What is the occipital lobe?
Under the occipital lobe or occipital lobe neurology understands the rearmost part of the cerebrum. This area is the smallest lobe of the four brain lobes. The occipital lobe consists of three areas. Together with the sulcus calcarinus, the primary and secondary visual cortex form the entirety of this brain region. Above the sulcus calcarinus lies the cuneus, with the lingual gyrus located below.
The occipital lobe abuts the occipital bone and sits above the cerebellar tent, which separates this brain area from the cerebellum directly below it. The occipital lobe adjoins both the temporal and parietal lobes. The brain area is also known as the visual center because it processes all visual information. Both the primary and secondary visual cortex are located in this area and are often grouped together as a visual cortex. Together with the parietal, the frontal and the temporal lobes, the occipital lobe provides the entirety of the cerebrum. The occipital lobe does not have a clear boundary to the temporal lobe.
Anatomy & Construction
The primary visual cortex is also known as a six-layered Brodman area 17 and lies on both sides of the sulcus calcarinus. In the inner grain layer of this area lies a nerve fiber band, also called Vicq d'Azyr stripe, which gives the area its striped appearance. The secondary visual cortex is connected via pathways with cerebral cortical areas such as the angular gyrus or the frontal lobe. The occipital lobe is attached to the blood supply through veins and arteries.
The supply takes place mainly via the posterior cerebral artery. The ascending venae superficiales ascendentes cerebri and the descending venae superficiales descendentes cerebri drain the blood from this area. Both veins are superficial cerebral veins. The blood reaches the superior sagittal sinus via the ascending vein. In contrast, the blood of the descending vein enters the sinus transversus, which merges with the superior sagittal sinus. From the sinus transversus, the blood is drained from the brain into the jugular vein, leaving the head in this way.
Function & Tasks
The functions and tasks of the occipital lobe are primarily visual and associative. In the primary visual cortex of this brain area, all visual stimuli are processed from the temporal ipsilateral and nasal contralateral retina. The right occipital lobe processes the signals of the respective right retinal halves and the left part of the structure is responsible for processing the signals from the left retina halves.
Each retinal point is linked to a specific area of the primary visual cortex. The incoming information is processed by the primary visual cortex of the occipital lobe in cortical columns. These columns correspond to superimposed associations of cells. Some cell associations in this area also filter out certain information or visual patterns from a visual overall impression. This process is also called property extraction. Unlike the primary visual cortex, the secondary visual cortex is an association center. Here instead of processing interpretation takes place.
This area corresponds to the Brodmann areas 18 and 19. Here, the finished Sehmusters the primary visual cortex are compared with previously collected sensory impressions. This juxtaposition makes it possible to interpret a visual impression. The recognition of the visually perceived thus takes place in this area of the brain. The connecting lanes to the angular gyrus and the frontal lobe allow the abrupt articulation of a visual impression and the coordination of eye movements.
In the area of the occipital lobe the tissue may be damaged. Most commonly, such damage occurs as a result of trauma or bleeding and inflammation. If one-sided damage of the primary visual cortex is present, then this manifests itself usually in the form of contralateral, ie opposite visual field defects. Sometimes only the perception of contrasts and brightnesses is reduced, or those affected perceive a blind spot in a certain part of the visual field.
If there is damage to the primary visual cortex on both sides, then bark blindness may occur as a consequence. The eye reflexes are usually preserved. If, instead of the primary visual cortex, the secondary visual cortex suffers damage, then a visual or visual agnosia may occur. Depending on the location and extent of the injury, the affected persons no longer recognize objects, can no longer perceive the overall picture of a visual impression or lose the visual perception altogether.
Some damage to the secondary visual cortex is also manifested only in an inability to recognize letters or to read and write. In addition to strokes, trauma and inflammation, inflammatory diseases of the central nervous system can also cause tissue obstruction of the occipital lobe, such as multiple sclerosis. Under certain circumstances disturbances of the spatial perception or the movement perception occur within the framework of an occipital lobe lesion. The most common cause of damage to the areas described remain infarcts of the middle and posterior cerebral artery. By contrast, diseases such as Alzheimer's rarely affect the occipital lobe.