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Vivien Casagrande; Evolution of visual pathways. Journal of Vision 2005;5(12):32. doi: 10.1167/5.12.32.
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© ARVO (1962-2015); The Authors (2016-present)
Vision is the dominant sense in primates. In this talk I will attempt to reconstruct a reasonable scenario for how parallel visual pathways might have evolved in primates by comparing key factors that might distinguish this group evolutionarily. The focus will be on visual information channels from the eye through the lateral geniculate nucleus (LGN) of the thalamus to cortex since these pathways may have uniquely specialized in primate evolution. I will defend the position that magnocellular (M) and parvocellular (P) retino -geniculo-cortical pathways are homologous across primates and therefore probably existed in the mammalian common ancestor of primates. Whether homologues to these visual pathways can be found in extant mammals remains controversial but evidence suggests that functionally similar pathways can be identified in a range of mammals. Even for the less well-researched koniocellular (K) LGN pathway data exist suggesting an early evolutionary history. Only among primates, however, is the evidence strong enough to support homology. I will also present data suggesting that the common ancestor to primates was dichromatic and that early primates may even have been diurnal given the existence of genes for at least two cone types in all primates. Finally, I will review evidence for the evolutionary history of cortical hierarchies of visual areas and show why only a few areas can be considered homologous across primates and even fewer across mammals.
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