Occipital lobe
Encyclopedia
The occipital lobe is the visual processing center
of the mammal
ian 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 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 oc- + caput, "back of the head".
. The cortical lobes are not defined by any internal structural features, but rather by the bones of the skull that overlie them. Thus, the occipital lobe is defined as the part of the cerebral cortex that lies underneath the occipital bone. (See the human brain
article for more information.)
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
.
Retina
l 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.
If one occipital lobe is damaged, the result can be homonomous
vision loss
from similarly positioned "field cuts" in each eye. Occipital lesion
s can cause visual hallucination
s. Lesions in the parietal-temporal-occipital association area are associated with color agnosia
, movement agnosia
, and agraphia. Damage to the occipital lobe which houses the primary visual cortex can cause blindness because the lesions can produce a hole in the visual map on the surface of the visual cortex.
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 (visual area V2 and visual area V4), and the occipital areas of the dorsal stream—visual area V3, visual area MT (V5), and the dorsomedial area
(DM).
Visual perception
Visual perception is the ability to interpret information and surroundings from the effects of visible light reaching the eye. The resulting perception is also known as eyesight, sight, or vision...
of the mammal
Mammal
Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...
ian brain
Brain
The brain is the center of the nervous system in all vertebrate and most invertebrate animals—only a few primitive invertebrates such as sponges, jellyfish, sea squirts and starfishes do not have one. It is located in the head, usually close to primary sensory apparatus such as vision, hearing,...
containing most of the anatomical region of the visual cortex
Visual cortex
The visual cortex of the brain is the part of the cerebral cortex responsible for processing visual information. It is located in the occipital lobe, in the back of the brain....
. The primary visual cortex is Brodmann area 17
Brodmann area
A Brodmann area is a region of the cerebral cortex defined based on its cytoarchitectonics, or structure and organization of cells.-History:...
, commonly called V1 (visual one). Human V1 is located on the medial
Medial (disambiguation)
Medial has several meanings:* In mathematics, a medial is a set with a binary operation satisfying certain properties, see medial.* In anatomy, a medial is an adjective describing structures near the midline of an animal, see anatomical terms of location or Human Anatomical Terms#Anatomical...
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
Occipital bone
The occipital bone, a saucer-shaped membrane bone situated at the back and lower part of the cranium, is trapezoidal in shape and curved on itself...
, which is named from the Latin oc- + caput, "back of the head".
Anatomy
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 forebrainCerebral hemisphere
A cerebral hemisphere is one of the two regions of the eutherian brain that are delineated by the median plane, . The brain can thus be described as being divided into left and right cerebral hemispheres. Each of these hemispheres has an outer layer of grey matter called the cerebral cortex that is...
. The cortical lobes are not defined by any internal structural features, but rather by the bones of the skull that overlie them. Thus, the occipital lobe is defined as the part of the cerebral cortex that lies underneath the occipital bone. (See the human brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
article for more information.)
The lobes rest on the tentorium cerebelli
Tentorium cerebelli
The tentorium cerebelli or cerebellar tentorium is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes.-Anatomy:...
, a process of dura mater that separates the cerebrum from the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...
. 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
Cuneus
The cuneus is a portion of the human brain in the occipital lobe.The cuneus receives visual information from the contralateral superior retina representing the inferior visual field. It is most known for its involvement in basic visual processing. Pyramidal cells in the cuneus project to...
, and the area below the sulcus is the lingual gyrus
Lingual gyrus
The lingual gyrus of the occipital lobe lies between the calcarine sulcus and the posterior part of the collateral sulcus; behind, it reaches the occipital pole; in front, it is continued on to the tentorial surface of the temporal lobe, and joins the parahippocampal gyrus...
.
Function
Significant functional aspects of the occipital lobe is that it contains the primary visual cortex and is the part of the brain where dreams come from.Retina
Retina
The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...
l 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
Lateral geniculate nucleus
The lateral geniculate nucleus is the primary relay center for visual information received from the retina of the eye. The LGN is found inside the thalamus of the brain....
of the thalamus
Thalamus
The thalamus is a midline paired symmetrical structure within the brains of vertebrates, including humans. It is situated between the cerebral cortex and midbrain, both in terms of location and neurological connections...
before projecting to the cortex. Cells on the posterior aspect of the occipital lobes' gray matter
Gray Matter
"Gray Matter" is a short story by Stephen King, first published in the October 1973 issue of Cavalier magazine, and later collected in King's 1978 collection Night Shift. It is set in the same area as King's novel Dreamcatcher.-Setting:...
are arranged as a spatial map of the retinal field. Functional neuroimaging
Functional neuroimaging
Functional neuroimaging is the use of neuroimaging technology to measure an aspect of brain function, often with a view to understanding the relationship between activity in certain brain areas and specific mental functions...
reveals similar patterns of response in cortical tissue of the lobes when the retinal fields are exposed to a strong pattern.
If one occipital lobe is damaged, the result can be homonomous
Homonymous hemianopsia
Hemianopsia or hemianopia is visual field loss that respects the vertical midline, and usually affects both eyes, but can involve one eye only. Homonymous hemianopsia, or homonymous hemianopia occurs when there is hemianopic visual field loss on the same side of both eyes...
vision loss
Vision loss
Vision loss or visual loss is the absence of vision where it existed before, which can happen either acutely or chronically .-Ranges of vision loss:...
from similarly positioned "field cuts" in each eye. Occipital lesion
Lesion
A lesion is any abnormality in the tissue of an organism , usually caused by disease or trauma. Lesion is derived from the Latin word laesio which means injury.- Types :...
s can cause visual hallucination
Hallucination
A hallucination, in the broadest sense of the word, is a perception in the absence of a stimulus. In a stricter sense, hallucinations are defined as perceptions in a conscious and awake state in the absence of external stimuli which have qualities of real perception, in that they are vivid,...
s. Lesions in the parietal-temporal-occipital association area are associated with color agnosia
Color agnosia
Color agnosia , is a medical or psychological condition that prevents a person from correctly associating hue names with common objects. The sufferer retains the ability of distinguishing hues...
, movement agnosia
Akinetopsia
Akinetopsia, also known as cerebral akinetopsia or motion blindness, is an extremely rare neuropsychological disorder in which a patient cannot perceive motion in their visual field, despite being able to see stationary objects without issue. For patients with akinetopsia, the world becomes devoid...
, and agraphia. Damage to the occipital lobe which houses the primary visual cortex can cause blindness because the lesions can produce a hole in the visual map on the surface of the visual cortex.
Functional anatomy
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 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 (visual area V2 and visual area V4), and the occipital areas of the dorsal stream—visual area V3, visual area MT (V5), and the dorsomedial area
Dorsomedial area
The Dorsomedial area, also known as DM or V6, is a subdivision of the visual cortex of primates first described by John Allman and Jon Kaas in 1975...
(DM).
Epilepsy and the Occipital lobe
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 who have experienced occipital seizures described their seizure as seeing bright colors, and having severe blurred vision(vomiting was also apparent in some patients). Occipital seizure are triggered mainly during the day, through television, video games or any flicker stimulatory system.See also
- Lobes of the brainLobes of the brainBrain lobes were originally a purely anatomical classification, but have been shown also to be related to different brain functions. The telencephalon , the largest portion of the human brain, is divided into lobes, but so is the cerebellum...
- Regions of the human brain
- Sulcus LunatusSulcus LunatusThe Sulcus Lunatus is an inconsistent and small semilunar groove on the occipital lobe of the cerebral cortex. It is considered homologous with the major sulcus of the same name that is more constant in monkeys and apes....
- Visual evoked potential