What happens when patients undergo Split Brain Procedure?

By Bella Wang

The human brain is a very complex organ. Although it looks like a squishy walnut from the outside, it has an intricate system of nerves that make us, well, us. Due to technology like the Functional Magnetic Resonance Imaging (FMRI) and Position Emission Tomography (PET) scans, we now know that the brain is composed of many different parts such as the motor cortex, occipital lobe, and Broca’s Area that all control a part of us. The outermost, fleshy brain, otherwise known as the cerebral cortex, is composed of two hemispheres: the left and the right. The left side of the brain controls the right side of the body, while the right side controls the left. The corpus callosum is at the center of it all; a bridge made up of over 200 million nerve fibers that allow communication throughout the brain. Theoretically, humans can live with the two hemispheres working totally independently, but would life be different with a severed corpus callosum?

Due to how little we know about the brain, we often assume that any damage to the brain is bad. However, for some patients with severe epilepsy, splitting the corpus callosum in a surgery called split brain procedure is their best chance at living a “normal” life. Without treatment, they may experience seizures multiple times a day. These prolonged seizures may cause serious damage to the brain. The Split-Brain Procedure disconnects the two hemispheres, reducing the electrical storm to a single side of the brain which, in turn, reduces the severity and frequency of seizures. In some cases, the procedure has stopped the seizures altogether.

But are there any consequences to splitting the corpus callosum? An intriguing aspect about having two independent brains is how it shows how both hemispheres work. Normally, the left cerebral cortex is the analytical side of the brain and the control center for understanding human language and physical mechanisms of speech. The right side, on the other hand, controls things like visual awareness, facial recognition, spatial abilities, and more. Without communication between the two hemispheres, the individual functions of each become very apparent in a simple vision test. When split-brain patients are shown an image in only left eye’s peripheral vision, this visual information is only shown to the right hemisphere. The problem is that most people do not possess areas responsible for speech in the right hemisphere. When asked to name what they saw, the patient struggles to communicate, but when asked to draw the object, the right side of the brain does so perfectly.

In very rare cases, split brain patients have developed alien-hand syndrome after the procedure. in these cases due to the lack of communication and balance between the two hemispheres, the dominant side was taken over by the less dominant side (which was usually the right cerebral cortex). The alien hand syndrome’s most noticeable symptom was the abnormal, uncontrollable movement in the left hand. The right side of the brain, normally cooperative and docile, suddenly begins to rebel and create a ruckus, sometimes even doing the opposite of what the left side of the brain wants to happen. With the connection of the brain severed, so is the balance and cooperation between both hemispheres.

We know so little about the brain, yet so much. Our knowledge about the parts of the brain has become so advanced that we can preform procedures like splitting the brain without leaving patients drastically changed. Our technology today has allowed us to understand how we think, how we feel, and how we move.