The occipital lobe is the rearmost part of the cerebrum that contains the primary and secondary visual cortex. This visual center is primarily responsible for processing and interpreting visual sensory input. As a result of a cerebral infarction, cortical blindness can occur due to damage to this brain region.
What is the occipital lobe?
In neurology, the occipital lobe, or occipital lobe, refers to the rearmost part of the cerebrum. This area is the smallest lobe of the total of 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 localized below it. The occipital lobe attaches to the occipital bone and sits above the cerebellar peduncle, which separates this area of the brain from the cerebellum directly below. The occipital lobe is adjacent to both the temporal and parietal lobes. This area of the brain is also known as the visual center because this is where all visual information is processed. Both the primary and secondary visual cortex are located in this area and are often summarized as visual cortex. Together with the parietal, frontal, and temporal lobes, the occipital lobe makes up the entirety of the cerebrum. To the temporal lobe, the occipital lobe has no clearly identifiable boundary.
Anatomy and structure
The primary visual cortex is also known as the six-layered Brodman area 17 and is located on either side of the sulcus calcarinus. In the inner granular layer of this area lies a band of nerve fibers, also known as the Vicq-d’Azyr strip, which gives the area its striated appearance. The secondary visual cortex is connected by pathways to cerebral cortical areas such as the angular gyrus or frontal lobe. The occipital lobe is connected to the blood supply by veins and arteries. The supply is mainly through the posterior cerebral artery. Blood drains from this area through the ascending superficial cerebral veins and the descending superficial cerebral veins. Both veins are superficial cerebral veins. Blood reaches the superior sagittal sinus via the ascending vein. Blood from the descending vein, on the other hand, enters the transverse sinus, which joins the superior saggital sinus. From the transverse sinus, blood is drained from the brain into the jugular vein and leaves the head in this manner.
Function and tasks
The functions and tasks of the occipital lobe are primarily visual and associative. The primary visual cortex of this area of the brain is where the processing of all visual stimuli from the temporal ipsilateral and nasal contralateral retina takes place. The right occipital lobe processes the signals from the respective right retinal hemispheres and the left part of the structure is responsible for processing the signals from the left retinal hemispheres. Each retinal point is interconnected with a specific area of the primary visual cortex. 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 assemblies in this area also filter out specific information or visual patterns from an overall visual impression. This process is also called feature extraction. Unlike the primary visual cortex, the secondary visual cortex is an association center. This is where interpretation takes place instead of processing. This area corresponds to Brodmann areas 18 and 19, where the final processed visual patterns of the primary visual cortex are juxtaposed with formerly collected sensory impressions. Through this juxtaposition, interpretations of a visual impression become possible. Thus, the recognition of visually perceived events takes place in this area of the brain. Connecting pathways to the angular gyrus and frontal lobe enable the abrupt articulation of a visual impression and the coordination of eye movements.
Diseases
Tissue in the area of the occipital lobe can sustain damage. Most often, such damage presents as a result of trauma or hemorrhage and inflammation. When there is unilateral damage to the primary visual cortex, it usually manifests as contralateral, or opposite, visual field loss.Sometimes only the perception of contrast and brightness is reduced or the affected person perceives a blind spot in a certain part of the visual field. If there is bilateral damage to the primary visual cortex, cortical blindness may occur as a consequence. Eye reflexes are usually preserved. If instead of the primary visual cortex the secondary visual cortex suffers damage, then visual or optic agnosia may develop. Depending on the location and extent of the damage, the affected person no longer recognizes objects, can no longer perceive the overall image of a visual impression, or loses visual perception altogether. Some damage to the secondary visual cortex also manifests itself merely in an inability to recognize writing or to read. In addition to strokes, traumas and inflammations, inflammatory diseases of the central nervous system can also cause tissue of the occipital lobe to perish, for example multiple sclerosis. In some circumstances, disorders of spatial perception or motion perception also occur in the context of an occipital lobe lesion. The most frequent cause of damage to the areas described remains infarctions of the middle and posterior cerebral artery. In contrast, the occipital lobe is only extremely rarely affected by diseases such as Alzheimer’s disease.
