The paired occipital lobes of the brain play a major role in the visual processing of sensory data received from the eyes. Raw data is transformed into meaningful information, which is then transmitted to other areas of the brain. Located at the rear of the cerebrum beneath the occipital bone of the skull, this part of the brain is relatively well protected from injury. When injury does occur, loss of vision, visual distortions and hallucinations might occur. Studies analyzing injury or other damage in this portion of the brain have helped researchers determine the functions of the occipital lobe.
There are different areas within the occipital lobe for processing the movement of an object, its color, and its orientation in space. Although each of these aspects is processed individually, the information is again processed to form a single, meaningful image. Damage to specific areas of the lobe can result in spatial distortions, with objects appearing too large or too small. Colors may be absent or altered when a different area of the lobe is impaired. If the primary visual processing area suffers damage, a total loss of vision might occur.
Studies of patients with conditions affecting the this area show that hallucinations and illusions appear to be generated by this visual processing area of the brain. Damage to this are of the brain can be caused by tumors, injuries and strokes. A rare form of epilepsy — occipital epilepsy — is accompanied by visual symptoms. Fleeting visualizations of flashes of light and color, loss of vision, or spreading hallucinatory patterns are characteristic of occipital epilepsy episodes. These are similar to migraine auras, but are usually more colorful and appear for only seconds.
Tumors and lesions in this area cause visual disturbances and disruptions. Vision may be lost in one or both eyes. It may be blurry, or images may be doubled. The ability to recognize familiar objects and faces may also be impaired. All of the visual symptoms caused by any form of damage to this part of the brain help researchers pinpoint the roles played by specific areas of the occipital lobe.
In addition to its visual processing duties, the occipital lobe of the brain is believed to play a role in dreaming. One study investigated the reported loss of dreams in a stroke patient whose occipital lobes were damaged. Although she also suffered a loss of vision for a few days, the complete loss of dreams continued for months. She had no other sleep disturbances, still experiencing rapid eye movement (REM) sleep, but no accompanying dreams. One year after the stroke, the patient was dreaming again, but not with the frequency or vividness she experienced before the stroke.