What would involve in a surgery for an epileptic?

Cutting the corpus callosum. This is only in extreme cases because it causes other (less severe if it serious epilepsy) problems, and it is done because the corpus callosum attaches the two hemispheres of the brain so they can communicate with each other. In an epileptic seizure, electrical activity moves throughout the brain in a random order, and the cutting of the corpus callosum prevents this signal from travelling from one side to the other.