The brain can be divided into three major portions -- the cerebrum, cerebellum, and brain stem, with the cerebrum making up about 83 percent of the brain's volume divided into two cerebral hemispheres. Gyri, thick folds or "mountains," are separated in the brain's topography by "valleys" or shallow grooves called sulci. The cerebral cortex (outer layer of gray matter) functions to allow us to perceive, communicate, remember, understand, appreciate and initiate voluntary movements -- all of which compose conscious behavior. The parietal lobe of the cerebral cortex is largely concerned with the integration of sensory information with the exception of hearing, smell and vision (which occur elsewhere in the brain).