M, P, K Cells
| Type | Size* | Source / Type of Information | Location | Response | Number |
| M: Magnocellular cells | Large | Rods; necessary for the perception of movement, depth, and small differences in brightness | Layers 1 and 2 | rapid and transient | ? |
| P: Parvocellular cells (or "parvicellular") | Small | Cones; long- and medium-wavelength ("red" and "green" cones); necessary for the perception of color and form (fine details). | Layers 3, 4, 5 and 6 | slow and sustained | ? |
| K: Koniocellular cells (or "interlaminar") | Very small cell bodies | Short-wavelength "blue" cones. | Between each of the M and P layers |
- Size relates to cell body, dendritic tree and receptive field
The magnocellular, parvocellular, and koniocellular layers of the LGN correspond with the similarly named types of ganglion cells.
Koniocellular cells are functionally and neurochemically distinct from M and P cells and provide a third channel to the visual cortex. They project their axons between the layers of the lateral geniculate nucleus where M and P cells project. Their role in visual perception is presently unclear; however, the koniocellular system has been linked with the integration of somatosensory system-proprioceptive information with visual perception, and it may also be involved in color perception.
The parvo- and magnocellular fibers were previously thought to dominate the Ungerleider-Mishkin ventral stream and dorsal stream, respectively. However, new evidence has accumulated showing that the two streams appear to feed on a more even mixture of different types of nerve fibers.
The other major retino-cortical visual pathway is the tectopulvinar pathway, routing primarily through the superior colliculus and thalamic pulvinar nucleus onto posterior parietal cortex and visual area MT.
Read more about this topic: Lateral Geniculate Nucleus
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