The occipital lobe is one of the four major lobes of the cerebral cortex in the brain
of mammals.
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.
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 posterior pole of the occipital lobe.
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 discrimination, and motion perception.
The name derives from the overlying occipital bone, which is named from the Latin ob, behind,
and caput, the head.
Bilateral lesions of the occipital lobe can lead to cortical blindness.
Structure
The two occipital lobes are the smallest of four paired lobes in the human cerebral cortex.
Located in the rearmost portion of the skull, the occipital lobes are part of the forebrain.
The cortical lobes are not defined by any internal structural features, but rather by
the bones of the head bone that overlie them.
Thus, the occipital lobe is defined as the part of the cerebral cortex that lies underneath
the occipital bone.
The lobes rest on the tentorium cerebelli, a process of dura mater that separates the
cerebrum from the cerebellum.
They are structurally isolated in their respective cerebral hemispheres by the separation of
the cerebral fissure.
At the front edge of the occipital are several lateral occipital gyri, which are separated
by lateral occipital sulcus.
The occipital aspects along the inside face of each hemisphere are divided by the calcarine
sulcus.
Above the medial, Y-shaped sulcus lies the cuneus, and the area below the sulcus is the
lingual gyrus.
Damage to the primary visual areas of the occipital lobe can leave a person with partial
or complete blindness.
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, physiologists have used electrode
recordings to divide the cortex into different functional regions.
The first functional area is the primary visual cortex.
It contains a low-level description of the local orientation, spatial-frequency and color
properties within small receptive fields.
Primary visual cortex projects to the occipital areas of the ventral stream, and the occipital
areas of the dorsal stream—visual area V3, visual area MT, and the dorsomedial area.
A significant functional aspect of the occipital lobe is that it contains the primary visual
cortex.
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 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.
Occipital lesions can cause visual hallucinations.
Lesions in the parietal-temporal-occipital association area are associated with color
agnosia, movement agnosia, and agraphia.
Damage to the primary visual cortex, which is located on the surface of the posterior
occipital lobe, can cause blindness due to the holes in the visual map on the surface
of the visual cortex that resulted from the lesions.
Epilepsy Recent studies have shown that specific neurological
findings have had an impact on 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 these seizures are referred to as photo-sensitivity
seizures.
Patients having experienced occipital seizures described their seizure as seeing bright colors,
and having severe blurred vision.
Occipital seizure 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.
Symptomatic occipital seizures can start at any age, as well as any stage after or during
the course of the underlying causative disorder.
Idiopathic occipital epilepsy usually starts in childhood.
Occipital epilepsies account for approximately 5% to 10% of all epilepsies.
Additional images
See also This article uses anatomical terminology;
for an overview, see anatomical terminology.
Lobes of the brain Regions of the human brain
Sulcus Lunatus Visual evoked potential
References