Phylogenetical changes and functional specializations in the dorsal lateral geniculate nucleus (dLGN) of mammals

Depending on their visual specialization and their place in the zoological system the mammalian species show some peculiarities in the morphology of the dorsal lateral geniculate nucleus (dLGN). The lamination of dLGN can be find in mammals with a highly developed visual system and a proportionally big part of ipsilaterally projecting retinogeniculate fibres. Number and sequence of ipsi- and contralaterally innervated laminae varies between species of different taxonomical categories. Hence these features depend on phylogenetical trends which could traced back to the beginning of the "mammalian radiation" in the cretaceous period and the earliest tertiary. Ancestral conditions may be found in mammals with an unlaminated dLGN and a medially located ipsilaterally innervated part. It may be registrated that a cytoarchitectonical separation of laminae (concerning the ipsi- and contralateral innervation) is the secondary step after fibre anatomical separation. The most primitive status may be realized in mammals having a zone of mixed ipsi- and contralateral fibre input. Some conclusions are made with regard to the suitability of lab mammals for generalization of results in the dLGN morphology.