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. It is the largest site of Neuron, neural integration in the central nervous system, and plays ...

in the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s. 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

ian

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 thalam ...

. The

primary 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 ...

Brodmann area 17 The visual cortex of the brain is the area of the cerebral cortex that processes visual perception, visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus ...

, commonly called V1 (visual one). Human V1 is located on the

medial Medial may refer to: Mathematics * Medial magma, a mathematical identity in algebra Geometry * Medial axis, in geometry the set of all points having more than one closest point on an object's boundary * Medial graph, another graph that repr ...

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 Sheath ( ) is a lipid-rich material that in most vertebrates surrounds the axons of neurons to insulate them and increase the rate at which electrical impulses (called action potentials) pass along the axon. The myelinated axon can be lik ...

, 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 e ...

. 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 difficul ...

. Bilateral lesions of the occipital lobe can lead to cortical blindness (see Anton's syndrome).

Structure

The two occipital lobes are the smallest of four paired lobes in the

human brain The human brain is the central organ (anatomy), organ of the nervous system, and with the spinal cord, comprises the central nervous system. It consists of the cerebrum, the brainstem and the cerebellum. The brain controls most of the activi ...

. Located in the rearmost portion of the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, the occipital lobes are part of the posterior

cerebrum The cerebrum (: cerebra), 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 olfac ...

. The lobes of the brain are named from the overlying bone and the

occipital bone The occipital bone () is a neurocranium, cranial dermal bone and the main bone of the occiput (back and lower part of the skull). It is trapezoidal in shape and curved on itself like a shallow dish. The occipital bone lies over the occipital lob ...

overlies the occipital lobes. The lobes rest on the

tentorium cerebelli The cerebellar tentorium or tentorium cerebelli (Latin for "tent of the cerebellum") is one of four dural folds that separate the cranial cavity into four (incomplete) compartments. The cerebellar tentorium separates the cerebellum from the cere ...

, a process of dura mater that separates the cerebrum from the

cerebellum The cerebellum (: cerebella or cerebellums; 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 it or eve ...

. They are structurally isolated in their respective cerebral hemispheres by the separation of the

cerebral fissure The longitudinal fissure (or cerebral fissure, great longitudinal fissure, median longitudinal fissure, interhemispheric fissure) is the deep groove that separates the two cerebral hemispheres of the vertebrate brain. Lying within it is a continu ...

. At the front edge of the occipital lobe are several

occipital gyri The occipital gyri (OcG) are three gyri in parallel, along the lateral portion of the occipital lobe, also referred to as a composite structure in the brain. The gyri are the superior occipital gyrus, the middle occipital gyrus, and the inferior o ...

, 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 (; : cunei) is a smaller lobe in the occipital lobe of the brain. The cuneus is bounded anteriorly by the parieto-occipital sulcus and Inferior (anatomy), inferiorly by the calcarine sulcus. Function The cuneus (Brodmann area 17) r ...

, 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 or ...

. 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), physiologists have used electrode recordings to divide the cortex into different functional regions. The first functional area is the

. It contains a low-level description of the local orientation, spatial-frequency and color properties within small receptive fields.

Primary 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 ...

projects to the occipital areas of the

ventral stream The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct vis ...

( visual area V2 and visual area V4), and the occipital areas of the

dorsal stream The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct vis ...

— visual area V3, visual area MT (V5), and the

dorsomedial area 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 an ...

(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 (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

sensors A sensor is often defined as a device that receives and responds to a signal or stimulus. The stimulus is the quantity, property, or condition that is sensed and converted into electrical signal. In the broadest definition, a sensor is a devi ...

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 In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, Anatomical ter ...

of the

thalamus The thalamus (: thalami; from Greek language, Greek Wikt:θάλαμος, θάλαμος, "chamber") is a large mass of gray matter on the lateral wall of the third ventricle forming the wikt:dorsal, dorsal part of the diencephalon (a division of ...

before projecting to the cortex. Cells on the posterior aspect of the occipital lobes'

gray matter Grey matter, or gray matter in American English, is a major component of the central nervous system, consisting of neuronal cell bodies, neuropil (dendrites and unmyelinated axons), glial cells (astrocytes and oligodendrocytes), synapses, and ...

are arranged as a spatial map of the retinal field.

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. It is primarily used a ...

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 Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes. Homonymous hemianopsia (or homonymous hemianopia) is hemianopic visual field loss on the s ...

vision loss Visual or vision impairment (VI or VIP) is the partial or total inability of visual perception. In the absence of treatment such as corrective eyewear, assistive devices, and medical treatment, visual impairment may cause the individual difficul ...

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 injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

s can cause visual

hallucination A hallucination is a perception in the absence of an external stimulus that has the compelling sense of reality. They are distinguishable from several related phenomena, such as dreaming ( REM sleep), which does not involve wakefulness; pse ...

s. Lesions in the parietal-temporal-occipital association area are associated with

color agnosia Cerebral achromatopsia is a type of color blindness caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina. It is often confused with congenital achromatopsia but the underlying physiologica ...

, 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 neuro ...

. 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- ...

(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 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

References