thumb|Schematic diagram of the primate LGN. Koniocellular neurons not labeled, but are present between the layers.

In neuroscience, koniocellular cells, also called K-cells, are relatively small neurons located in the koniocellular layer of the lateral geniculate nucleus (LGN) within the thalamus of primates, including humans. The term 'koniocellular' is derived .

Koniocellular layers are located ventral to each parvocellular and magnocellular layer of the LGN. Even if the quantity of neurons is approximately equal to the number of magnocellular cells, the koniocellular layers are much thinner due to their size. In comparison to the parvocellular and magnocellular system, fewer studies have been conducted to investigate the koniocellular system. Koniocellular cells are a heterogeneous population differing in many aspects, such as response properties and connectivity.

Structure

K cells are neurochemically and anatomically distinct from M and P cells. There are three proteins by which K cells can be clearly distinguished:

  • Calbindin (28kDa calcium binding protein, CALB)
  • The alpha subunit of type II calmodulin-dependent protein kinase (CAMKIIα)
  • The gamma subunit of protein kinase C (PKC-γ).

Layers

thumbnail|M P and K cells

Ventral to each of the magnocellular and parvocellular layers lie the koniocellular layers, which differ in thickness. In macaques there are two magnocellular and four parvocellular layers, and accordingly six konicellular layers. K1, the layer ventral to M1, is the largest. K2, K3 and K4 are thinner but nonetheless substantial bands of neurons. The two most dorsal layers K5 and K6 are mostly monolayers.

Corticogeniculate axons appear to be quantitatively dominant within the LGN. The same holds for K cells but unlike M and P cells they also receive input from the extrastriate cortex. Axons arising from the superficial grey layer of the superior colliculus terminate in every K layer, with the most ventral layers receiving the strongest input. Thus, it is assumed that the K layers are functionally related to the superior colliculus, e.g. reflexive control of eye movements.

Development and plasticity

It is assumed that K cells generate and migrate contemporaneously with neighboring M and P cells.

Research has shown that there exists a direct pathway from the LGN to MT consisting mostly of koniocellular cells. In fact, 63% of the neurons directly projecting to MT are koniocellular cells. The input MT receives directly from the LGN makes up about 10% of the V1 neuron population projecting to MT. These results suggest that the koniocellular layers play a key role in V1-independent vision. Since the koniocellular layers receive input from the superior colliculus, the previously obtained results can be complemented by the role of the koniocellular layers.

This direct connection from the LGN, more precisely the koniocellular layers, to MT could account for the phenomenon of blindsight as well as for rapid detection of moving objects in healthy subjects.

See also

  • Magnocellular cell
  • Parvocellular cell
  • List of human cell types derived from the germ layers
  • Blindsight
  • Two-streams hypothesis

References