What happens when the corpus callosum is severed?
What happens when the corpus callosum is severed?
The corpus callosum is a thick band of nerve fibers (white matter) connecting the left and right cerebral hemispheres. When this structure is severed—a surgical procedure known as a callosotomy, typically performed to treat severe, drug-resistant epilepsy—the primary communication bridge between the two halves of the brain is destroyed.
The "Split-Brain" Effect
Because the human brain is contralateral (meaning the left hemisphere controls the right side of the body and processes sensory input from the right visual field, and vice versa), severing the corpus callosum creates unique cognitive phenomena often studied by neuroscientists:
- Visual Isolation: If an image is presented solely to the left visual field (processed by the right hemisphere), a split-brain patient may not be able to verbally name the object, because the speech center is typically located in the left hemisphere. However, the patient's left hand (controlled by the right hemisphere) may be able to successfully draw or pick up the object.
- Independent Processing: The two hemispheres can process different information simultaneously, occasionally leading to conflicting behaviors, such as one hand buttoning a shirt while the other hand unbuttons it.
Medical Outcomes
Despite these fascinating behavioral quirks, patients who undergo a callosotomy generally retain their overall personality, intellect, and general motor coordination. Most importantly, the procedure is remarkably effective at stopping or reducing the severity of epileptic seizures by preventing electrical storm activity from spreading from one hemisphere to the other.