The cerebral hemispheres are literally the two halves of the brain. They are identified on the outside or external surface by the folded hills (gyri) and valleys (sulci). The deep longitudinal fissure runs down the sagital (middle) plane of the brain and separates the two halves of the cerebrum. It clearly shows the separation between the two hemispheres. The hemispheres make up about 83% of the volume of the human brain. They are connected to one another by a thick bundle of nerve fibers, the corpus callosum.

Different lobes have been identified in the hemispheres that are named for the cranial bones that overlie them. The neuroanatomy of the hemispheres is simple in that the majority of the tissues are myelinated white matter covered by a thin layer of gray matter, the neocortex. However, the function of the regions of the hemispheres is complicated. Regions of the...