EVIDENCE THAT BLUE-ON CELLS ARE PART OF THE 3RD GENICULOCORTICAL PATHWAY IN PRIMATES

Colour vision in primates is mediated by cone opponent ganglion cells in the retina, whose axons project to the dorsal lateral geniculate nu cleus in the visual thalamus. It has long been assumed that cone oppon ent ganglion cells project to the parvocellular layers of the genicula te. Here, we examine the role of a third subdivision of the geniculoco rtical pathway: the interlaminar or koniocellular geniculate relay cel ls. We made extracellular recordings in the dorsal lateral geniculate nucleus of the common marmoset Callithrix jacchus, a New World monkey in which the interlaminar cells are well segregated from the parvocell ular layers. We found that one group of colour opponent cells, the blu e-on cells, was largely segregated to the interlaminar zone. This segr egation was common to dichromatic ('red-green colour-blind') and trich romatic marmosets. The result calls into question the traditional noti on that all colour information passes through the parvocellular divisi on of the retino-geniculo-cortical pathway in primates.