The human brain is divided into several regions that, in combination, are responsible for the wide array of complex human functions. The three primary sections are the brain stem, the cerebellum, and the cerebrum, which is the largest, comprising almost 85 percent of the brain's total weight. Most scientists believe that the cerebrum is the area where all conscious mental activities occur.

Positive Phase Contrast


Negative Phase Contrast

The cerebrum is divided into two hemispheres by a deep groove termed the longitudinal cerebral fissure. Each side of the cerebrum is active in different functions. The right side of the cerebrum controls activities such as orientation, awareness, depth perception, and facial recognition. Creativity is also often associated with the right hemisphere. The left hemisphere is associated with logic, numbering skills, reasoning, and language.

The hemispheres consist of an inner core, referred to as white matter, and the cerebral cortex, the gray, wrinkled outer layer. The cerebral cortex is organized into six layers and is the location of most the activity in the cerebrum. The functional units of the cortex are vertical columns of neurons, or nerve cells, that run through the layers. Although specific functions are relegated to some of the layers, most of the neurons in the cerebral cortex are devoted to communicating with other neurons. Thus, the cerebral cortex is essentially a network of neurons necessary to coordinate various activities in brain.

The cortex is further divided into five lobes. The frontal lobe, the parietal lobe, the temporal lobe, and the occipital lobe are named for the skull bones that cover them. A fifth lobe, known as the insula, is internal and not visible from the outside. Each lobe is separated from the others by a fissure. Like the hemispheres, each lobe is associated with specific mental processes such as memory, recognition, and concentration.