Lateral geniculate nucleus
The LGN receives information directly from the ascending retinal ganglion cells via the optic tract and from the reticular activating system.Neurons of the LGN send their axons through the optic radiation, a direct pathway to the primary visual cortex.[1] In humans as well as other mammals, the two strongest pathways linking the eye to the brain are those projecting to the dorsal part of the LGN in the thalamus, and to the superior colliculus.The sequence of layers receiving information from the ipsilateral and contralateral (opposite side of the head) eyes is different in the tarsier.Regions in the brainstem that are not involved in visual perception also project to the LGN, such as the mesencephalic reticular formation, dorsal raphe nucleus, periaqueuctal grey matter, and the locus coeruleus.[12] Information leaving the LGN travels out on the optic radiations, which form part of the retrolenticular portion of the internal capsule.Studies involving blindsight have suggested that projections from the LGN travel not only to the primary visual cortex but also to higher cortical areas V2 and V3.Computations are achieved to determine the position of every major element in object space relative to the principal plane.Like other areas of the thalamus, particularly other relay nuclei, the LGN likely helps the visual system focus its attention on the most important information.The LGN is integral in the early steps of color processing, where opponent channels are created that compare signals between the different Photoreceptor cell types.[27] The ventrolateral geniculate nucleus has been found to be relatively large in several species such as lizards, rodents, cows, cats, and primates.The external and internal divisions are separated by a group of fine fibers and a zone of thinly dispersed neurons.[31] The vLGN and IGL appear to be closely related based on similarities in neurochemicals, inputs and outputs, and physiological properties.The vLGN and IGL have been reported to share many neurochemicals that are found concentrated in the cells, including neuropeptide Y, GABA, encephalin, and nitric oxide synthase.Other connections that have been found to be reciprocal include the superior colliculus, pretectum, and hypothalamus, as well as other thalamic nuclei.
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