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The occipital lobe is one of the four major lobes of the
cerebral cortex The cerebral cortex, also known as the cerebral mantle, is the outer layer of neural tissue of the cerebrum of the brain in humans and other mammals. The cerebral cortex mostly consists of the six-layered neocortex, with just 10% consisting o ...
in the
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
of
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
s. The name derives from its position at the back of the head, from the Latin ''ob'', "behind", and ''caput'', "head". The occipital lobe is the visual processing center of the
mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...
ian
brain A brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as Visual perception, vision. I ...
containing most of the anatomical region of the
visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus ...
. 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 Myelin is a lipid-rich material that surrounds nerve cell axons (the nervous system's "wires") to insulate them and increase the rate at which electrical impulses (called action potentials) are passed along the axon. The myelinated axon can ...
, the Stria of Gennari. Visually driven regions outside V1 are called
extrastriate cortex The extrastriate cortex is the region of the occipital cortex of the mammalian brain located next to the primary visual cortex. Primary visual cortex (V1) is also named striate cortex because of its striped appearance in the microscope. The extr ...
. There are many extrastriate regions, and these are specialized for different visual tasks, such as visuospatial processing, color differentiation, and
motion perception Motion perception is the process of inferring the speed and direction of elements in a scene based on visual, vestibular and proprioceptive inputs. Although this process appears straightforward to most observers, it has proven to be a difficult ...
. Bilateral lesions of the occipital lobe can lead to cortical blindness (see
Anton's syndrome Anton syndrome, also known as Anton's blindness and visual anosognosia, is a rare symptom of brain damage occurring in the occipital lobe. Those who have it are cortically blind, but affirm, often quite adamantly and in the face of clear evidenc ...
).


Structure

The two occipital lobes are the smallest of four paired lobes in the
human brain The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of ...
. Located in the rearmost portion of the
skull The skull is a bone protective cavity for the brain. The skull is composed of four types of bone i.e., cranial bones, facial bones, ear ossicles and hyoid bone. However two parts are more prominent: the cranium and the mandible. In humans, th ...
, the occipital lobes are part of the posterior
cerebrum The cerebrum, telencephalon or endbrain is the largest part of the brain containing the cerebral cortex (of the two cerebral hemispheres), as well as several subcortical structures, including the hippocampus, basal ganglia, and olfactory bulb. ...
. The lobes of the brain are named from the overlying bone and the occipital bone overlies the occipital lobes. The lobes rest on the
tentorium cerebelli The cerebellar tentorium or tentorium cerebelli ( Latin for "tent of the cerebellum") is an extension of the dura mater that separates the cerebellum from the inferior portion of the occipital lobes. Structure The cerebellar tentorium is an arc ...
, a process of dura mater that separates the cerebrum from the
cerebellum The cerebellum (Latin for "little brain") is a major feature of the hindbrain of all vertebrates. Although usually smaller than the cerebrum, in some animals such as the mormyrid fishes it may be as large as or even larger. In humans, the cerebe ...
. They are structurally isolated in their respective cerebral hemispheres by the separation of the cerebral fissure. At the front edge of the occipital lobe are several 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 The cuneus (; plural cunei) is a smaller lobe in the occipital lobe of the brain. The cuneus is bounded anteriorly by the parieto-occipital sulcus and inferiorly by the calcarine sulcus. Function The cuneus (Brodmann area 17) receives visu ...
, and the area below the sulcus is the
lingual gyrus The lingual gyrus, also known as the ''medial'' occipitotemporal gyrus, is a brain structure that is linked to processing vision, especially related to letters. It is thought to also play a role in analysis of logical conditions (i.e., logical ord ...
. Damage to the primary visual areas of the occipital lobe can cause 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 (except for the prominent striations in the
striate cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus a ...
), 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 The receptive field, or sensory space, is a delimited medium where some physiological stimuli can evoke a sensory neuronal response in specific organisms. Complexity of the receptive field ranges from the unidimensional chemical structure of od ...
. 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 streamvisual area V3, visual area MT (V5), and the dorsomedial area (DM). The ventral stream is known for processing the "what" in vision, while the dorsal stream handles the "where/how". This is because the ventral stream provides important information for the identification of stimuli that are stored in memory. With this information in memory, the dorsal stream is able to focus on motor actions in response to the outside stimuli. Although numerous studies have shown that the two systems are independent and structured separately from another, there is also evidence that both are essential for successful perception, especially as the stimuli take on more complex forms. For example, a case study using fMRI was done on shape and location. The first procedure consisted of location tasks. The second procedure was in a lit-room where participants were shown stimuli on a screen for 600 ms. They found that the two pathways play a role in shape perception even though location processing continues to lie within the dorsal stream. 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 A significant functional aspect of the occipital lobe is that it contains the primary visual cortex.
Retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...
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 The thalamus (from Greek θάλαμος, "chamber") is a large mass of gray matter located in the dorsal part of the diencephalon (a division of the forebrain). Nerve fibers project out of the thalamus to the cerebral cortex in all direct ...
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 Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment� ...
from similarly positioned "field cuts" in each eye. Occipital
lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by disease or trauma. ''Lesion'' is derived from the Latin "injury". Lesions may occur in plants as well as animals. Types There is no designated classif ...
s can cause visual hallucinations. Lesions in the parietal-temporal-occipital association area are associated with color agnosia, movement agnosia, and
agraphia Agraphia is an acquired neurological disorder causing a loss in the ability to communicate through writing, either due to some form of motor dysfunction or an inability to spell. The loss of writing ability may present with other language or neur ...
. Lesions near the left occipital lobe can result in
pure alexia Pure alexia, also known as agnosic alexia or alexia without agraphia or pure word blindness, is one form of alexia which makes up "the peripheral dyslexia" group. Individuals who have pure alexia have severe reading problems while other language-r ...
(alexia without 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 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. 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 Occipital epilepsy is a neurological disorder that arises from excessive neural activity in the occipital lobe of the brain that may or may not be symptomatic. Occipital lobe epilepsy is fairly rare, and may sometimes be misdiagnosed as migraine ...
usually starts in childhood. Occipital epilepsies account for approximately 5% to 10% of all epilepsies.


Additional images

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


See also

* Alpha wave * Lobes of the brain *
List of regions in the human brain The human brain anatomical regions are ordered following standard neuroanatomy hierarchies. Functional, connective, and developmental regions are listed in parentheses where appropriate. Hindbrain (rhombencephalon) Myelencephalon *M ...
* Lunate sulcus * Visual evoked potential * Vertical occipital fasciculus * Visual snow syndrome


References

{{Authority control Cerebrum