Brain lateralization of brain function refers to how cognitive processes (neural functions) are more dominant on one side of the brain than the other.This is part of the reason why people can be either left-handed or right-handed. The brain itself is composed of two hemispheres that are separated from each other by the medial longitudinal fissure. The two hemispheres of the brain are connected by a band of tissues called the corpus callosum that handles communication between the two brain hemispheres. Even though the two hemispheres appear to be identical to one another, each hemisphere contains unique neuronal networks.
Different types of skills, particularly language (left hemisphere) and spatial reasoning (right hemisphere) are controlled by different areas of the two hemispheres. It has been noted that when the corpus callosum is severed the two hemispheres will work independently of each other even to the point that if someone whispers into one ear the other side of the brain will have no knowledge of what was said.