Structure and Function of the Lateral Geniculate Nucleus
- The lateral geniculate nucleus (LGN) is a structure in the thalamus and a key component of the mammalian visual pathway.
- It is a small, ovoid, ventral projection of the thalamus where the thalamus connects with the optic nerve.
- There are two LGNs, one on the left and another on the right side of the thalamus.
- In humans, both LGNs have six layers of neurons (grey matter) alternating with optic fibers (white matter).
- The LGN has layers of magnocellular cells, parvocellular cells, and koniocellular cells.
- The magnocellular, parvocellular, and koniocellular layers of the LGN correspond with the similarly named types of retinal ganglion cells.
- Koniocellular cells provide a third channel to the visual cortex and may be involved in color perception.
- The parvo- and magnocellular fibers were previously thought to dominate the ventral and dorsal streams, respectively.
- The koniocellular system has been linked with the integration of somatosensory system-proprioceptive information with visual perception.
- The tectopulvinar pathway is another major retino-cortical visual pathway.
- The LGN receives input from the retina, visual cortex, superior colliculus, pretectum, and other brain structures.
- Only a small percentage of LGN input comes from the retina.
- Non-retinal inputs can be excitatory, inhibitory, or modulatory.
- The LGN also receives some inputs from the optic tectum.
- Regions in the brainstem not involved in visual perception also project to the LGN.
- Information leaving the LGN travels out on the optic radiations.
- Axons from the LGN go to the V1 visual cortex.
- Magnocellular and parvocellular layers send their axons to layer 4 in V1.
- Koniocellular layers send their axons primarily to layers 2 and 3 in V1.
- Axons from layer 6 of visual cortex send information back to the LGN.
- The output of the LGN serves several functions in visual perception.
- Computations are achieved to determine the position of every major element in object space relative to the principal plane.
- The LGN accomplishes temporal decorrelation, making for more efficient coding.
- The LGN likely helps the visual system focus its attention on the most important information.
- Neurons from the LGN may travel to higher cortical areas V2 and V3, contributing to blindsight phenomena.

Ipsilateral and Contralateral Layers
- Each LGN receives input from both eyes but only from one half of the visual field.
- RGCs from the nasal sides of each retina cross to the other side of the brain through the optic chiasma.
- RGCs from the temporal sides of each retina remain on the same side of the brain.
- The right LGN receives visual information from the left visual field, and the left LGN receives visual information from the right visual field.
- The sequence of layers receiving information from the ipsilateral and contralateral eyes is different in the tarsier.

Auditory System Interaction
- The LGN likely communicates with the visual system through the peri-reticular nucleus.
- The auditory system influences visual attention through the LGN.
- Lindeberg determined functional models of LGN cells using Laplacian of Gaussian kernels.
- The theory predicts receptive fields that align with biological measurements.
- Non-lagged LGN cells correspond to first-order temporal derivatives, while lagged LGN cells correspond to second-order temporal derivatives.

Color Processing
- The LGN plays a crucial role in early color processing.
- Opponent channels are created in the LGN to compare signals between different photoreceptor cell types.
- P-cells produce red-green opponent signals.
- M-cells contribute to luminance perception without much color opponency.
- K-cells generate blue-yellow opponent signals.

Rodents
- The lateral geniculate nucleus in rodents consists of the dorsal lateral geniculate nucleus (dLGN), ventral lateral geniculate nucleus (vLGN), and the intergeniculate leaflet (IGL).
- These subcortical nuclei have distinct functions.
- The dLGN receives the majority of input from the retina and exhibits retinotopic organization.
- The vLGN is relatively large in various species and has multiple subdivisions.
- The IGL is a small area dorsal to the vLGN and shares similarities with it in terms of neurochemicals and connections.
- The dorsolateral geniculate nucleus is the primary division of the lateral geniculate body.
- It receives most of its input from the retina.
- The dLGN is laminated and exhibits retinotopic organization.
- It plays a crucial role in visual processing.
- The dLGN has distinct functional properties compared to other divisions of the LGN.
- The ventrolateral geniculate nucleus is relatively large in several species.
- It is divided into external and internal divisions.
- The cytoarchitecture of the vLGN differs between species.
- In cats, the vLGN is divided into three regions: medial, intermediate, and lateral.
- The vLGN has reciprocal connections with other thalamic nuclei and receives input from various sources.