context: The corpus callosum is a band of nerve fibers located deep in the brain that connects the two halves (hemispheres) of the brain. It helps the hemispheres share information, but it also contributes to the spread of seizure impulses from one side of the brain to the other. A corpus callosotomy is an operation that severs (cuts) the corpus callosum, interrupting the spread of seizures from hemisphere to hemisphere. Seizures generally do not completely stop after this procedure (they continue on the side of the brain in which they originate). However, the seizures usually become less severe, as they cannot spread to the opposite side of the brain. A corpus callosotomy, sometimes called split-brain surgery, may be performed in people with the most extreme and uncontrollable forms of epilepsy, when frequent seizures affect both sides of the brain. People considered for corpus callosotomy are typically those who do not respond to treatment with antiseizure medications. Candidates for corpus callosotomy undergo an extensive pre-surgery evaluation -- including seizure monitoring, electroencephalography ( EEG), magnetic resonance imaging ( MRI), and positron emission tomography ( PET). These tests help the doctor pinpoint where the seizures begin and how they spread in the brain. It also helps the doctor determine if a corpus callosotomy is an appropriate treatment. A corpus callosotomy requires exposing the brain using a procedure called a craniotomy. After the patient is put to sleep with anesthesia, the surgeon makes an incision in the scalp, removes a piece of bone and pulls back a section of the dura, the tough membrane that covers the brain. This creates a "window" in which the surgeon inserts special instruments for disconnecting the corpus callosum. The surgeon gently separates the hemispheres to access the corpus callosum. Surgical microscopes are used to give the surgeon a magnified view of brain structures. In some cases, a corpus callosotomy is done in two stages. In the first operation, the front two-thirds of the structure is cut, but the back section is preserved. This allows the hemispheres to continue sharing visual information. If this does not control the serious seizures, the remainder of the corpus callosum can be cut in a second operation. After the corpus callosum is cut, the dura and bone are fixed back into place, and the scalp is closed using stitches or staples. The patient generally stays in the hospital for two to four days. Most people having a corpus callosotomy will be able to return to their normal activities, including work or school, in six to eight weeks after surgery. The hair over the incision will grow back and hide the surgical scar. The person will continue taking antiseizure drugs. Corpus callosotomy is successful in stopping drop attacks, or atonic seizures in which a person suddenly loses muscle tone and falls to the ground, in about 50% to 75% of cases. This can decrease the risk of injury and improve the person's quality of life. The following symptoms may occur after having a corpus callosotomy, although they generally go away on their own: Scalp numbness Nausea Feeling tired or depressed Headaches Difficulty speaking, remembering things, or finding words Paralysis, weakness, loss of sensation Change in personality Serious problems are uncommon with a corpus callosotomy, but there are risks, including: Risks associated with surgery, including infection, bleeding, and an allergic reaction to anesthesia Swelling in the brain Lack of awareness of one side of the body Loss of coordination Problems with speech, such as stuttering Increase in partial seizures (occurring on one side of the brain) Stroke