The Cerebrum

Most high-level processes, such as reasoning, take place in the cerebrum, which makes up about 85% of the human brain's weight. The outer surface of the cerebrum is the convoluted (folded or wrinkled) cerebral cortex made out of a layer of cells called gray matter. The convolutions are made of bulges called gyri, as well as small grooves (sulci) and large grooves (fissures). Around two-thirds of the cortex is hidden in the sulci, allowing a relatively large surface area of 1.5 m2 (16 ft2) to fit inside the cranium. Underneath the gray matter lies a collection of nerve cell fibers called the white matter. These fibers connect parts of cortex, or they connect the cortex to the cerebellum, brain stem, and spinal cord. The largest of these is the corpus callosum.

As you can see in the diagram, the cerebrum consists of two hemispheres that are separated by the longitudinal fissure. The two parts of the cerebrum interact by means of a bundles of axoms called commissures. A person's dominant hemisphere usually controls language and logic. The other hemisphere controls emotions and artistic skills. In most right-handed people and even in some left-handed people, the left hemisphere is dominant.

The cortex is divided into five different regions by large sulci such as the central sulcus (Rolandic Fissure) and the lateral (Sylvian) sulcus. The regions are called the frontal lobe, parietal lobe, temporal lobe, occipital lobe, and insula. Other areas within the cortex that have specific functions have been mapped. These include the motor and sensory cortex, as well as the associative cortex which processes information and carries out complex responses.