Visual cortex

The visual cortex ( also visual cortex ) is that part of the cerebral cortex, which is listed as the visual system, which in turn allows for visual perception. The visual cortex occupies the major part of the occipital lobe of the brain. After the brain map of Korbinian Brodmann, coincident with the areas 17, 18 and 19 It is divided into the primary visual cortex (V1 ) and secondary or tertiary (associative, V2 -V5 ) regions. Histologically characterized him in primates to the high cell density and the relatively small thickness ( in humans 1.5-2 mm). The area 17 (also striate area ) represents directly the reciprocal half of the visual field and is " retinotopically " built up, which means that on the retina ( retina) adjacent points are shown here side by side. The cells representing the fovea are, thereby significantly over-represented and occupy about half the area striata.

Primary visual cortex ( V1)

Histology

The primary visual cortex ( Brodmann 's area 17, V1, striate area ) is like the entire neocortex ( distinguished from Archi - and Paleocortex ) divided into six layers:

• Layer I: molecular layer
• Layer II: outer nuclear layer
• Layer III: external pyramidal layer
• Layer IV: inner nuclear layer
• Layer V: inner pyramidal cell layer
• Layer VI: multiforme layer.

In addition to the layers of organization arises in V1, as in the rest of the cortex also a kollumnäre ( columnar ) structure here each represents an orientation.

Afferents and internal organization

The primary visual cortex area V1 has a particularly thick layer IV Here ends of many afferent fibers of the neurons of the lateral geniculate nucleus (CGL ). The layer IV are further subdivided into A, B and C, C in turn Cα and Cβ. In IVCα layer forming the axons of the magnocellular layers 1 and 2 of the CGL. These neurons in turn are derived from ganglion cells of the retina with large receptive fields from which have a high temporal but low spatial resolution. The work of David Hubel and Torsten Wiesel provided the insight that neurons of the layer IVCα are orientation selective. Individual groups of these cells respond to visual stimuli, respectively along the center of their elongated receptive fields up to a deviation of 10 °. These cells are called simple cells. They project into the layer IVB, where they are connected binocular and direction selectivity have (M- channel).

Parvocellular neurons of layers III- VI of the CGL terminate in layer IVCβ and to a lesser extent in layer IVA and I. You will receive afferents of the ganglion cells with small receptive fields ( fovea ) exhibit color sensitivity and have a high spatial resolution.

From the inputs of the layer IVCα more cortexareale get the information about movements in the visual field. From the inputs of the layer IVCβ other cortexareale get the information on the form and partially color of objects in the visual field.

Lesions of the magnocellular layers in monkeys had the consequence that these lost the ability of motion perception, whereas damage to the parvocellular layers prevented the perception of color, fine textures and shapes and spatial depth.

The layer IV ocular dominance has straps that can be represented by retrograde axonal transport of radioactive proline ( or other amino acids ).

Secondary and tertiary visual cortex (V2 -V5 )

The V2 is situates on the areas of Korbinian Brodmann in Area 18 and has a stripe structure, which can be made visible by histological staining of Cytochromoxidaseaktivität. These strips are linked to the processing of individual aspects of perception, shape perception and stereo vision to Livingstone and Hubel (1988) and then have efferent fibers in the higher areas of the brain.

After the interconnection in V1 and V2, the processing is divided into a dorsal pathway through the parietal lobe in the motor areas along the central sulcus and the ventral pathway, which leads into the areas of the temporal lobe, which is ascribed to the beginning of the object recognition. The ventral pathway V4 among others and expect the inferotemporal cortex. The dorsal path runs (also called mediotemporaler cortex) through V5. The Assoziationscortices, however, are overall not as accurately charted such as V1, as it leads to inter-individual differences.