific functions.
Who’s in Charge?
The split brain studies have raised many questions about our modern understanding of the brain and of consciousness. One major question asked is, which side of the brain are you? Are you the verbal mind or the nonverbal mind? Does a split brain lead to split consciousness? Is the nonverbal mind trapped, only to be heard after the split? These questions have remained unanswered and have been highly debated.
An Uncertain Future
Unfortunately, the window for split brain research is closing. Thanks to new non-invasive therapies for epilepsy there are only a few people in the world who have split brains, and fewer brains left arguing amongst themselves.
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