Which structure, if transected, will prevent the cerebral hemispheres from communicating with each other?

The corpus callosum is what connects the left and right cerebral hemispheres of the brain. If it is severed, it would no longer be able to allow the two sides to communicate. In some cases, it is partially transected (severed) in patients that have severe epilepsy. The procedure is called a corpus callosotomy and is only done as a last resort.