The occipital lobe is one of the four major lobes of the cerebral cortex in the brain of mammals. The name derives from its position at the back of the head, from the Latin , 'behind', and , 'head'.
The occipital lobe is the visual processing center of the mammalian brain, containing most of the anatomical region of the visual cortex. The primary visual cortex is Brodmann area 17, commonly called V1 (visual one). Human V1 is located on the medial side of the occipital lobe within the calcarine sulcus; the full extent of V1 often continues onto the occipital pole. V1 is often also called striate cortex because it can be identified by a large stripe of myelin, the stria of Gennari. Visually driven regions outside V1 are called extrastriate cortex. There are many extrastriate regions, and these are specialized for different visual tasks, such as visuospatial processing, color differentiation, and motion perception. Bilateral lesions of the occipital lobe can lead to cortical blindness (see Anton's syndrome).
Function
The occipital lobe is divided into several functional visual areas. Each visual area contains a full map of the visual world. Although there are no anatomical markers distinguishing these areas (except for the prominent striations in the striate cortex), physiologists have used electrode recordings to divide the cortex into different functional regions.
The dorsomedial (DM) is not as thoroughly studied. However, there is some evidence that suggests that this stream interacts with other visual areas. A case study on monkeys revealed that information from V1 and V2 areas make up half the inputs in the DM. The remaining inputs are from multiple sources that have to do with any sort of visual processing
Retinal sensors convey stimuli through the optic tracts to the lateral geniculate bodies, where optic radiations continue to the visual cortex. Each visual cortex receives raw sensory information from the outside half of the retina on the same side of the head and from the inside half of the retina on the other side of the head. The cuneus (Brodmann's area 17) receives visual information from the contralateral superior retina representing the inferior visual field. The lingula receives information from the contralateral inferior retina representing the superior visual field. The retinal inputs pass through a "way station" in the lateral geniculate nucleus of the thalamus before projecting to the cortex. Cells on the posterior aspect of the occipital lobes' gray matter are arranged as a spatial map of the retinal field. Functional neuroimaging reveals similar patterns of response in cortical tissue of the lobes when the retinal fields are exposed to a strong pattern.
Clinical significance
If one occipital lobe is damaged, the result can be homonymous hemianopsia vision loss from similarly positioned "field cuts" in each eye.
Epilepsy
Recent studies have shown that specific neurological findings have affected idiopathic occipital lobe epilepsies. Occipital lobe seizures are triggered by a flash, or a visual image that contains multiple colors. These are called flicker stimulation (usually through TV); these seizures are referred to as photo-sensitivity seizures. Patients having experienced occipital seizures described their seizures as featuring bright colors, and severely blurring their vision (vomiting was also apparent in some patients). Occipital seizures are triggered mainly during the day, through television, video games or any flicker stimulatory system. Occipital seizures originate from an epileptic focus confined within the occipital lobes. They may be spontaneous or triggered by external visual stimuli. Occipital lobe epilepsies are etiologically idiopathic, symptomatic, or cryptogenic.
Additional images
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File:Gray724.png|Base of brain.
File:Gray1197.png|Drawing to illustrate the relations of the brain to the skull.
File:Brain animated color nevit.gif|Occipital lobe in blue
File:Slide3aa.JPG|Occipital lobe
File:Slide3bb.JPG|Occipital lobe
File:Slide2GRE.JPG|Ventricles of brain and basal ganglia. Superior view. Horizontal section. Deep dissection
</gallery>
See also
- Alpha wave
- Lobes of the brain
- List of regions in the human brain
- Lunate sulcus
- Visual evoked potential
- Vertical occipital fasciculus
- Visual snow syndrome