The occipital lobe is the primary visual processing center of the mammalian brain. It is one of the four main lobes of the brain and is located in the posterior region of the cerebral cortex. There are two occipital lobes, one each on the right and the left hemispheres of the brain. The occipital lobe is involved in visual perception and color recognition. This particular lobe is not very vulnerable to injury because of its location at the back of the brain. However, any significant trauma to the brain could cause subtle changes to the visual-perceptual system. Damage to the occipital lobe can cause blindness or a condition called cortical blindness. People with this condition have no pattern of perception and no awareness of visual information.
Anatomy and Function
The primary visual cortex (PVC) is the main region of the brain that is responsible for sight and is called Brodmann area 17. This area of the brain recognizes size, shape, color, light, motion, and dimension of objects. For example, the PVC helps a person identify the basic features of a pencil—the edges, the amount of light, and its location in space. The PVC sends signals to other cortical regions called the visual association areas, which are located in the posterior portions of the temporal and parietal lobes. It is the visual association areas that interpret the information received from the PVC and helps a person recognize an object as well as recall its name, such as goldfish, book, face, or television.
The visual cortex is made up of several neurons that will respond to a specific stimulus like light, color, or movement. The region within the occipital lobe in which a neuron will be activated is called a receptive field. The neurons contained in the receptive fields are named based on the stimulus that is needed to activate them. For example, simple cells may respond only to light. Complex cells may respond to light moving only from left to right, while hypercomplex cells may respond to a two-inch length of light moving from left to right. These receptive fields help to determine the physical features of objects that a person sees.
In addition to receptive fields, the PVC contains columns of cortical neurons that respond from input of either the left or right eye. These are called ocular dominance columns. It has been hypothesized that these columns are required for binocular vision as a person who has input from a single eye will not have well-formed columns. Other studies, however, suggest that ocular dominance columns may result from visual development and may not have a true function.
Damage to the Occipital Lobe
In rare cases, the occipital lobe may be injured from accidents such as vehicle crashes or falls. Damage to the occipital lobe can cause blindness or a condition called cortical blindness. People with this condition have no pattern of perception and no awareness of visual information. Injuries to the parietal-temporal-occipital visual association areas may cause visual defects like having (1) problems locating objects, (2) difficulty with color recognition (color agnosia), or (3) trouble with reading (alexia) and writing (agraphia).
Another common problem in the occipital lobe is occipital seizures. These seizures are often mistaken for a migraine headache due to the similar symptoms shared by the two disorders. These seizures usually begin with visual hallucinations and can often be triggered by visual stimuli, such as playing video games or staring at a television. This is because images on computer and television monitors are flickering but the brain perceives them as a constant image. Occipital lobe epilepsy accounts for about 5—10 percent of all epilepsy cases (Adcock & Panayiotopoulos, 2012). This is typically due to an unknown cause or due to a lesion in the occipital lobe. Occipital epilepsy usually begins in childhood but may occur at any age.
Renee Johnson and Jennifer L. Hellier
See also: Blindness; Brain Anatomy; Brodmann Areas; Color Perception; Ocular Dominance Columns; Optic Nerve; Visual Perception; Visual System
Adcock, Jane E., & Chrysostomos P. Panayiotopoulos. (2012). Occipital lobe seizures and epilepsies. Journal of Clinical Neurophysiology, 29(5), 397—407.
Hines, Tonya. (2011). Anatomy of the brain. Mayfield Clinic for Brain & Spine. Retrieved from http://www.mayfieldclinic.com/PE-AnatBrain.htm#.U_SJy0tFFfM
Kandel, Eric R., et al. (Eds.). (2012). Principles of neural science (5th ed.). New York, NY: McGraw-Hill.