Occipital lobe

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Occipital cortex
)

Occipital lobe
Lobes of the human brain (the occipital lobe is shown in red)
Medial surface of left cerebral hemisphere. (Cuneus and lingual gyrus are at left.)
Details
Part ofCerebrum
ArteryPosterior cerebral artery
Identifiers
Latinlobus occipitalis
MeSHD009778
NeuroNames140
NeuroLex IDbirnlex_1136
TA98A14.1.09.132
TA25480
FMA67325
Anatomical terms of neuroanatomy

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 ob, 'behind', and caput, 'head'.

The occipital lobe is the

Anton's syndrome
).

Structure

Diagram of gyri of brain viewed on lateral hemisphere. Occipital gyri shown lower right
Animation. Occipital lobe (red) of left cerebral hemisphere.

The two occipital lobes are the smallest of four paired lobes in the human brain. Located in the rearmost portion of the skull, the occipital lobes are part of the posterior cerebrum. The lobes of the brain are named from the overlying bone and the occipital bone overlies the occipital lobes.

The lobes rest on 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, and the area below the sulcus is the lingual gyrus.

Damage to the primary visual areas of the occipital lobe can cause partial or complete blindness.[2]

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.[citation needed
]

The first functional area is 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.[3]

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 [4]

A significant functional aspect of the occipital lobe is that it contains the primary visual cortex.[citation needed]

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

color agnosia, movement agnosia, and agraphia. Lesions near the left occipital lobe can result in pure alexia (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.[5]

Epilepsy

Recent studies have shown that specific neurological findings have affected idiopathic occipital lobe

epilepsies.[6] 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.[7] 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.[8] 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.[8] Occipital epilepsies account for approximately 5% to 10% of all epilepsies.[8]

Additional images

  • Base of brain.
    Base of brain.
  • Drawing to illustrate the relations of the brain to the skull.
    Drawing to illustrate the relations of the brain to the skull.
  • Occipital lobe in blue
    Occipital lobe in blue
  • Occipital lobe
    Occipital lobe
  • Occipital lobe
    Occipital lobe
  • Ventricles of brain and basal ganglia. Superior view. Horizontal section. Deep dissection
    Ventricles of brain and basal ganglia. Superior view. Horizontal section. Deep dissection

See also

References

  1. ^ "SparkNotes: Brain Anatomy: Parietal and Occipital Lobes". Archived from the original on 31 December 2007. Retrieved 27 February 2008.
  2. ^ Schacter, D. L., Gilbert, D. L. & Wegner, D. M. (2009). Psychology. (2nd ed.). New York: Worth Publishers.
  3. ^ Valyear, Culham, Sharif, Westwood, & Goodale, 2006.
  4. ^ Valyear et al., 2006.
  5. .
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  8. ^ .