Structure

The left and the right LGN is a distinctively layered structure ("geniculate" means "bent like a knee"). In most primates, including humans, it has six layers of cell bodies with layers of neuropil in between, in an arrangement something like a club sandwich or layer cake, with cell bodies of LGN neurons as the "cake" and neuropil as the "icing".

[edit] M, P, K cells Type Function Location Projection The cells in layers 1 and 2 are large, or magnocellular (M) Magnocellular cells have large cell bodies, use a relatively short time to process information. This system operates quickly but without much detail. They are found in layers 1 and 2 of the LGN, those layers more ventrally located which are next to the incoming optic tract fibers. M Cells are the retinal ganglion cells that project their axons to the magnocellular layers of the LGN. Others in layers 3, 4, 5, and 6 are smaller, or parvocellular (P). (The Latin prefix "parvo-" means "small"; some authors prefer the term parvicellular. If you're searching for more information, try both spellings.) Parvocellular cells have small cell bodies, and use a relatively long time to process information. This system operates more slowly and with lots of information about details. For example, these cells carry color information while magnocellular cells do not. Parvocellular cells are found in layers 3, 4, 5 and 6. P Cells are the retinal ganglion cells that project their axons to the parvocellular layers of the LGN. Between each of the M and P layers lies a zone of very small cells: the interlaminar, or koniocellular (K), layers. K cells are functionally and neurochemically distinct from M and P cells and provide a third channel to the visual cortex. Koniocellular cells have very small cell bodies and are located in between the layers. The role of the koniocellular system in visual perception is presently unclear, however, it has been linked with integrating somatosensory-proprioceptive information with visual perception, and may also be involved in color perception. - K Cells are the retinal ganglion cells that project their axons to the koniocellular layers of the LGN.

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